ALBERT R, MANN 
 
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Cornell XDiniversit^ 
 
 Xibrari? 
 
 OF THE 
 
 IRew l^ort? State Colleae of agriculture 
 
 ftc^ill3^ aJMlii 
 
 3778 
 
PKINCIPLES 
 
 OF 
 
 IRRIGATION ENGINEERING 
 
McGraw-Hill DookCoitipairyr 
 
 Pu6d's/iers qf^ooJ^/br 
 
 Electrical World TheEiigjneei-ing andMining Journal 
 En5inGe'ririg Record Engineering News 
 
 Gailw^ Age Gazette American Machinist 
 
 Signal EnginG>er American Engnea- 
 
 ElectricUailway Journal Coal Age 
 
 Metallurgical and Chemical Engineering Powder 
 
PEINCIPLES 
 
 OF 
 
 IREIGATION ENGINEERING 
 
 ARID LANDS, WATER SUPPLY, STORAGE 
 
 WORKS, DAMS, CANALS, WATER 
 
 RIGHTS AND PRODUCTS 
 
 FREDERICK HAYNES NEWELL 
 
 DIRECTOR IT. S. RECLAMATION SERVICE. 
 
 AND 
 
 DANIEL WILLIAM MURPHY 
 
 A. B., A. M., Ph. D. 
 
 ENGIXEEB IN CHARGE OF DRAINAGE U. S. 
 RECLAMATION SERVICE. 
 
 McGRAW-HILL BOOK COMPANY 
 239 WEST 39TH STREET, NEW YORK 
 6 BOUVERIE STREET, LONDON, B. C. 
 
 • 1913 
 
l^lZ<t 
 
 Copyright, 1913, by the 
 McGraw-Hill Book Company 
 
 THB.MAPIiB-PKESS.TOBK.PA 
 
PREFACE 
 
 In the following pages an attempt is made to give an outline of the 
 fundamental questions involved in undertaking and carrying out an 
 irrigation enterprise. In presenting this matter in the form of a 
 treatise on Irrigation Engineering, it is intended primarily for the use 
 of students and engineers who desire to become acquainted with the 
 general principles involved in considering the feasibility of, and 
 in planning, constructing and operating irrigation systems. An 
 attempt has also been made, however, to present the subject mat- 
 ter in such form that it may be read with profit by persons inter- 
 ested in irrigation, but without a thorough technical knowledge of 
 the subject of hydraulics. 
 
 It is not possible in a book of ordinary length, to go into all of the 
 details essential to successful irrigation construction and operation. 
 The broader and more general aspects of the subject therefore are 
 presented with the assumption, that where further details are neces- 
 sary, it will be possible for the student to find them in one of the many 
 technical books now available. The purpose of the work is therefore 
 to assist the student and engineer by pointing out the essential ques- 
 tions to which special attention must be given. 
 
 In attempting to give this broad survey, the presentation has been 
 made as simple and concise as possible. It is appreciated that even 
 with engineers of large experience, there are certain broad principles, 
 which though elementary, are worthy of frequent reconsideration. 
 These principles when applied to new problems are frequently sug- 
 gestive of different viewpoints and lead to a more thorough under- 
 standing of the work in hand. The designation, "The Principles of 
 Irrigation Engineering," has thus been selected as indicative of the 
 attempted scope of the work. 
 
 Irrigation Engineering in its broadest aspects may be defined as 
 the development of the water resources of the arid regions as relating 
 to their conservation and use as a part of the wealth of the nation. 
 More specifically, it deals with the methods of holding, controlling 
 and distributing the waters needed in agriculture, and further, those 
 matters which lead to financial success in the investments then 
 made. As a science or branch of knowledge, it is the result of 
 
VI PREFACE 
 
 investigations worked out and information collected and systema- 
 tized. It should furnish knowledge concerning the water supply 
 and its use, especially as applied to human needs and happiness. 
 It may be studied from the point of view of the statesman con- 
 cerned with questions of public welfare, by the capitalist seeking 
 an investment, and by the engineer, called upon to plan irrigation 
 works. 
 
CONTENTS 
 
 Page 
 Preface . . v 
 
 List of Plates xi 
 
 CHAPTER I 
 
 Irrigation . i 
 
 Definition — History and development — Needs and benefits — Methods 
 of irrigation — Comparison of irrigated and non-irrigated lands. 
 
 CHAPTER II 
 
 Irrigable Lands ... ... 8 
 
 Arid region — Topographic features — The soil — Preparation of lands — 
 Location — Intensive farming — Climate. 
 
 CHAPTER III 
 
 Water Supply 15 
 
 Source of water supply — Character of supply — Benefits of control — 
 Study of water supply — Rainfall — Runoff — Influences affecting runoff 
 — Character of watershed — Evaporation — Runoff on different water- 
 sheds — Comparison of runoff — Measurement of water — Units of 
 measurement — Convenient equivalents — Methods of measurement — 
 Results of stream measurement — Quality of water supply — Amount of 
 water required for irrigation 
 
 CHAPTER IV 
 
 Design and Construction of Canals . -35 
 
 Capacity — Location of canals — Alignment — Cross-section — Slopes and 
 width of banks — Material for banks — Grades and velocities — Excava- 
 tion — Specifications for excavation — Protection against seepage in 
 canals — ^Lined canals — Roadways on banks — Lateral drainage — Right- 
 of-way for canals. 
 
 CHAPTER V 
 
 Canal Structures .61 
 
 Classification — Permanent and temporary structures — Headgates — 
 Operating device — Turnouts — Checks and drops — Wasteways — Cul- 
 verts — Flumes — Velocity and flow of water in flumes — Tunnels — ^Lining 
 — Inverted siphons — Bridges — Measuring devices — Screens— Protec- 
 tion of canal structures. 
 
 vii 
 
viii CONTENTS 
 
 CHAPTER VI 
 
 Page 
 
 Distribution Systems ... . 102 
 
 Canals and laterals — General plan of distribution system — Topo- 
 graphic surveys for lateral systems — Capacity of laterals — ^Location of 
 laterals — Cross-secton of laterals — Points of delivery of water — Delivery 
 box — Flumes and pipe distributaries — Accessibility to laterals. 
 
 CHAPTER VII 
 
 Irrigation by Pumping . . . . . 116 
 
 General conditions — Source of supply — Character of pumps — Power 
 for pumping — Wind-mills — Steam power — Gasoline and oU — Water 
 power — Compressed air — Hydroelectric power — Cost of pumping — 
 Feasibility of pumping. 
 
 CHAPTER Vlll 
 
 Drainage ... 136 
 
 Classification — Needs of drainage — Alkali and its effect — Benefit of 
 drainage — Ground water — Effects of drainage on soils — Open and closed 
 drains — Relief and intercepting drains — Drainage investigations- 
 Capacity of drains — Depth of drains — Distance between drains — 
 Grades and velocities of flow in drains. 
 
 CHAPTER IX 
 
 Operation and Maintenance ... .152 
 
 Distribution of water — Continuous flow — Periodic rotation — ^Length 
 of irrigation season — Frequency of irrigation — Duty of water — Measure- 
 ment of water used — Human element — Maintenance — Priming — Care 
 of banks — Cleaning canals — Organization for operation and mainte- 
 nance — Records — Costs. 
 
 CHAPTER X 
 
 Storage Works . ... 170 
 
 Determination of storage supply — Annual runoff — Amount of runoff 
 that can be stored-^Seepage losses — Evaporation losses — Ratio of 
 runoff to the storage capacity — Determination of storage required — 
 Economic questions in storage — Cost of storage 
 
 CHAPTER XI 
 
 Reservoir Sites 185 
 
 General requirements — Survey of Reservoir sites — Contour maps — 
 Computation of capacities — Choice of reservoir site — Shallow and 
 deep reservoirs. 
 
CONTENTS IX 
 
 CHAPTER XII 
 
 Page 
 Dam Sites .... . . 190 
 
 General conditions — Surveys of dam sites — Foundation — Borings and 
 test pits— Character of foundations — Character of materials for con- 
 struction — Accessibility of materials for construction — Spillway — 
 Records of stream flow — Kind of dam best adapted to suit conditions. 
 
 CHAPTER XIII 
 
 Timber Dams . ■ 2°° 
 
 Kinds of dams — Early stages of development — Use of timber dams — 
 Where timber dams are applicable — Conditions of Stability — Water- 
 tightness — Types of timber dams — ^Log and brush dams — Crib dams — 
 Crib and pile dams — Framed dams — Limits of height. 
 
 CHAPTER XIV 
 
 Earth Dams ..211 
 
 Site for earth dams — Foundation — Selection of materials — Section of 
 dam — Prevention of seepage imder dam — Placing of materials in the 
 dam — Placing of materials by hydraulic method — Compacting the mate- 
 rial — Prevention of seepage through the dam — Core wall — Puddle 
 core — Water-tight face — Cut-off trenches — Protection of slopes — 
 Drainage of dam — Dikes — ^Limits of height of earth dams — Ex- 
 amples of earth dams. 
 
 CHAPTER XV 
 
 Rock-fill Dams 220 
 
 Description — Advantages over earth dams — Site to which adapted — 
 Foundation — Materials — Section and slopes — Water-tight section. 
 
 CHAPTER XVI 
 
 Masonry Dams ■ . 232 
 
 Principles of Construction — Kinds of masonry dams — Rubble concrete 
 — Foundations — Section — Concrete — Upward pressure — Curved dams 
 — Multiple arch dams — Internal stresses — Safe limits for foundations — 
 Overflow dams — Protection of lower toe from erosion — Safe heights — 
 Typical masonry dams. 
 
 CHAPTER XVII 
 
 Otttlet Works . 24S 
 
 Capacity — ^Location — ^Location of gates — Gate towers — Operation of 
 gates — Erosion due to high velocities — Vibration of gates — Character of 
 gates — Fishways — Spilling requirements — Spillway design — Determi- 
 nation of capacity — ^Location and type — Grades and velocities — Pro- 
 tection against erosion. 
 
X CONTENTS 
 
 CHAPTER XVIII 
 
 Page 
 
 Water Rights . 263 
 
 Definition — Origin of water rights in the United States — Riparian 
 
 rights — Acquisition of water rights — Theory upon which granted — 
 
 Beneficial use of water — Water rights apart from lands. 
 
 CHAPTER XIX 
 
 Economic Features op Irrigation . . . . . 275 . 
 
 Feasibility of irrigation — Fundamental questions to be considered — 
 Value of land — Increase in value — Soil, climate and crops — Permanence 
 of water supply — Cost of constructing works — Other costs — Markets 
 and transportation facilities — Security of investment — Ultimate results. 
 
 Index . . 286 
 
LIST OF PLATES 
 
 Facing Page 
 Plate I . . . .... . 4-5 
 
 Fig. A. — Diverting dam in the Boise River, Idaho, a typical structure for 
 taking out river water by gravity. 
 
 Fig. B. — Main northside canal of Minidoka Project, Idaho, illustrative of 
 the larger irrigation canals, with power transmission lines located on the 
 bank. 
 
 Fig. C. — Water being distributed to the fields through furrows after 
 having been diverted from the river by gravity canals. 
 
 Fig. D. — Water being applied to the fields by flooding. 
 Plate II . . . . . 26-27 
 
 Fig. A. — A method of making a measurement of the amount of water in a 
 stream, using current meter from bridge. 
 
 Fig. B. — Making similar measurements by wading. 
 
 Fig. C. — Meters used for measuring the velocity of the flowing water. 
 Plate III . 48-49 
 
 Fig. A. — Constructing canal in earth by means of four-horse Fresno 
 scrapers, Minidoka Project, Idaho. 
 
 Fig. B. — Throwing up small laterals by means of four- horse road ma- 
 chine, Huntley Project, Mont. 
 
 Fig. C. — Excavating canal by use of excavator with belt conveyor, drawn 
 by traction engine. Belle Fourche Project, S. Dak. 
 
 Fig. D. — Finished canal with both upper and lower banks. Lower Yellow- 
 stone Project, Mont. 
 Plate IV . . ... 54-55 
 
 Fig. A. — Enlarging canal by means of floating dipper dredge. Salt River 
 Project, Ariz. 
 
 Fig. B. — Enlarging canal by use of excavator with drag-line working from 
 one side of canal, Salt River Project, Ariz. 
 
 Fig. C. — ^Lining canal with concrete to increase the capacity and reduce 
 the seepage, Boise Project, Idaho. 
 
 Fig. D. — Concrete lined canal in shattered rock, carrying water of 
 Truckee River to Carson River, Truckee-Carson Project, Nevada. 
 Plate V . ... . 62-63 
 
 Fig. A. — Wooden headgates, typical of those usually built for the earlier 
 canals, Jordan and Salt Lake City canal, Utah. 
 
 Fig. B. — Concrete headworks with steel gates, Interstate canal. North 
 Platte Project, Neb. 
 
 Fig. C. — Concrete headworks and roadway, Mesilla Valley canal, Rio 
 Grande Project, New Mexico.' 
 
 Fig. D. — Concrete headworks with sluice gates at Laguna dam on Colo- 
 rado River, Ariz.-Cal. 
 
 xi 
 
xii LIST OF PLATES 
 
 Facing Page 
 
 Plate VI ... . . 80-81 
 
 Fig. A. — Series of checks and drops with inclined chutes terminating in 
 
 water cushion with concrete blocks to break the force of the water, 
 
 North Platte Project, Neb. 
 Fig. B. — Notched check and drop with projecting lip beneath each notch 
 
 to diffuse and break the force of the falling water, Rio Grande Project, 
 
 New Mexico. 
 Fig. C. — Concrete chute, built instead of a series of drops, and terminating' 
 
 in a water cushion with concrete baffle board, Boise Project, Idaho. 
 Fig. D. — Spillway lip to automatically permit escape of excess water' from 
 
 canal back into river and sluice gates provided to facilitate scouring out 
 
 of materials deposited in upper portion of canal. Salt River Project, 
 
 Ariz. 
 Plate VII .. . . 88-89 
 
 Fig. A. — Concrete flume carrying water of main canal across side drainage 
 
 lines, North Platte Project, Wyo.-Neb. 
 Fig. B. — Concrete inverted siphon carrying water of main canal under side 
 
 drainage line instead of over it. North Platte Project, Wyo.-Neb. 
 Fig. C. — Concrete pressure pipe used in place of flume. Sun River Project, 
 
 Mont. 
 Fig. D. — Metal flume on timber trestle. 
 Plate VIII . . . iio-m 
 
 Fig. A. — Distributing laterals with wooden boxes and gates, typical of 
 
 the pioneer work in irrigation, Yakima Project, Wash. 
 Fig. B. — Concrete box and drop on distributory in place of earlier form of 
 
 wooden construction, Orland Project, Cal. 
 Fig. C. — Cast-iron valves on distributing system instead of the usual 
 
 wooden gates, Uncompahgre Project, Colo. 
 Fig. D. — Farmer water gates on concrete inclined slabs. Sun River Proj- 
 ect, Mont. 
 Plate IX .... .... 124-125 
 
 Fig. A. — ^Pumping water by wind miU into earth tank from which an 
 
 irrigating stream can be had. 
 Fig. B. — Gasoline pumping equipment. 
 Fig. C. — Generators driven by water power, furnishing electrical energy 
 
 for pumps, Minidoka Project, Idaho. 
 Fig. D. — Electrically operated centrifugal pumps delivering water to 
 
 laterals on Gila River Indian Reservation, Ariz. 
 Plate X . . . . . . 138-139 
 
 Fig. A. — Alkali flat, formerly a valuable farm, now ruined by careless 
 
 irrigation and lack of drainage. 
 Fig. B. — Distributory lined with concrete to reduce loss of water and 
 
 prevent development of alkali. 
 Fig. C. — Weir and self-registering gage, Williston Project, N. Dak. 
 Fig. D. — -Automatic gage for recording height of water in river or main 
 
 canal, Laramie River, Colo. 
 Plate XI . . . . ... 192-193 
 
 Fig. A. — Storage dam site, Roosevelt Dam, Salt River Project, Ariz. 
 
LIST OF PLATES xiii 
 
 Facing Page 
 Fig. B. — Drilling for bed rock at storage dam site, Shoshone Project, Wyo. 
 Fig. C. — Spillway of Bumping Lake dam, Yakima Project, Wash. 
 Fig. D. — Spillways of Roosevelt Bam, Salt River Project, Ariz. 
 Plate XII . 202-203 
 
 Fig. A. — Brush and stone dam, typical of pioneer conditions. Las Cruces 
 
 canal, Rio Grande Project, New Mexico. 
 Fig. B. — Log and earth dam, Cimarron River, New Mexico. 
 Fig. C. — Foundations for timber dam, Yakima Project, Wash. 
 Fig. D. — Apron of partly finished timber dam, Yakima Project, Wash. 
 Plate XIII . , 214-215 
 
 Fig. A. — Foundations for earth dam, showing excavations for puddled core 
 
 and earth being brought to the site by railroad train, then distributed 
 
 and rolled in thin layers, Umatilla Project, Oregon. 
 Fig. B. — Earth dam partly protected by heavy gravel on water side, 
 
 Boise Project, Idaho. 
 Fig. C. — Hydraulic construction of earth dam; giant in foreground wash- 
 ing earth and small rocks into flume supported on trestles and conveying 
 
 materials to site of dam, Okanogan Project, Wash. 
 Fig. D. — Completed dam built by hydraulic process. 
 
 Plate XIV . . . . . . 224-225 
 
 Fig. A. — Concrete core wall in earth dam, Carlsbad Project, New Mexico. 
 Fig. B. — ^Loose rock protection of earth dam on water side, Umatilla 
 
 Project, Oregon. 
 Fig. C. — Paving on water side of earth embankment, Belle Fourche 
 
 River, S. Dak. 
 Fig. D. — Concrete block protection against wave action on earth dam. 
 
 Belle Fourche Project, South Dak. 
 Plate XV . . . 234-235 
 
 Fig. A. — Earth and rockfiU dam under construction, with low concrete 
 
 core wall, gravel and earth is being dumped on upper side with loose 
 
 rock below, Minidoka, Idaho. 
 Fig. B. — Concrete structure for regulating floods, East Park dam, Orland 
 
 Project, Cal. 
 Fig. C. — Rubble masonry dam, lower portion of Roosevelt Dam, Arizona. 
 Fig. D. — Foundations for Lahontan Dam, Nev. View showing concrete 
 
 conduit, conveying water through lower part of dam, with conveying 
 
 plant in background. 
 Plate XVI . ... .... 252-253 
 
 Fig. A. — Gate tower and bridge from earth dam, forming Cold Springs 
 
 Reservoir, Umatilla Project, Oregon. 
 Fig. B. — Grillage protecting entrance to gates. Pathfinder Reservoir, 
 
 North Platte Project, Wyo. 
 Fig. C— Spillway with effective lengths increased by curved outlines, 
 
 Oreland Project, Colo. 
 Fig. D. — Spillway for earth dam, Belle Fourche Project, S. Dak. 
 
PRINCIPLES OF IRRIGATION ENGINEERING. 
 
 CHAPTER I 
 IRRIGATION 
 
 Definition. — Under the term "irrigation," as applied to agricul- 
 ture, is included all of the operations or practices in artificially 
 applying water to the soil for the production of crops. 
 
 Irrigation at the present time, considered from the standpoint of 
 the irrigation engineer, includes the conservation and storage of the 
 water supply, the carrjdng of water from the source of supply to the 
 irrigable area and distributing it to the lands. It involves, in many 
 cases, the development and bringing to the surface, waters from 
 underground sources, and also the raising of water by pumping or 
 other means to lands which cannot be reached by a gravity flow 
 from the source of supply. Closely related to irrigation is also the 
 question of drainage for the removal of excess waters from the land. 
 
 Draiaage, either by natural or artificial means, is equally as 
 important as irrigation to insure successful agricultural operations. 
 It is generally impracticable to apply water to lands sufficient to 
 grow crops without a portion of it being wasted either on the surface 
 or underground. This waste, or excess, must be removed either 
 through natural outlets or artificially constructed drainage ditches, 
 in order to prevent the land becoming waterlogged or charged with 
 alkali and rendered unfit for successful farming. 
 
 In addition to the physical problems involved in irrigation, 
 economic questions must also be considered. These questions in- 
 volve estimates on the value of lands to be irrigated and a comparison 
 of these values with the cost of constructing irrigation works in 
 order to determine whether the project is feasible from a financial 
 standpoint. 
 
 History and Development. — The practice of irrigation is older than 
 civilization. It origiaated doubtless in the semi-tropical and rela- 
 tively arid regions, where there is a periodic overflow of the desert 
 areas traversed by some of the large rivers like the Nile. These 
 streams, coming from plateau or mountain regions, are swollen by 
 seasonal rains or melting of snow. Mankind in the early stages of 
 
 1 
 
2 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 development learned to guide or assist this overflow by rough dikes 
 and rudely constructed ditches, later building canals to bring the 
 water out to lands which would not be overflowed naturally, and 
 thus gradually becoming independent of the natural rise of the 
 stream. Before historic times the practice of irrigation had been 
 recognized to such an extent that rules relating to the handling of 
 water were embodied in the earliest of known writings. In the code 
 of Hammurabi (2250 B. C.) it appears that provisions were made to 
 cover similar troubles and controversies that are being met to-day. 
 Laws concerning the distribution of water and guarding against waste 
 
 Fig. I. — Humid regions of the world, indicated in black; arid or non-productive 
 regions indicated by uncolored land areas. 
 
 or damage to a neighbor's field through carelessness may be copied 
 and applied to modem conditions from the oldest of recorded regu- 
 lations. In nearly all of the countries bordering the Mediterranean 
 and to the east in Mesopotamia, India and China, the art of irri- 
 gation was practised. The early writings on the discovery and con- 
 quest of Mexico and of South American countries casually mention 
 the irrigation canals as part of the features of the country. 
 
 The relative location and position of the arid regions of the world 
 are indicated by the black areas on the accompanying diagrammatic 
 map (Fig. i). This illustrates how small are these humid areas, 
 as compared with the total land surface enclosed within the outlines 
 and left blank as indicating conditions where plant life is dependent 
 
IRRIGATION 3 
 
 largely upon an artificial supply of water or where the cUmate is 
 too cold for the production of most of the ordinary crops. As in- 
 dicated on this diagram, the greater part of western Asia and the 
 Mediterranean countries within which civilization has developed 
 are arid or semi-arid; also the greater part of the western half of North 
 America including a considerable portion of Canada, Mexico, and 
 the United States. 
 
 In the southwestern portion of the United States, especially in 
 Arizona and New Mexico, remains of irrigation works have been 
 found which were constructed and operated prior to any recorded 
 history of that section. In the valley of the Rio Grande, irrigation 
 was practised by the native inhabitants before the advent of Spanish 
 explorers in the early part of the sixteenth century. The early 
 Spanish missionaries also constructed irrigation works in that valley 
 some time during that centiury. This, so far as known, was the begin- 
 ning of modern irrigation in the United States. Some of the works 
 constructed by the early Spanish settlers have been in use almost 
 continuously up to the present time. 
 
 In 1847, irrigation was begun by the Mormon settlers in the Salt 
 Lake Valley, Utah. This was the beginning of Anglo-Saxon irriga- 
 tion in this country. The next irrigation development of any mag- 
 nitude was about twenty years after work was started in Utah, 
 when it was taken up in Colorado and California. From these 
 parent colonies it gradually spread to the other states of the arid 
 west. 
 
 The first attempts at irrigation, as previously stated, were primi- 
 tive in character and consisted principally in assisting nature in 
 carrying water over the low bottom lands during the flood period. 
 The next step was the diversion of water from the streams and con- 
 ducting it by means of crudely constructed canals to the lands. The 
 first ditches constructed throughout the west consisted of simple 
 furrows for turning part of the flow of a creek to the low-lying bottom 
 lands. Diversion works, in many cases, consisted of temporary 
 dams of bags of sand placed in the stream to raise the water slightly 
 and divert it to the canals. When not in use, canals were frequently 
 closed by means of an earthen embankment. When water was 
 desired in the canal, the embankment was wholly or in part removed. 
 In the construction of these early canals engineering advice was 
 rarely sought, grades were fixed by the eye or by the flow of water 
 and locations made to conform to the contours of the slopes. 
 
 In general it may be said that the advances in irrigation, the oldest 
 
4 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of agricultural practices, have been made but slowly. It was not 
 until comparatively recent times that the larger problems pertaining 
 to storage and conservation of water supply were undertaken. 
 Within the past few years remarkable progress has been made in 
 this direction. The ultimate limit of the amount of land which can 
 be brought under irrigation in the arid west depends largely upon 
 the further conservation and storage of water supply and improved 
 methods of transporting, and applying it to the soil. 
 
 Needs and Benefits.- — The need of irrigation arises from lack of 
 natural rainfall at the times when required by crops. In some 
 regions the total precipitation annually is apparently adequate for 
 all vegetation, but frequently the rain occurs at seasons when it is 
 not needed and fails at critical times, thus irrigation must be prac- 
 tised during the season of summer drought. Under these conditions 
 it may be considered as a form of insurance, while in the truly arid 
 areas it is an absolute necessity. 
 
 The benefits which are derived from irrigation are those which 
 arise from the ability to supply the amount of water needed by the 
 growing plants in the quantity and at the times when it is most bene- 
 ficial in crop production. In the arid or dry regions where rainfall 
 is irregular or spasmodic there are consequently few clouds, the sxxn- 
 shine reaches the soil without obstruction and where water can be 
 suppHed this continuous unobstructed daUy sunshine stimulates 
 plant growth to a high degree, because of the well-known fact that 
 all life and growth on the earth is maintained by the sun's energy. 
 
 Irrigation affords ideal conditions for agriculture, since with the 
 life-giving sunlight and a means to supply moisture at proper times 
 and in the exact quantity needed, agriculture can be reduced more 
 nearly to scientific accuracy. 
 
 It is largely because of these facts that agriculture in an arid 
 region offers larger opportunities for returns from a given area than 
 in the humid regions, where dependence must be placed upon an 
 erratic rainfall. The amount of sunlight in the humid areas and 
 consequently the forces leading to growth are limited by the many 
 cloudy days. Ignoring this fact, it has sometimes been urged that 
 the same amount of energy and investment put in the agricultural 
 operations of the eastern part of the United States should be equally 
 or more productive than in the western, but, in this statement, 
 there is a neglect of consideration of this all-important item of total 
 amount of sunlight. 
 Methods of Irrigation. — Ordinarily, water for irrigation purposes 
 
Plate I 
 
 Fig. a. — Diverting dam in Boise River, Idaho, a typical structure for taking 
 out river water by gravity. 
 
 Fig. B. — Main northside canal of Minidoka Project, Idaho. Illustrative of the 
 lairger irrigation canals, with power transmission lines located on the bank. 
 
 ( Facing Page 4) 
 
Plate I 
 
 Fig. C. — Water being distributed to the fields through furrows after having 
 been diverted from the river by gravity canals. 
 
 Fig. D. — Water being applied to the fields by flooding. 
 
IRRIGATION 5 
 
 is conducted from some stream or lake by means of open canals dug 
 in the rocks or earth, similar in many respects to the drainage ditches 
 commonly used in humid regions. In fact, the resemblance between 
 the irrigation canal and a drainage ditch is so great that the word 
 "ditch" is commonly applied to the small irrigating canal, a:lthough 
 it is preferable to limit the word "ditch" to its original application 
 in drainage. 
 
 The main canal, designated to bring water to a given area, heads 
 usually in some perennial stream and takes water from it either by 
 means of a dam or obstruction in the river, forcing some of the water 
 into the canal (see Plate I, Fig. A) or the water is diverted by build- 
 ing the inlet gates at a level sufficiently low to permit it to flow from 
 the stream into the head of the canal. From this point the canal is 
 built on a gently descending grade less than that of the stream from 
 which a supply is derived, that is to say, if the stream falls at a rate 
 of lo ft. per mile, the irrigating canal may be built with a fall say i ft. 
 per mile and at the end of lo miles the canal will be 90 ft. above the 
 bed of the stream. To build such a canal in ground which will sus- 
 tain it, the canal after bordering the stream for a short distance 
 must turn from it, skirting the valley and thus partly surrounding 
 a considerable body of land which becomes wider and wider between 
 the canal and the river. Water released from the canal will flow 
 down the natural drainage lines back to the river, or it can be kept 
 up on the higher ridges and thus brought to the highest points of 
 most of the farms between it and the river. 
 
 The canal divides or sends off branches and these again send from 
 their sides other smaller branches, sometimes called laterals, dividing 
 and the sub-dividing until each farm is reached. (See Plate I, Figs. 
 C and D.) 
 
 Earthen canals necessarily lose a considerable amount of water by 
 percolation or seepage into the soil, especially if this is sandy or 
 gravelly. There are also small losses by evaporation from the sur- 
 face. Where water is very valuable the loss by percolation is fre- 
 quently reduced by lining the canals with masonry or other imper- 
 vious materials, or by confining the water in pipes as is the case of 
 city supply. 
 
 Water having been brought to the area to be irrigated, there are 
 a variety of ways in which it is applied to the land. One of the com- 
 mon methods, ordinarily known as "flooding," is to deliver the water 
 to the highest portion of the land and allow it to flow downward 
 over the slope until the entire area or field to be irrigated has been 
 
6 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 covered. (Plate I, Fig. D.) Another method, sometimes called the 
 "check system," requires that the land be divided into small areas, 
 each surrounded by a check or border of earth a few inches in height. 
 Water is turned into each of the small areas until it is covered to the 
 required depth. This method has advantages over ordinary flood- 
 ing in that the amount of water applied to each portion of the land 
 can be more accurately controlled. In the "furrow system," water 
 is carried over the land in small furrows (Plate I, Fig. C), excavated 
 by means of a plow or other suitable appliance, a few feet apart over 
 the entire area. Still another method, known as "sub-irrigation," 
 consists in bringing the water below the surface by means of pipes 
 laid in the soil and allowing it to esc^ape through small openings in 
 the walls of the pipes. This method, while theoretically nearly 
 perfect, is ordinarily prevented by the excessive cost. 
 
 Comparison of Irrigated and Non-irrigated Lands. — The advant- 
 ages of irrigation are best expressed in values of crops per acre on 
 irrigated and non-irrigated areas. Unfortunately it is difficult to 
 make a comparison of this kind on account of the lack of comparable 
 data relative to crop values in different sections of the country. 
 There are examples where special crops grown without irrigation 
 have yielded greater returns per acre then other crops grown with 
 irrigation. There are few if any examples, however, where non- 
 irrigated orchards have been known to produce crop retiu-ns equal 
 to those under irrigation. The same may also be said of the more 
 staple farm crops and especially is it true for vegetables and what is 
 known as truck farming. 
 
 In general, it is believed that in a well-irrigated region the values 
 of ordinary farm crops are from 50 to 75 per cent, greater than in 
 an equally well-farmed section of the humid region. Evidence of 
 this fact is shown by the relative land values upon which the crops 
 are made to pay returns, and the size of farms required to support 
 a family. 
 
 The difference in value is particularly marked in the case of the 
 more valuable fruits because of the fact that with complete regula- 
 tion of the water supply the size and quality of the fruit may be more 
 closely controlled. This same condition appUes also, but possibly 
 in a somewhat less degree, to the growing of forage, vegetables and 
 other staple crops. Irrigation consequently offers possibihties of 
 intensive argiculture and of dense population, such as is not practi- 
 cable where dependence for a water supply must be placed upon 
 rainfall. 
 
IRRIGATION 7 
 
 In making a comparison of the values of products from an irri- 
 gated and non-irrigated region, it must be assumed that equal skill 
 and energy is involved and that the cost of labor, means of transpor- 
 tation and character of markets are approximately the same. Even 
 with this assumption,, which is in many cases less favorable to the 
 irrigated areas, they generally show larger average crop returns. 
 
 It is frequently the case that farmers practising irrigation are 
 doing so without the long experience which has been had in the humid 
 regions. Most of them have come from regions where dependence 
 is placed in rainfall and many of them must unlearn the practices 
 laboriously acquired and handed down for generations in order to 
 make a success of irrigation farming. Others are men with but 
 limited experience in agriculture who must pay for the experience 
 they acquire by occasional failure. 
 
 Irrigation in many parts of the United States is still in a pioneer 
 condition so that the averages of productions are not fairly compa- 
 rable with those from the older humid regions. This is in part on 
 account of the soil not being fully subdued and brought to the point 
 where large crop returns can be expected, and partly on account of 
 the lack of means by the settlers to carry on operations in the most 
 efficient manner. 
 
CHAPTER II 
 IRRIGABLE LANDS 
 
 Arid Region. — In the arid regions are the best and largest ex- 
 amples of irrigation, as here it is a necessity, while elsewhere it is 
 more of the nature of an insurance for crops. The arid regions of 
 the United States are part of those of the North American Con- 
 tinent which extend from about Central Mexico northerly in a 
 widening belt across the United States and into Canada. They are 
 generally defined as the localities having less than 15 inches of 
 annual rainfall. They consist for the most part of elevated plateaus 
 or broad valleys broken by mountain ranges, the higher slopes of 
 which have a humid climate. Thus the arid regions are not contin- 
 uous, but are interspersed with areas of humidity, from which come 
 the streams so essential in irrigation development. 
 
 Aridity is a consequence of the continental structure and is a 
 resultant of the atmospheric circulation of the globe, which cannot 
 be controlled or modified in any appreciable degree by the work of 
 mankind. It has been the dream of all the ages that mankind might 
 influence the distribution and quantity of rainfall, primarily by 
 occult or supernatural agencies, by incantations and various cere- 
 monies. The later manifestations of this hope have been in the 
 efforts to bombard the heavens, and by concussions resulting from 
 great explosions to bring about the production of rain. It has 
 also been hoped from a more rational standpoint to modify the 
 quantity of precipitation by preserving or increasing the forest 
 cover on the uplands. All of these have failed, and there is now a 
 more general recognition of the fact, as before stated, that the 
 formation of rain is due to world-wide rather than to local conditions. 
 
 Roughly speaking, it may be stated that the arid regions of the 
 United States lie from about 102nd meridian west of Greenwich, or 
 about the western limit of Kansas, westerly to the Pacific Coast, 
 in southern California, and to the Cascade Ranges of northern 
 California, Oregon and Washington. To the west of these, the 
 humidity is great and it thus happens that in the state of Washing- 
 ton there is extreme aridity on the east of the mountains and equally 
 extreme humidity to the west of them. 
 
 8 
 
IRRIGABLE LANDS 9 
 
 As before stated, there are scattered through this vast arid region 
 considerable areas of relatively humid mountain masses, especially 
 in northern portion of western Montana and in northern Idaho. 
 The relative position and extent of the arid, semi-arid and humid 
 regions of the United States are shown in Fig. 2. 
 
 To the east of the truly arid region is a broad belt of country, several 
 hundred miles in width, with progressive decrease from the extreme 
 aridity of the high plains to the moderately humid conditions of 
 the lands of the Mississippi Valley. This broad belt is by no means 
 fixed, as in some seasons when the rainfall is deficient, the arid or 
 
 Fig. 2. — Map showing relative area and position of arid, semi-arid and humid 
 regions of the United States. 
 
 semi-arid conditions progress to the eastward and again retreat 
 with the non-periodic fluctuations or successions of wetter seasons. 
 Thus there is a broad belt of country of which western Kansas is 
 tjrpical, having a soil of exceptional fertility, one which has not 
 been washed by the rains, but which has alternately a climate too 
 dry for successful production of ordinary crops, followed by years of 
 conditions highly favorable for profitable agriculture. These are 
 the conditions which lead to what is sometimes known as the famine 
 regions of the world, where the richness of the soil tempts agricul- 
 ture, and where successive years of moderate precipitation en- 
 courages the development of population to be followed by dry years 
 with resulting poverty and suffering. 
 
10 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 Topographic Features. — The arid region of the United States as a 
 whole is relatively high, including as it does the great plateau of 
 the Rocky Mountains or Cordilleran area. The general slope from 
 about the center of the region toward the south is such as to bring 
 the arid lands down to or even below sea level, as in the case of Death 
 Valley and the Salton Desert in southern California. Toward the 
 north there is also a general decline in altitude, but far less marked 
 than toward the south. The climate of the northern portion of 
 this arid region is modified and less rigorous on account of this de- 
 scent toward sea level. 
 
 The mountain masses which traverse the arid regions serve to 
 force upward the prevailing winds, causing them to deposit their 
 moisture on the slopes. These have a relatively heavy precipitation 
 as testified by the presence of the forests which extend from the 
 timber line well down the sides toward the dry valleys. These 
 forests for the most part have been segregated from the public 
 domain of the United States and set aside as reservations or National 
 Forests (see Fig. 3) under the charge of the Forest Service of the 
 Department of Agriculture. The primary object of creating these 
 reserves has been for the protection of the timber supply of ths coun- 
 try, but a secondary and sometimes more important object to be 
 attained is the beneficial effect which forest cover has on the water 
 supply so necessary for agricultural development in the valleys. 
 
 These scattered mountain ranges and isolated peaks, thus give 
 rise to innumerable streams, some of considerable size. These 
 coming with steep slopes toward the valleys render the conditions 
 favorable for economical development of irrigation. In Utah, for 
 example, the almost innumerable small streams from the Wasatch 
 Mountains issuing upon the desert valleys at frequent intervals, 
 enabled the pioneers to build their small irrigation canals at the 
 minimum of cost. Relatively few large structures were required 
 and the steep slopes permitted the water to be carried out in narrow 
 channels but still at a sufficient elevation to cover the irrigable lands 
 in the valleys below. 
 
 The Soil. — The soil of the arid regions differs essentially from that 
 of the humid regions in that disintegration has taken place under 
 conditions where the earthy salts have not been so completely 
 leached out. Many of the soils have been built up by wind action, 
 others are alluvial or delta deposits brought out upon the margin 
 of the valleys by the streams issuing from the high mountains. 
 Still others have resulted from sedimentation in fresh-water lakes. 
 
IRRIGABLE LANDS 
 
 11 
 
12 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 As a whole, the soils are more highly productive in their natural 
 condition than those of the humid regions, excepting possibly those 
 of the swamp lands. 
 
 One of the most notable characteristics of the agricultural soils 
 of the arid region is the deficiency of organic vegetable matter. The 
 first effort of the skilled irrigation farmer is to supply this lack. 
 Fortunately, alfalfa, one of the most valuable of the forage plants, 
 is also valuable for supplying organic matter to the soil. This 
 plant also has the property of obtaining nitrogen from the air, and 
 giving it to the soU, through the activities of bacteria which inhabit 
 nodules on the roots. As soon, therefore, as the soU has been broken 
 up and partly subdued by planting a grain or similar crop, alfalfa 
 is put in and after a few cuttings the green plants are plowed under, 
 thus supplying the soil with the necessary organic matter, and mak- 
 ing it capable of producing subsequently large crops of potatoes, 
 sugar beets, or other vegetables. 
 
 Preparation of Lands. — The first and most important step in 
 preparing the lands for irrigation is to smooth and level the surface 
 as accurately as possible. If this is once properly done, it will be 
 possible to till the soil year after year, and apply water with a mini- 
 mum amount of labor and loss. If it is not carefully performed 
 there will always be difficulty in thorough irrigation with resulting 
 uneven growth of plants due to the fact that water has been applied 
 more plentifully in some spots than in others. 
 
 In its native state, most of the best agricultural land is covered 
 with sagebrush. Other lands have the so-called greasewood or 
 similar desert vegetation, nearly all of which is easily removed by 
 dragging with a heavy iron bar or by using heavy machines made 
 especially for the purpose. Having removed the sagebrush, the next 
 step is to break up the ground with a plow, and then, as above stated, 
 to smooth and level it into srtiall fields or "lands," using for this 
 purpose a scraper or drag by which the higher knolls are shaved off 
 and the depressions filled. 
 
 Where heavy winds prevail, especially in the spring, particular 
 care must be taken not to remove at once all of the sagebrush or 
 other desert vegetation, because by so doing the winds have access 
 to the loose soil and readily blow it away, cutting out the seed or 
 young plants. By leaving rows of sagebrush across the path of the 
 wind and cultivating the intervening strips, the surface is protected 
 until the plants thoroughly shade the ground; it is then possible to 
 take out the windbreaks and cultivate the remaining soil. By the 
 
IRRIGABLE LANDS 13 
 
 exercise of skill and forethought it is thus possible to get into crop 
 lands which otherwise could not be handled. After the first few 
 years of cultivation, especially after a certain amount of vegetable 
 matter is gotten into the ground, the tendency of the soil to be moved 
 by the wind is greatly decreased and by planting trees for windbreaks 
 and taking other precautions, the difficulties encountered by the 
 pioneers are successfully overcome. 
 
 Location. — There is more land than water with which to irrigate 
 in most parts of the arid region. For a given water supply there is 
 usually possible a choice of lands not merely with reference to physical 
 characteristics but with regard to accessibility to markets or lines 
 of communication. The arid region, as a whole, is sparsely popu- 
 lated, there being few notable cities, but with the development of 
 the railroad systems, it is now possible to reach nearly all the irrigable 
 lands with relatively short wagon roads. Much of the success of 
 any irrigation project depends upon the choice of lands in such way 
 that the distance to markets and cost of transportation will be as 
 small as possible. 
 
 The west is favored in the fact that the precious minerals are quite 
 widely disseminated and at the mining camps there is usually an 
 excellent market for everything which can be raised under irrigation. 
 In fact the two occupations are interdependent in that the develop- 
 ment of agriculture in the vicinity reduces the cost of living and 
 consequently the cost of mining, so that the lower-grade ores can be 
 handled and the development of these mines gives a needed market 
 for the crops. 
 
 Intensive Farming. — The large amount and intensity of degree of 
 the sunlight and favorable condition of soil as compared with the 
 humid regions render it possible for the average farmer to be sup- 
 ported on a much smaller tract of land than is the case in the non- 
 irrigated portions of the United States. The expense of building long 
 lines of canals results also in bringing the farms close together and 
 in utilizing to the fullest extent possible all the lands within a given 
 district. The irrigated areas are not only capable of the most 
 intensive cultivation but all of the conditions of water supply and of 
 transportation favor the most complete development. 
 
 The high price of labor which prevails through the western part of 
 the United States results in the greater part of the work on each farm 
 being performed by the family living upon it, and this in turn tends 
 to keep down the area of each farm and increase the economics and 
 the product per acre. As time goes on, with greater increased ca- 
 
14 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 pacity for production and with growth of population, the farms are 
 further sub-divided; there is a marked tendency toward still more 
 intensive cultivation and with corresponding increase in values the 
 occupation of smaller and smaller areas per family, the standard of 
 living increasing with the higher productivity of soil. 
 
 Climate. — The climatic conditions are those generally known as 
 continental and are correspondingly extreme with cold winters and 
 hot summers. The dryness of the air renders these extremes of tem- 
 perature less burdensome than they would be in more humid portions 
 of the country. The summers, with their continuous daily sunshine, 
 even though relatively short in the north, are conducive to large crop 
 production. In the southern portion of the arid regions, for example 
 in Arizona, crop growth continues practically throughout the year, 
 there being hardly a perceptible rest of plant activity during the 
 winter, so that crop follows crop in succession as rapidly as it can be 
 matured and removed. As far as human health is concerned and 
 that of domestic animals, the extreme aridity seems to be highly 
 beneficial and is in general recommended. 
 
CHAPTER III 
 WATER SUPPLY 
 
 Source of Water Supply. — The principal source of water supply for 
 irrigation is from the perennial streams which issue from the higher 
 mountains. A relatively small but increasingly important amount 
 of water is derived from floods which are held in reservoirs and a still 
 smaller proportion from natural storage in the ground, the water 
 being recovered by wells sunk in the gravels or sands of the valleys. 
 
 The streams which have their source in the high mountains are 
 maintained not only by the rainfall on the mountain sides but are 
 increased in volume by the melting snows. With their large supply 
 from the forested areas they are the most nearly ideal for purposes of 
 irrigation. The annual floods occur at a nearly definite date and it is 
 possible to plant crops with reasonable assurance of an adequate 
 amount of water for ordinary irrigation. These are the sources of 
 supply which have been first utilized and which are now in many 
 instances over-appropriated, that is to say, the claims for use of water 
 aggregate more than the usual flow. 
 
 In distinction from mountain streams are those which have a less 
 elevated catchment area, and which depend for water upon the less 
 regular rainfall. These are occasionally in flood but for the greajter 
 part of the year are nearly or quite dry and cannot be depended upon. 
 Irrigation has been tried along these streams and considerable in- 
 vestment made but with little success, as the headworks are fre- 
 quently washed out by the erratic floods, and before they can be 
 restored the stream has usually gone dry. In nearly every case it is 
 necessary to provide, wherever possible, large and expensive reser- 
 voirs out on the plains in order to regulate the supply. Even then 
 there is considerable uncertainty owing to the fact that the rainfall 
 in these lower regions is not as uniformly distributed as it is on the 
 higher summits. 
 
 Character of Supply. — From what has been stated, it is apparent 
 that there is a very great difference in the amount and reliability 
 of supply to be had from different streams. Those coming from the 
 mountains with forested and lofty catchment areas afford the fewest 
 
 15 
 
16 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 problems, as their flow is relatively steady, while those coming from 
 lower and more open regions offer increasingly diflScidt questions, 
 and necessitate the careful study of all opportunities for providing 
 storage reservoirs. 
 
 The accompanying diagrams. Fig. 4 and Fig. 5, illustrate the differ- 
 ence in behavior of tj^ical rivers of the eastern humid part of the 
 United States, and of the western arid portion. In Fig. 4 is indicated 
 by the position and height of the black areas the relative quantity 
 of water expressed in cubic feet per second or second-feet, occurring 
 throughout the year. The diagram illustrates the fact that the 
 greater portion of the water in the Susquehanna River at Harrisburg, 
 Pa., occurs in the spring, with summer drought, most notable in the 
 latter part of August, and early in September. In the case of the 
 Yadkin River at Salisbury, N. C, the greater portion of the water 
 occurred in short quick floods in the latter part of the summer and 
 early in the autumn, these being the result presumably of heavy 
 storms on the mountains. 
 
 In comparison with this is the diagram for the Gila River at 
 Buttes, Ariz., showing a very small relatively steady flow during the 
 early part of the year followed by erratic floods due to so-called 
 "cloud bursts" on the drainage basin. In marked contrast to this 
 is the large comparatively uniform flood in the Green River at Blake, 
 Utah, typical of the streams which come from the snow-clad moun- 
 tains, the water being supplied by the melting of the snow as sum- 
 mer advances. 
 
 A record of the behavior of the streams of the arid region, as well 
 as those of the humid region, has been undertaken by the United 
 States Geological Survey and beginning in about 1888, systematic 
 observations have been conducted on many rivers and creeks. It 
 has not been possible to measure aU of the flowing waters, but the 
 attempt has been made to select typical streams which would be 
 fairly representative of others in the vicinity. 
 
 The height of water at selected points has been observed and re- 
 corded day by day, and the quantity of flow corresponding to the 
 various heights has been ascertained. By means of these data it has 
 been possible to compute the total flow at the observed points by 
 months and seasons, giving figures of the amount and duration of 
 floods and of the low-water periods. 
 
 Benefits of Control. — The benefits which arise from the ability 
 to store these flood or waste waters need hardly be enumerated. 
 These waters unregulated frequently occur in quantity sufficient to 
 
WATER SUPPLY 
 
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18 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 destroy bridges, dams and other structures along their course or to 
 overflow the farms and villages on the lowlands. By holding back th 
 floods, which if unregulated would be a source of destruction, it is 
 possible to use this water in the reclamation of waste and useless 
 land and thus provide opportunities for citizens and their familier 
 who otherwise would not be able to obtain a foothold on the land. 
 From the standpoint of the stability of the commonwealth, there is 
 perhaps no engineering or economic operation which has a deeper 
 significance or is of greater value than this practical application of 
 the principles of conservation. 
 
 By a study of the data obtained from systematic measurements 
 it has been possible to arrive at certain conclusions with reference 
 to the practicability of conserving the waste waters and holding 
 them wherever suitable natural basins can be found, the outlet 
 of which may be closed by dams at reasonable cost. The Federal 
 Government, as the original proprietor and still the owner of vast 
 tracts of desert land, is interested in obtaining all of these facts 
 upon which engineering operations may be based and by which 
 money may be safely invested in the construction of storage works 
 for holding the flood waters and for delivering them at the proper 
 time to the lands which may be irrigated. 
 
 Study of Water Supply. — In the study of the water supply and 
 the practicability of storing or diverting it, the principal features of 
 importance are the daily or periodic observations of quantities. 
 From these a great variety of facts relative to the amount of water 
 available from a given stream may be secured and comparisons 
 made. At the same time it is important to obtain definite knowledge 
 concerning the topography of the catchment area from which the 
 v/ater flows, and to know its cultural conditions, and whether these 
 are likely to be changed in such way as to modify the amount of 
 water available. One of the important factors in a water supply is 
 its constancy or regularity of flow. In order to determine this it is 
 necessary to have records extending over a period of years. 
 
 In choosing a water supply, preference should be given to one 
 which is constant in character rather tnan one which varies greatly 
 from year to year, even though the total flow from the constant 
 source is somewhat the smaller. 
 
 Rainfall. — The primary factor in questions of water supply is the 
 amount of precipitation in the form of rain or snow which reaches 
 the earth. This varies greatly in different parts of the country, 
 being governed quite largely by geographic or topographic relations. 
 
WATER SUPPLY 
 
 19 
 
 Without entering into detailed discussion of these, it is sufficient to 
 call attention to the result as illustrated by the accompanying map 
 (Fig. 6), showing that there is a wide divergence in the total quantity 
 of precipitation in different parts of the United States, the greatest 
 rainfall being on the eastern coast and near the Gulf of Mexico and, 
 on a comparatively narrow strip of country adjacent to the Pacific 
 Ocean in the extreme Northwest. The least amount of rain which 
 occurs is that within the interior of the country which includes a 
 considerable portion of what now forms the states of Nevada, Utah, 
 New Mexico, Arizona, and adjacent portions of California. 
 
 ■^^!^>(:& 
 
 /-32~---' 
 
 % 
 
 
 Vv- 
 
 Fig. 6. — Map showing mean annual rainfall of the United States. 
 
 The above map shows in a general way the inequalities of distribu- 
 tion throughout the surface of the country being the averages of 
 observations carried on through many years. For any single 
 locality there is great divergence; during one year there may occur 
 nearly twice as much rainfall as during some preceding or succeeding 
 year. This is illustrated by the diagram Fig. 7 of the annual pre- 
 cipitation at Salt Lake City, Utah, where the average is about 16 
 inches, with few years which approximate this amount. 
 
 Attempts have been made to arrive at some rule or generalization 
 regarding this irregularity of rainfall; efforts have been made to 
 connect it with the occurrence of the sun spots and other natural 
 phenomena. Various students have figured out, to their own satis- 
 
20 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 faction, that years of drought or flood occur with a certain general 
 regularity in cycles of 7 years, or 11 years, or 17 years, but hardly 
 any two of these persons will agree as to the actual facts or conclu- 
 sions to be drawn from them. For most practical piu-poses, atten- 
 tion should be concentrated on the fact that whenever a relatively 
 dry year occurs, it may be followed by an even greater drought and 
 provision must, therefore, be made to meet a succession of relatively 
 dry years. 
 
 
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 1 
 
 
 1 
 
 
 
 
 1 
 
 1 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 .... 
 
 §§§§^||||||||||||§|||||§|§§§||. 
 
 Fig. 7. — Diagram of annual precipitation at Salt Lake City, Utah, illustrating 
 the fluctuations in total quantity of rainfall. 
 
 Runoff. — The term "runoff" was devised as a convenient 
 expression for the water which flows off the surface of the land 
 in the form of visible streams. The relation between the 
 amount of water which falls upon the land in the form of rain or 
 snow and the amount of runoff which may become available for 
 irrigation has been a source of investigation and controversy among 
 engineers. The inference war, drawn by some engineers and physi- 
 cists, from early observations on rainfall and runoff, that a some- 
 what definite relation existed between them and that by knowing 
 the rainfall the amount of runoff could be calculated. The results 
 
WATER SUPPLY 21 
 
 which have followed from this theory have been highly interesting 
 but in many cases widely at variance with actual conditions. 
 
 On certain of the watersheds in the eastern and more humid 
 regions of the United States, where the rainfall is relatively constant 
 in amount and time of occurrence, there seems to be a relatively 
 consistent ratio between the rainfall and runoff. In the arid west 
 this does not appear to exist and attempts to apply the ratios found 
 in the humid regions of the east to the arid regions of the west 
 produce misleading and, in many cases, ludicrous results. A case 
 illustrating the above remarks is that of an engineer acquainted 
 with eastern conditions only who was employed to investigate the 
 water supply available from an Arizona river. By taking the rain- 
 fall of the area and using what he considered a conservative allow- 
 ance, namely, about 20 per cent, for runoff, he reached the conclusion 
 that a certain amount of water would be available. It so happened 
 that measurements had already been made which showed the runoff 
 to be a little more than 2 per cent, of the rainfall. The engineer in 
 question was very sure that there must be an error in printing 
 the records of stream flow, since his careful analysis had demon- 
 strated to him that the water which theoretically would be available 
 was ten times that found by direct observation. 
 
 Influences affecting Runoff. — A clear conception of the varying 
 character of runoff can be obtained by considering it as the excess 
 of water on a given area after all of nature's requirements for 
 moisture on that area have been supplied. It is the balance, so to 
 speak, between nature's supply and immediate needs. If no more 
 water falls on a given area than can be taken up and absorbed by 
 it the resulting runoff will be nil. The time allowed for water to 
 be taken up either through the soU or the atmosphere, as will be 
 seen later, also plays an important part in determining how much 
 will be absorbed and how much will be carried away by streams. 
 
 The principal factors which affect directly the amount of runoff 
 are: amount and character of rainfall, character of watershed, 
 and evaporation. All of these are varying influences of so com- 
 plex a nature that it is impossible to determine any accurate measure 
 of their value. It is possible in some cases to find watersheds where 
 conditions will give nearly the same amount of runoff on each of 
 them. Where this is the case, an estimate of the runoff from an 
 unknown area may be obtained by comparing it with that of a 
 similar area where measurements have been made. 
 
 The first and most important consideration for runoff is rainfall. 
 
22 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 It does not follow, however, that rainfall always produces runoff. 
 It is a significant fact that a certain amount of rainfall is required 
 before any runoff will result. This minimum amount will vary for 
 different watersheds and climatic conditions. It is also true that the 
 ratio of runoff to rainfall increases with the rainfall. The first ques- 
 tion then is whether- the total rainfall on a given area is suflacient to 
 produce any appreciable runoff. Granting that this be the case, the 
 next question is to determine what amount of runoff may be expected. 
 
 If the rainfall occurs in heavy, copious showers, so that only 
 a small amount has time to soak into the soil, the greater part may 
 be carried away over the surface and eventually be collected in 
 the streams below. The same amount of rainfall occurring in a slow 
 steady drizzle may be entirely absorbed by the soil and add nothing 
 to the stream flow. If precipitation comes in the form of snow and, 
 as is frequently the case, is banked up in the ravines, it may be held 
 well into the summer months, acting in the meantime to supplement 
 the stream flow at a more or less uniform rate. 
 
 Character of Watershed. — The steepness of the slopes, kind and 
 depth of soil, and the presence of vegetation upon a watershed will 
 influence in a marked degree the amount of runoff. Where water 
 falls upon steep slopes it flows away rapidly and before a large 
 part of it can be absorbed by the soil. Even when the soil becomes 
 saturated to some depth through long-continued rains the steep 
 slopes permit more rapid drainage and it results that a greater 
 amount of water is carried away from them than would be the case 
 on flat slopes otherwise similar in character. A rainfall giving as 
 high as 30 or 40 per cent, runoff on the steep sides of a mountain 
 range may not produce more than 3 or 4 per cent, on the lower 
 level or gently rolling plains. 
 
 A deep porous soil will absorb and hold more water than a shallow 
 compact one. On rock slopes practically no water is lost by absorp- 
 tion, hence greater runoff results from them than from earthen 
 slopes. The presence of frost in the ground also tends to increase 
 the amount and rate of runoff. 
 
 The flow of water is retarded if the ground is covered by a forest 
 or other form of vegetation. More water will consequently sink 
 into the soil under these conditions than will be the case on land de- 
 void of vegetation. The presence of a forest cover also modifies the 
 rate of runoff by holding back a part of the waters and permitting 
 them to slowly trickle down to the streams. For this reason it is of 
 value in reducing the intensity of the flood flow after severe storms. 
 
WATER SUPPLY 23 
 
 Evaporation. — The greatest influence affecting runoff is evapor- 
 ation. Its action is continuous from every part of a watershed 
 where moisture is exposed to the atmosphere. Vegetation, wherever 
 present, and capillary action in the soil are constantly bringing 
 moisture to the surface of soils where it is changing to vapor. The 
 action of evaporation, while ordinarily continuous in character, 
 nevertheless varies greatly in amount at different times and in differ- 
 ent localities. 
 
 The rate of evaporation depends primarily upon the capacity 
 of the atmosphere to take up moisture and the ability of the surface 
 to supply this moisture as rapidly as it can be absorbed. The capac- 
 ity of the atmosphere to receive and dissipate moisture depends 
 upon temperature, rate of wind movement and the degree of satura- 
 tion or amount of water which it already contains. The rate at 
 which the soil can supply moisture depends primarily upon the depth 
 to water and the capillary action of the soil in bringing this water 
 to the surface. 
 
 AVhere water stands on the surface or where the surface layer of 
 the soil is saturated, the earth can supply moisture at a greater rate 
 than the air can absorb it. This condition exists on the surface of 
 lakes and ponds and upon land immediately after a rain. If the 
 surface supply is not replenished by frequent rains the moisture 
 disappears partly by seepage downward and partly by evaporation 
 until a condition exists where little or no water will be supplied to 
 the air. This is frequently the case in the extreme arid regions. 
 The rate of evaporation for a short period after a storm may be very 
 rapid but practically negligible for the remainder of the year. In the 
 humid regions, where the surface of the soil is moist during the greater 
 part of the year, the annual loss by evaporation is relatively constant. 
 
 It is evident that for a watershed from which there is no under- 
 ground flow, the runoff is equal to total rainfall less evaporation. 
 Such conditions apply closely on a large area where the underground 
 losses, if any, from it are so small as to be negligible when compared 
 with the total amount of water which falls on the area. On small 
 areas of a few hundred square miles and from which the underground 
 flow may amount to several per cent, of the rainfall, it is evident 
 they do not apply. 
 
 Runoff on Different Watersheds. — ^As illustrating the difference 
 in amount of runoff from different watersheds in various parts of 
 the United States, the following table is presented. This table has 
 been prepared from the records of stream gagings made by the 
 United States Geological Survey: 
 
24 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 MEAN ANNUAL RUNOFF FOR VARIOUS WATERSHEDS IN THE UNITED 
 
 STATES 
 
 River 
 
 Point of measurement 
 
 Drainage 
 
 area 
 
 square 
 
 miles 
 
 Period 
 
 Runoff in 
 depth in 
 inches on 
 
 drainage 
 area 
 
 Kern 
 
 Bakersfield, Cal 
 
 2,340 
 
 I 896-1905 
 
 4.36 
 
 
 
 
 San Joaquin 
 
 Hemdon, Cal 
 
 1,640 
 
 1896-1901 
 
 20.47 
 
 
 
 
 Kings 
 
 Sanger, Cal 
 
 1,740 
 
 1897-1906 
 
 20.38 
 
 
 
 
 Sacramento 
 
 Red Bluflf, Cal 
 
 4.300 
 
 1902-1906 
 
 24.06 
 
 
 
 
 Umatilla . . 
 
 Umatilla, Ore 
 
 2,130 
 
 Nov. 1, 1900, to 
 Dec. 31, 1900 
 
 3.94 
 
 
 
 Willamette 
 
 
 4,860 
 
 Jan. i, 1899. to 
 Dec. 31, 1908 
 
 46.62 
 
 
 
 
 Boise 
 
 Boise, Idaho' 
 
 2,610 
 
 1895-1904 
 
 IS 60 
 
 
 
 Green 
 
 Green River, Wyo 
 
 7,450 
 
 May I, 1896, to 
 Oct. 31, 1906 
 
 4.81 
 
 
 Laramie 
 
 Uva, Wyo 
 
 3,180 
 
 May, 189s, to 
 Oct., 1903 
 
 1. 10 
 
 Red 
 
 Grand Forks, N. Dak.. . 
 
 25,100 
 
 Sept., 1902, to 
 Sept., 1908 
 
 
 
 
 Rio Grande 
 
 Rio Grande, N. Mex.... 
 
 14,000 
 
 Jan. 1, 1896, to 
 Dec. 31, 1905 
 
 1.46 
 
 Animas . 
 
 Durango, Col 
 
 812 
 
 July, 1895, to 
 Dec, 19OS 
 
 14-86 
 
 
 
 South Platte 
 
 
 3.840 
 
 Jan. i, 1896, to 
 Nov. 30, 1906 
 
 1.44 
 
 
 
 Green 
 
 Greenriver, Utah 
 
 38,200 
 
 Jan., 1895. to 
 Dec, 1908 
 
 3.17 
 
 Logan 
 
 Logan, Utah 
 
 218 
 
 1896-1900 
 1904-1906 
 
 21.18 
 
 
 
 988 
 
 Nov., 1900, to 
 Dec, 1906 
 
 6.25 
 
 
 
 
 
 
 1,520 
 
 Sept., 1899, to 
 Dec, 1906 
 
 
 
 
 
 
 
 13.800 
 
 Jan., 1897, to 
 Dec, 1906 
 
 
 
 
 
WATER SUPPLY 
 
 25 
 
 MEAN ANNUAL RUNOFF FOR VARIOUS WATERSHEDS IN THE UNITED 
 STATES — Continued. 
 
 River 
 
 Point of measurement 
 
 Drainage 
 area 
 square 
 miles 
 
 Period 
 
 Runoff in 
 depth in 
 inches on 
 drainage 
 area 
 
 
 
 22S.000 
 
 Jan., 1902, to 
 Dec, 1906 
 
 I. IS 
 
 
 
 
 St. Croix 
 
 St. Croix Falls, Wis 
 
 6.370 
 
 1902-1904 
 
 
 
 
 Menotninee 
 
 Iron Mountain, Mich... 
 
 2.420 
 
 Sept., 1902, to 
 Sept., 1906 
 
 18.92 
 
 
 Peoria, 111 
 
 13.200 
 
 Apr. I, 1903. to 
 Jan. 30, 1906 
 
 14.11 
 
 
 
 
 
 Waterville, Ohio 
 
 6,110 
 
 Dec, 1898, to 
 Jan., I go 2 
 
 
 
 
 Scioto 
 
 Columbus, Ohio 
 
 i.oso 
 
 1899 to 
 July, 1906 
 
 10.43 
 
 
 
 Duck . . 
 
 Columbia, Tenn 
 
 1,260 
 
 Nov. 1, 1904, to 
 Dec 31, 1908 
 
 18.87 
 
 
 
 
 Chattanooga, Tenn 
 
 21,400 
 
 1899-1908 
 
 
 
 
 Tombigbee 
 
 Columbus, Miss 
 
 4,440 
 
 1905-1908 
 
 15.48 
 
 
 
 1.900 
 
 1900-1908 
 
 
 
 
 
 
 Selma, Ala 
 
 I5>400 
 
 1900-1908 
 
 24.01 
 
 
 
 
 
 
 7.300 
 
 1899-1908 
 
 
 
 
 
 
 Rock Hill, S. C 
 
 2,990 
 
 189S-1903 
 
 25.21 
 
 
 
 Tar 
 
 Tarboro, N. C 
 
 2.290 
 
 I 896-1900 
 
 
 
 
 Roanoke 
 
 Randolph, Va 
 
 3.080 
 
 1901-190S 
 
 18.86 
 
 
 Pt. of Rocks. Va 
 
 9.650 
 
 1895-1906 
 
 
 
 
 
 Oswego, N. Y 
 
 5,000 
 
 1897-1901 
 
 
 
 
 Delaware 
 
 Port Jarvis, N. Y 
 
 3.250 
 
 1904- I 908 
 
 22.20 
 
 Susquehanna 
 
 Binghamton, N. Y 
 
 2,400 
 
 1901-1906 
 
 28.88 
 
 
 Mechanicsville, N. Y. . . 
 
 4.500 
 
 1891-1900 
 
 22-95 
 
 
 
 Dunsbach Ferry. N. Y.. 
 
 3,440 
 
 1898-1907 
 
 23.28 
 
 
26 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 Comparison of Runoff. — A comparison of the runofE on different 
 watersheds frequently leads to interestmg conclusions, especially 
 when the various- factors which influence it are considered. If a 
 comparison is made without first considering the amount and char- 
 acter of rainfall, the nature of the soil, and losses by evaporation, 
 the results are not only confusing but frequently lead to far-reaching 
 engineering blunders. For example, the earliest data available 
 were from watersheds in New England or New York. These were 
 fairly consistent among themselves and it was possible to deduce 
 rules for local application to the effect that about 30 per cent, of the 
 rainfall might be found in the stream. Engineers have some times 
 taken these conclusions and attempted to apply them in the west, 
 with the result that they have been greatly misled in their assump- 
 tions of available water supply. 
 
 This has been due not merely to the fact that direct comparison 
 could not be made, but also to what should have been even more 
 obvious; namely, that the measured rainfall in the west has been 
 mostly in the valleys and rarely on the higher portions of the catch- 
 ment area from which comes the greater part of the water. 
 
 It is important and necessary in some cases to make deductions', 
 based upon comparisons or runoff of various watersheds, since it 
 has not been possible to measure the runoff from every stream. 
 When such comparisons are made, however, great care must be 
 exercised in selecting areas which are similar in character. It is 
 recognized that an area of 1,000 square miles may have a different 
 character of runoff from one of 100 square miles, even in the same 
 region, so that when it is desirable to study the amount of water 
 probably available from a river basin of a thousand square miles, 
 it is important to obtain the measurements which have applied to a 
 similar area and not to one notably larger or smaller. 
 
 It must be recognized that conclusions drawn from such compari- 
 sons are at best subject to grave error, and that an accurate value 
 of runoff can be had only by direct measurement. 
 
 Measurement of Water. — The measurement of water may prop- 
 erly be considered under two heads, namely, measurement of supply 
 and measurement of duty requirement. 
 
 Measurement of supply is for the purpose of determining the 
 quantity of water available for irrigation, power development and 
 domestic use. It includes the measurement of runoff from the vari- 
 ous streams and to a limited degree also the determination of under- 
 ground flow which may be made available for use through pumping 
 
Pt.atk TI 
 
 i-"i(;. A.---M(;UitH| <)i rnakini;; u measurenu-nt oi' I k<- anioini: 
 
 rf Ml a -^Ucain. 
 
 
 Fig. B. Making similar measurements by wading. 
 
 (Facing Page 26) 
 
Plate IT 
 
 ^ 
 
 / J 
 
 -asKia x^mj^]mm '8','«,;gai,SiA?*' 'ff '^ '^ 'f^SJMU 
 
 ^^ 
 
 Fig. C. — Meters used for measuring the velocity of the flowing water. 
 
WATER SUPPLY 27 
 
 or artesian flow. Measurement of duty requirement includes the 
 determination of the amount used for irrigation, power development 
 and other purposes. 
 
 Both of the above classes of measurements are necessary in an 
 enterprise involving the use of 'water; the first to determine the 
 amount available and the second to determine the extent of an enter- 
 prise which a given supply will furnish. 
 
 The methods of measuring water in natural streams in a systematic 
 and economical manner have been developed within the last twenty 
 years, largely by the efforts of the United States Geological Survey. 
 Notable progress has been made in simphf)dng details and in adapt- 
 ing them to methodically carrying on work over a wide extent of 
 country. There has been a gradual evolution of the instruments 
 employed, especially along the Une of lightness and portability. 
 
 Briefly stated, the work consists of measuring and recording the 
 total quantity of water which passes a given point in a stream and 
 in this manner determining the runoff from each of the principal 
 watersheds. It has not been possible, up to the present time, to 
 measure all of the streams of the country; enough, however, are 
 being measured to permit rough estimates of the total supply being 
 made and the work is being gradually extended with the increasing 
 demand for water-supply data. Measurements of the quantity of 
 water used in various enterprises are also being carried on, both by 
 the United States and public utility corporations. 
 
 Units of Measurement. — Two classes of units are commonly used 
 in the measurement of water, the first representing quantity and the 
 second rate of flow. 
 
 Quantity is measured in terms of some well-defined unit of capac- 
 ity and is used to express the amount of water contained in a reservoir 
 or that applied to a given area of land in the process of irrigation. 
 The units of quantity commonly used are the gallon, the cubic foot 
 and the acre-foot. The gallon and cubic foot are employed in ex- 
 pressing the quantity of water stored or used for domestic purposes, 
 but, on account of the smallness of each of these units, they are sel- 
 dom used in engineering estimates of irrigation work. Instead the 
 acre-foot is the common unit. It is defined as the amount of water 
 required to cover i acre i ft. deep or 43,560 cu. ft. Capacities of 
 large reservoirs are generally given in acre-feet, these figures being 
 thus immediately computable with the agricultural areas. 
 
 Rate of flow may be defined as the quantity of water flowing 
 through a pipe or channel in a given unit of time, usually the second. 
 
28 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 The units are the miner's inch and second-foot. The miner's inch, 
 the first unit expressing rate of flow generally employed in the 
 United States, is supposed to represent the quantity of water which 
 flows continuously through an orifice i in. square under a given head. 
 The head on the orifice has been variously defined in different local- 
 ities but is ordinarily taken as about 4 in. above the top of the orifice. 
 The second-foot is defined as i cu. ft. per second of time. A box 
 or conduit i ft. square carrying water with a velocity of i ft. per 
 second would deliver i second-foot. The second-foot, on account 
 of its definiteness, is the most desirable unit for expressing rate of 
 flow and the one commonly used by American and English engineers. 
 By the latter it is written "cusec." 
 
 
 Fig. 8.— Method of measuring miner's inches. 
 
 The miner's inch is indefinite since the quantity of water which 
 wUl flow through an orifice i in. square under a fixed head depends 
 upon the thickness of the medium in which the orifice is made. For 
 example, the amount of flow through an orifice cut in a plank 2 in. 
 in thickness will be very different from that through the same size 
 orifice cut in a thin sheet of metal. 
 
 One of the methods of measuring miner's inches is indicated by 
 the accompanying illustration. Fig. 8, in which a rectangular orifice 
 is so arranged as to be capable of adjustment to various widths by 
 
WATER SUPPLY 29 
 
 means of a slide, rendering it practicable to measure quantities from 
 one miner's inch up to 75 inches. This is fairly satisfactory for 
 these smaller quantities, but to measure" 10,000 miner's inches by 
 such device is practically impossible because of the fact that the 
 orifice must be of great horizontal extent to avoid the complications 
 of increased head if the orifice is enlarged in a vertical direction. 
 
 In order to avoid confusion growing out of the use of this unit, 
 most of the states have defined the miner's inch in terms of the second- 
 foot. In this, however, there is not an agreement among the various 
 States. In Idaho, Kansas, Nebraska, New Mexico, North and South 
 Dakota, 50 miner's inches equal i second-foot. In Arizona, Califor- 
 nia, Montana and Oregon, 40 miner's inches equal i second-foot. 
 
 On account of its indefiniteness and the fact that the miner's inch 
 is not well adapted to expressing the results of computations on the 
 rate of flow through flumes, over wiers and other measuring devices, 
 the use of the term should be discontinued. 
 
 "Second-feet per square mile" is the average number of cubic feet 
 of water flowing per second from each square mile of area drained, 
 on the assumption that the runofi is distributed uniformly both as 
 regards time and area. 
 
 "Runofi in inches" is the depth to which the drainage area would 
 be covered if all the water flowing from it in a given period were 
 conserved and uniformly distributed on the surface. It is used for 
 comparing runoff with rainfall, which is usually expressed in depth in 
 inches. 
 
 Convenient Equivalents. — The following is a list of convenient 
 equivalents for use in hydraulic computations: 
 
 I second-foot equals 7.48 United States gallons per second; equals 448.8 gallons 
 per minute; equals 646,272 gallons for one day. 
 
 I second-foot equals 6.23 British imperial gallons per second. 
 
 I second-foot for one year covers i square mile 1.131 feet or 13.572 inches deep. 
 
 I second-foot tor one year equals 31,536,000 cubic feet. 
 
 I second-foot equals about i acre-inch per hour. 
 
 I second-foot for one day covers i square mile 0.03719 inch deep. 
 
 I second-foot for one 30-day month covers i square mile 1.116 inches deep. 
 
 I second-foot for one day equals 1.983 acre-feet. 
 
 I second-foot for one 30-day month equals 59.50 acre-feet. 
 
 100 United States gallons per minute equals 0.223 second-foot. 
 
 100 United States gallons per minute for one day equals 0.442 acre-foot. 
 
 1,000,000 United States gallons per day equals 1.55 second-feet. 
 
 1,000,000 United States gallons equals 3.07 acre-feet. 
 
 1,000,000 cubic feet equals 22.95 acre-feet. 
 
 I acre-foot equals 325,850 gallons. 
 
30 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 I inch deep on i square mile equals 2,323,200 cubic feet. 
 
 I inch deep on i square mile equals 0.0737 second-foot per year. 
 
 I foot equals 0.3048 meter. 
 
 I mile equals 1.60935 kilometers. 
 
 I acre equals 0.4047 hectare. 
 
 I acre equals 43,560 square feet. 
 
 I acre equals 209 feet square, nearly. 
 
 I square mile equals 2.59 square kilometers. 
 
 I cubic foot equals 0.0283 cubic meter. 
 
 I cubic foot equals 7.48 gallons. 
 
 I cubic foot of water weighs 62.5 pounds. 
 
 I cubic meter per minute equals 0.5886 second-foot. 
 
 I horse-power equals 550 foot-pounds per second. 
 
 I horse-power equals 76 kilogram-meters per second. 
 
 I horse-power equals 746 watts. 
 
 I horse-power equals i second-foot falling 8.80 feet. 
 
 I 1/3 horse-power equals about i kilowatt. 
 
 ^ , , .,, Sec.-ft.XfaU in feet 
 
 To calculate water-power quickly: = net horse-power on 
 
 water wheel realizing 80 per cent, of theoretical power. 
 
 Methods of Meastirement. — The measurement of water is in 
 practically all cases accomplished by taking the rate and time of flow 
 and computing the amount of discharge from these factors. Where 
 the rate of flow is constant the quantity is the rate multiplied by the 
 time. Where the rate of flow varies from day to day or, as is often 
 the case, from hour to hour, an account must be taken of these varia- 
 tions. This is done by computing the amount of discharge for 
 ■ short periods of time, for example, a day or an hour, and summing up 
 these amounts over the entire period of flow. In the work of the 
 United States Geological Survey the amount of discharge for each 
 day is used as a basis for determining the mean monthly or yearly 
 discharge. 
 
 The measurement of rate of flow or stream measurement as it is 
 usually called is based primarily upon measurements of the cross- 
 sectional area and mean velocity through the measured section. In 
 some cases, more especially on small streams or in irrigation or supply 
 canals, measurements are made by special devices, such, for example, 
 as wiers. 
 
 The accompanying illustration, Fig. 9, gives the ideal arrange- 
 ment of a fully equipped gaging station. In the foreground is a 
 small structure enclosing a self-registering device for keeping record 
 of the rise and fall of the water in a small well connected with the 
 river by a horizontal pipe, near it is a vertical gage rod to check the 
 observations by direct reading. Devices of this kind are somewhat 
 
WATER SUPPLY 
 
 31 
 
 expensive to install and require frequent skilled attendance to adjust. 
 In the background is a cable suspended across the river from which 
 is hung a seat or small car from which the hydrographer can 
 work while measuring the width, depth, and velocity of various 
 portions of the stream. (See also Plate II, Figs. A and B, illus- 
 trating measurements from a small bridge or made by wading the 
 stream.) 
 
 The cross-sectional area of a stream is measured by taking sound- 
 ings at regular intervals, of say 5 or 10 ft., across the stream and 
 computing the areas of each of the small sections between soundings 
 
 Fig. 9. — Equipment for river station, consisting of self-registering height 
 gage, protected by small house with cable and car for convenience in velocity 
 measurements. 
 
 from its width and mean depth. The sum of the small areas thus 
 obtained is the total cross-sectional area. The velocity is determined 
 either by means of a current meter, Plate II, Fig. C, placed in the 
 stream, or by means of floats on the surface. The former method is 
 susceptible of the greater accuracy and is the one generally used in 
 stream-gaging work. In computing the discharge, account must be 
 taken of the fact that the velocity varies in different parts of the 
 stream and that it is necessary to divide the total cross-section 
 into parts and compute the discharge through each part separately. 
 This can be done readily when velocity measurements are made by 
 means of the current meter at various points in the stream. When 
 velocity is measured by means of floats it is generally assumed that 
 
32 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 the mean velocity is about 0.8 of the surface velocity. Measure- 
 ments by this method are at best but rough estimates and for this 
 reason should not be relied upon where reasonably accurate results 
 are required. 
 
 Where conditions will permit of its installation and use, the wier 
 is probably the most accurate method of measuring water. The 
 conditions necessary for accurate wier measurements are such, 
 however, that they frequently cannot be secured on streams of any 
 considerable size. Accurate wier measurements require first, that 
 the water above the wier be in a quiescent state and that the fall 
 be sufficient that the surface of the water in the stream on the lower 
 side of the wier be below the top of the wier crest. It is readily 
 seen that these conditions are diflScult to obtain on streams of any 
 considerable size. 
 
 Results of Stream Measurement. — The results of stream measure- 
 ment indicate a wide fluctuation in the quantity of flow from month 
 to month, and from year to year. As a rule the minimum flow is 
 when water is most needed for irrigation or during the months of 
 July and August. It increases gradually as cooler weather comes 
 on, continuing, however, at a relatively small amount during the 
 winter, and reaching the flood stage during the spring months. 
 The maximum flood follows the spring rains and melting snow occur- 
 ring generally in the latter part of May or in June. 
 
 Besides the annual variations of drought and flood, there is what 
 is sometimes called the "non-periodic" alternation of wet and dry 
 years. For several years in succession, the floods will be high and 
 prolonged, and the low-water season will yield a fair amount of 
 water for irrigation, then follows one or two or sometimes three 
 years in succession of unusual drought, when the floods are very 
 small and the runoff not sufficient to fill the reservoirs which may 
 have been provided. In planning irrigation works, full considera- 
 tion must be given to the fact that these years of drought frequently 
 occur in succession. 
 
 Attempts have been made to discover some rule governing the 
 occurrence of wet and dry years. One has worked out a theory 
 that droughts occur at intervals of seven years, while another is 
 equally certain that an eleven-year period is more nearly correct, 
 and still again there are advocates of a seventeen-year period. For 
 practical purposes, there is no rule which can be depended upon 
 other than that whatever has happened in the way of extreme 
 drought or flood is likely to happen again, and that a series of wet 
 
WATER SUPPLY 33 
 
 years is likely to be followed by dry years, the length of duration of 
 each of these periods being unknown. 
 
 The actual quantities of water in the principal streams month 
 by month and year by year is given in the publications of the United 
 States Geological Survey, these quantities being stated both in 
 average rate of flow or cubic feet per second, and in total quantity 
 delivered during the period in acre-feet. 
 
 Quality of Water Supply. — In addition to its quantity, the quality 
 of a water supply to be used for irrigation should be examined. 
 Water in its flow dissolves and carries out of the soil or rock over 
 which it travels small quantities of mineral or alkali salts. As a 
 result of this gradual accumulation, no stream waters are absolutely 
 pure. Some of these salts are harmless, while others are highly 
 injurious to plant growth. 
 
 In the arid west where the rainfall is Umited, and where, as is 
 frequently the case, the character of the rock is such that disintegra- 
 tion proceeds rapidly, the quantity of salts in solution is far greater 
 than in the more humid regions of the east. Where the rocks are 
 mostly crystalline, such as the granites, the stream waters are more 
 nearly free from matter in solution, but where the flow is over shales, 
 they frequently become highly charged. If waters used for irriga- 
 tion contain any considerable quantity of salts in solution, there is 
 danger of the soil becoming sufiiciently impregnated to render it 
 unfit for growing crops. This is especially the case if the soils 
 themselves previous to irrigation contain a small amount of these 
 harmful soluble salts. 
 
 There is no hard and fast rule as to the amount of soluble salts 
 or alkali required to render water unsafe for irrigation purposes. 
 This will depend upon the character of the salts, the natural con- 
 ditions of the soil, the amount of water used in irrigation and the 
 efficiency of underground drainage to prevent alkali accumulation 
 on the surface. Few of the natural stream waters are unfit for irri- 
 gation purposes if proper precautions are taken in their use, and the 
 lands to which they are applied are not already strongly charged 
 with alkali. It is important to know the quality of waters, not for 
 the purpose of condemning them but to insure their proper use. 
 
 It is frequently stated that one-tenth of i per cent, of soluble 
 salts, or loo parts of salts in 100,000 of water, is the limit of safety 
 in irrigation waters. There are, however, instances where water 
 containing two or three times this amount have been used without 
 notable injury. On the other hand, waters containing less than half 
 
34 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 this amount when carelessly used have been known to injure large 
 areas. In passing upon the quality of irrigation waters the character 
 of the soluble salts they contain and the conditions under which they 
 are to be used must be considered. 
 
 Amount of Water Required for Irrigation. — ^The amount of water 
 which is required for successful production of crops is dependent 
 upon the climate, soil, and kind and number of crops grown. As 
 a rule, where water is plentiful, too much is applied to the land, 
 especially by unskilled irrigators. The most skillful irrigator ob- 
 tains the best results with the smallest amount of water. Thorough 
 cultivation rather than excess use of water is the secret of success 
 and the man who attempts to save labor in cultivating by putting 
 on additional water will usually reduce the crop production and en- 
 danger his own and possibly also his neighbor's land. 
 
 Roughly stated, the amount of water required for successful 
 irrigation varies from i to 3 acre-feet per acre per annum, or an 
 amount sufficient to cover the land from i to 3 ft. in depth. In 
 some sections of extreme aridity, where climatic conditions are such 
 that crops grow during practically the entire year, this latter 
 amount may be exceeded. 
 
 Heavy soils through which water percolates but slowly require, 
 as a rule, less water than the more porous soils. These soils, how- 
 ever, require thorough cultivation to keep them in proper condition 
 to absorb and hold the water which is applied to them. Under 
 drought conditions, excellent crops have been raised and orchards 
 caused to produce heavily with water carefully applied at the rate 
 of only I or I 1/2 acre-feet per acre per annum. 
 
CHAPTER IV 
 DESIGN AND CONSTRUCTION OF CANALS 
 
 Capacity. — ^The capacity of a canal at any given point is the 
 amount of water which will pass that point under normal conditions. 
 In preparing plans for construction or enlargement it is necessary to 
 know the agricultural area which the canal is to serve and the duty 
 of water for which provisions must be made during the period of 
 greatest irrigation requirement. In considering the total annual de- 
 mand for water it is advisable to divide the requirements into months 
 or shorter periods covering the entire irrigation season. Where data 
 are not at hand to determine the actual amount of water required 
 for maximum irrigation during any one month, various assumptions 
 must be made and these estimates shovild be suflSciently liberal to 
 provide for all future emergencies. If, for example, it is known that 
 during an irrigation season of say six months in length, 30 in. 
 in depth or 2 1/2 acre-feet per acre is required, it is probably safe 
 to assume at least 40 per cent, in excess of this average amount, 
 or a depth of 7 1/2 inches, may be required in a single month during 
 the period of greatest irrigation. 
 
 Having arrived at the amount of water needed in the month of 
 maximum demand the capacity of canal is found by multiplying the 
 depth in feet of water required by the total number of acres to be 
 supplied and dividing by the number of days in the month. This 
 will give the number of acre-feet required daily, which may be re- 
 duced to second-feet by again dividing by 1.98, since i second- 
 foot continuous flow for twenty-four hours equals 1.98 acre-feet. 
 
 The above is satisfactory for the design of main canals or large 
 laterals where a practically continuous flow can be maintained 
 from day to day. In the design of smaller canals or laterals, in- 
 tended to serve but a small area, account must be taken of the fact 
 that such canals may not be in continuous use. Provision must 
 be made for delivering the required amount of water during the 
 period of time that irrigation will probably be carried on from such 
 canal. For example, a canal with a carrying capacity of 10 cu. ft. 
 per second will deliver approximately 20 acre-feet per day, or 600 
 acre-feet per month. Such a canal with a maximum duty of water 
 
 35 
 
36 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of 1/2 acre-foot per month is capable, theoretically, of irrigating 
 1,200 acres. It is probable, however, that the irrigation of a tract 
 of this size for economic results will not require continuous irrigation, 
 but that irrigation may be carried over the entire area in a period 
 of from ten to fifteen days and no further application of water might 
 be required for an equal period of time. 
 
 In fixing the capacity of a canal it is necessary to take account of 
 the actual time that the canal is to be in operation and to provide 
 for delivering the amount of water required during this period. 
 Account must also be taken of probable losses by seepage and 
 evaporation. The amount of these will depend upon the length 
 of the canal, the nature of material, and climatic conditions. No 
 definite rules can be laid down for their determination. Where 
 data are at hand relative to seepage and evaporation losses these 
 can be determined. Where such data are not at hand, estimates 
 for them must be made. The capacity of a canal should be suf- 
 ficient to provide for the net quantity of water required on the 
 land in addition to the evaporation and seepage losses which are 
 expected. 
 
 A convenient method of determining the capacity of a canal 
 required for a given area is to first find the area which will be served 
 by a continuous flow of i cu. ft. of water per second, which may 
 be computed as foUows: 
 
 Let a = area 
 
 d = maximum duty of water, that is, the depth required on the 
 
 land for a given period of time 
 t = number of days in the period considered 
 p = percentage of loss by seepage and evaporation from the 
 canal 
 Then 
 
 43,560 ai = 86,40o t{i.oo-p) 
 or 
 
 _86,4ooi(i.oo-p)_i.98 t{i.oo—p) 
 ~ 43>S6o d ~ d 
 
 If we assume the duty of water for a period of thirty days to be 
 0.6 ft. on the land and the loss by seepage and evaporation in the 
 canal to be 10 per cent, of the total flow, 
 
 1.98X30X0.90 
 
 a= "S ^—=79.1 acres 
 
 0.6 " 
 
 Location of Canals. — Under the term "location" of a canal is 
 
DESIGN AND CONSTRUCTION OF CANALS 37 
 
 included its relation to the source of supply, the points of delivery 
 and all other natural or cultural conditions. In locating canals 
 there are to be considered, among other items, (a) economy of con- 
 struction and maintenance; (b) safety against possible breaks; (c) 
 the maximum amount of land that can be irrigated under the system. 
 Preliminary surveys, sufficient to determine a close approximation to 
 the area to be watered must first be made. With this data and an 
 assumed duty of water, the capacity of the canal can be determined. 
 The next step is to design a typical section of canal and fix its slope. 
 The various questions to be considered in this design are treated in a 
 later paragraph, so that for the present it is sufficient to assume as 
 fixed the cross-section of the canal and banks and the grade upon 
 which the location is to be made. 
 
 For economic construction a canal should be so located that the 
 excavations wiU equal the embankments, with a reasonable allow- 
 ance, say about lo per cent, for shrinkage. The depth of cut neces- 
 sary for this is defined as the normal or economic cut. Before 
 starting the actual work of location in the field the economic cut for 
 level ground and side slopes of various degrees should be computed, 
 for the ready reference of the engineer in charge of the location. 
 Data of this kind are valuable for use in the field in determining the 
 location for minimum cutting, which is one of the important factors 
 in location. 
 
 Besides the minimum amount of excavation it is necessary to 
 consider other factors. On sloping ground it is often necessary 
 to excavate more material than is required for banks in order to put 
 the waterway sufficiently in cut to insure safety. In locating along 
 a slope broken by long narrow ridges it is frequently a matter of econ- 
 omy and good engineering on account of savings in length and in the 
 elevation of water surface, to cut through the ridges rather than 
 attempt to go around them on approximately the contour of the canal. 
 The same remarks apply equally to the crossing of long and narrow 
 depressions or draws, where the amount of material excavated is not 
 sufficient and material has to be hauled from the adjacent ridges or 
 taken from borrow pits to f orin the banks. It is frequently advisable 
 to locate two or more alternate lines and make preliminary estimates 
 of cost before the final location is determined. 
 
 Where fills are contemplated careful attention should be given the 
 location on account of the great danger of breaks and of increased 
 cost of maintenance. In locating the larger main canals especially, 
 the question of safety should be given first consideration. It must be 
 
38 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 remembered that the extra cost of maintenance of a canal on a 
 treacherous location, while an important factor, is of less importance 
 than the possible losses of crops by the failure of the canal during 
 that period of an irrigation season when water is most needed. This 
 is notably true in extreme arid regions where the application of water 
 is an absolute necessity for agricultural operations. 
 
 Alignment. — ^The accurate alignment of a canal is of secondary 
 importance to economic and safe location. The ehmination of 
 sharp turns and reduction of curvature is desirable in order to reduce 
 the length and to guard against erosion, which sometimes occurs on 
 short curves. The requirements of alignment presented in the loca- 
 tion of a canal are less rigid than in railroad work. There are, how^ 
 ever, certain matters which should be given consideration. At the 
 end of long tangents, where wave action may prove considerable, as is 
 the case in large canals, the curves should be made as gentle as 
 possible in order to avoid washing of banks. Especial precautions 
 should be taken if the exposed bank is in fill. Shorter curves may 
 be used with the same degree of safety if the curve is thrown into the 
 slope, as is the case when passing around the head of a draw, than 
 when the curve is thrown outward as in passing around the point of a 
 ridge. This is on account of the greater velocity and increased 
 tendency to erosion on the outside of the carves. 
 
 The precise amount of resistance which a curve offers to the flow 
 of water in open channels has not been definitely determined. It is 
 believed, however, for velocities of flow which are safe for earthen 
 canals that a curve in the center line whose radius is two and one- 
 half times the bottom width of the canal may be used without any 
 appreciable effect on the average rate of flow. The above rule is 
 considered by some engtueers as a safe one to apply in determining 
 the alignment of canals. There are, however, numerous examples 
 where this curvature is exceeded and satisfactory results obtained, 
 especially where a canal is principally in cut, so that erosion does not 
 have the effect of weakening the banks. 
 
 Cross-section. — The selection of a cross-section for a canal is one 
 involving economy of construction and maintenance as well as se- 
 curity against failures which may prove disastrous to an irrigation 
 system. It requires the consideration of the theory of flow of water 
 in channels and the exercise of engineering judgment. From the 
 standpoint of theory alone it would appear the section which will (a) 
 carry the necessary amount of water; (b) conserve grade so as to 
 cover the greatest possible area and, (c) require the least amount 
 
DESIGN AND CONSTRUCTION OF CANALS 39 
 
 of excavation in its construction, is the one which should be selected. 
 For a canal of given slope and fixed area of cross-section the greatest 
 velocity will be attained by selecting the section with the maximum 
 hydraulic radius. From this it follows that such a section will re- 
 quire less grade for the same capacity than any other of equal area. 
 It can be shown that a circular or semi-circular section has the largest 
 hydraulic radius for a given area. It can also be shown for rectangular 
 and trapezoidal sections that when the width of surface is equal to 
 the sum of the two side slopes and the hydraulic radius is equal to 
 one-half of the depth of water the hydraulic radius is a maximum. 
 The most advantageous rectangular section is one whose top width 
 is equal to twice the depth. For trapezoidal sections certain fixed 
 relations between width and depth of water, depending upon the 
 steepness of side slopes, must be maintained in order to get a maxi- 
 mum hydraulic radius. These relations, for a few of the more com- 
 mon slopes in use, are as follows: 
 
 Slopes 1/2 hor. to 1 ver. — surface width = 2.24Xdepth. 
 Slopes I hor. to i ver. — surface widtli=2.83Xdepth. 
 Slopes 1 1/2 hor. to i ver. — surface width = 3.6oXdepth. 
 Slopes 2 hor. to i ver. — surface width = 4.47 X depth. 
 
 These sections, while theoretically the most advantageous, 
 are generally not the most practical, on account of the excessive 
 depths required for canals of large cross-sectional areas. The 
 accompanying illustration indicates sections on which canals have 
 been built under ordinary conditions of nearly level or slightly 
 sloping ground. 
 
 In buUding earthen canals it is necessary, for the sake of economy, 
 to utilize the embankments to form a part of the waterway. In 
 other words, the water must be held in part against the bank in 
 order to reduce seepage and minimize the danger of breaks. It 
 is advisable also to limit the pressure or head against artificial 
 banks. Generally a wide and shallow canal is less liable to cause 
 trouble due to seepage than a narrow and deep one. The shallow 
 canal, on the other hand, for the same area of cross-section, requires 
 more grade to give it the same carrying capacity than a narrow 
 and deep canal. The relative advantages of various tjrpes of 
 section has been the subject of considerable discussion among 
 irrigation engineers. The arguments presented, while of value 
 in considering an individual case, do not lead to general conclusions. 
 The narrow and deep section, while gener3,lly requiring a less amount 
 
40 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of excavation for a given capacity and grade, may prove the more 
 expensive of construction on account of the character of excavation 
 encountered, and difl&culty of removing materials from a greater 
 depth. A wide and shallow canal on side hills has the disadvantage 
 of requiring large amounts of excavation on the upper side, and 
 does not permit of keeping the waterway well within the excavated 
 portion of the channel on the lower side without considerable cost. 
 No fixed rules for the selection of a canal section can be formu- 
 lated, but each particular case must be treated with due regard 
 
 ^go- 
 Typical Canal Sections 
 
 Fig. io. — Typical cross-section of irrigation canals in level or sloping ground 
 and in relatively firm material. 
 
 to safety and economy of construction. In practice it is necessary 
 to consider the maximum depth of water a canal can safely carry, 
 the height of water surface above the natural ground surface, and 
 the depth to which excavations can be made economically. In 
 large canals these factors will ordinarily control in fixing the depth 
 of section and the area required for necessary capacity will determine 
 the width. For small canals, where the depth is not great and where 
 grade is sometimes an important factor, consideration should be 
 given to the section of greatest hydraulic radius. 
 
 Canals on comparatively level ground are sometimes constructed 
 
DESIGN AND CONSTRUCTION OF CANALS 41 
 
 by placing the embankment back a few feet from the upper slope 
 of the excavation, thus forming a berm. The effect of this is to 
 increase the cross-sectional area without increasing the amount 
 of excavation. On account of the comparatively shallow water near 
 the embankments, the velocities in this portion of the section are 
 reduced and there is less tendency to erosion of the banks. The 
 section of a canal constructed with a berm, except over very flat 
 country, is irregular in area, the water being restricted to a narrow 
 channel where cuts are deep and allowed to widen out where the 
 cutting is shallow. Where it is necessary to operate canals at 
 varying capacities the berms are alternately wet and dry, and 
 conditions are favorable for a growth of weeds and grass. It is 
 believed that in general, berms are a disadvantage rather than an 
 advantage and that the most satisfactory results are attained by the 
 use of a uniform cross-section with side slopes suflaciently flat to 
 prevent erosion and a gradual sloughing into the canal. 
 
 Slopes and Width of Banks. — The degree of steepness of the 
 slopes to which canal banks should be constructed depends largely 
 upon the character of materials. As has been shown in the previous 
 paragraph, the steeper the inner side of the banks, the less the 
 amount of excavation required in order to form a channel of given 
 capacity. This is more marked in deep cuts, where a large part of 
 the excavation is above the water section. It follows then for 
 deep cuts that the slopes of banks should be made as steep as the 
 material will stand with safety. This varies from about 1/2 hori- 
 zontal to I vertical for rock to about 3 horizontal to i vertical for 
 ordinary Ught earth. In some cases slopes may be made steeper 
 than 1/2 to i; in general, however, slopes steeper than this ex- 
 cept in very firm rock have a tendency to slough, due to weather- 
 ing, which results in a gradual filling of the channel. 
 
 For earthen slopes, material is seldom encountered that will 
 stand on a greater slope than i 1/2 to i. In that portion of the 
 channel forming the waterway, there is a tendency for the sides 
 to be gradually eroded or eaten away by the action of the water. 
 The greatest erosion usually takes place a short distance below the 
 surface of the water and from this point the cutting gradually 
 decreases toward the bottom. The effect of this erosion is to form 
 a rounded channel in which the sharp angle of intersection between 
 sides and bottom is eliminated. The general result is a flattening 
 of the sides of the entire bank, due to erosion and the weathering 
 of the material above where the erosion takes place. Banks con- 
 
42 PRINCIPLES OF IRRIGATION ENGINEERING 
 
DESIGN AND CONSTRUCTION OF CANALS 43 
 
 structed with i 1/2 to i slopes after a few years are found to have 
 become 2 to i or even flatter. When it is desired to maintain a 
 roadway on the top of an embankment it is necessary to construct 
 it somewhat wider than will be eventually required on accoimt 
 of the reduction in width which follows the flattening of the slopes. 
 Where the embankments are constructed with flat slopes the tend- 
 ency for the top width to decrease is lessened. On the outer slopes 
 of banks there is a less tendency to flattening, partly due to absence 
 of water against them and the consequent effects of erosion and 
 softening of the material. In very light materials, however, wind 
 action may have an important effect in reducing the outer slope. 
 One of the dangers in too steep outer slopes, especially in new canals, 
 is the tendency to slough or run when the bank becomes saturated. 
 This danger may become serious in banks of considerable height 
 built of light permeable material. The top width of banks required 
 and its height above the water surface in the canal are questions 
 to be decided in each particular case and will depend upon the 
 depth of water and character of the materials of which the banks 
 are constructed. For the larger and more important canals it 
 is believed that the height of banks above the maximum water 
 surface should not be less than 3 ft. and the top width not less than 
 8 or 10 ft. Where a roadway is maintained on the top of banks 
 this width should be increased. 
 
 Material for Banks. — Ordinarily there is but little choice of mate- 
 rials for forming the waterway for canals, since in most cases it is 
 necessary, to keep the cost within reasonable limits, to use for this 
 purpose the natural materials found on the canal location. It 
 frequently occurs that canals are required to be constructed through 
 soils or rocks which are exceedingly pervious to water, and the en- 
 gineer is called upon to decide whether or not a channel can be 
 constructed that will be reasonably water tight. This question 
 involves not only that part of the waterway formed above the 
 natural ground surface by means of artificial banks but applies to 
 that portion of the channel which is in cut also especially on side- 
 hill work. Clay is perhaps the least permeable of the various mate- 
 rials through which canals are buUt, while coarse sand or gravel 
 offer least resistance to the passage of water. The question of 
 permeability of earth depends upon the amount of fine material 
 which it contains. Sand or gravels are composed of solid particles 
 of appreciable dimensions, voids of notable size occurring between the 
 particles. The same is also true in broken or shattered rock forma- 
 
44 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 tion, where the spaces between the rock are not filled with earth or 
 other fine material. Clay, on the other hand, composed of fine 
 particles, has correspondingly small voids, so small as not to permit 
 the ready passage of water. 
 
 In addition to the question of permeability, the character of the 
 materials should be taken into account in fixing the cross-section, 
 the slopes of banks and the velocities which can safely be maintained. 
 Where the quantity of material capable of making a water-tight bank 
 is limited, a segregation of materials is sometimes necessary, the 
 water-tight material being placed either on the inner face or in the 
 form of a core in the center of the bank. In general it is more 
 economic to place this material on the inner slope of the canal than 
 in the center of the bank. In this position, however, there is some 
 danger of the face of the slopes being carried away by erosion, or 
 by a breaking down into the canal, thus leaving the porous sub- 
 strata exposed. 
 
 The treatment of side slopes applies equally well to the bottom of 
 canals in porous materials. Soils and loams which contain a con- 
 siderable amount of vegetable matter usually form tight banks, but, 
 on account of the material being comparatively light, require 
 relatively flat slopes. Sufficient clay mixed with sand or gravel to 
 fill up the pores and give it solidity makes a good material for banks. 
 In constructing canals where different materials are encountered in 
 the excavations, it is good practice to specify that the coarse mate- 
 rials shall be placed in the outer and the finer materials in the inner 
 portion of the banks. 
 
 Grades and Velocities. — ^The grades of canals are fixed in many 
 cases by practical rather than by theoretical considerations. Where 
 the grade must be kept to the minimum in order to reach the largest 
 practicable area of irrigable land the relative elevations of the head of 
 a canal and the lands are the controlling factors. In this case, 
 velocity and some economy of construction of the canal is sacrificed 
 in order to increase the irrigable area. The problem which the 
 engineer is required to solve is to find the point of balance between the 
 extra cost of construction and the value of the additional lands 
 which may be irrigated. Where there is ample grade, so that the 
 holding up of a canal is unnecessary, the problem presented is one 
 of greatest economy of design and construction consistent with 
 safety and economy of operation. 
 
 There are certain limitations which cannot be overlooked. If 
 the grade of a canal is too fiat and the corresponding velocity of 
 
DESIGN AND CONSTRUCTION OF CANALS 45 
 
 flow too low there is a constant tendency to a filling up of the canal 
 due to deposits of silt from waters carrying material in suspension. 
 The growth of noxious weeds and grasses in a canal is also facilitated 
 by reducing the velocity beyond certain limits. Where grades are 
 too steep and velocities correspondingly high, erosion of the channel 
 is the result. 
 
 The ideal grade for a canal is one which will neither cause erosion 
 nor permit silt to be deposited. This condition, however, cannot 
 be fully realized, on account of the different materials through 
 which canals must be constructed and the varying character of the 
 materials carried in suspension. In order to prevent erosion in 
 canals it has been considered necessary that the velocities be kept 
 below certain limits for different classes of materials. These 
 limits are ordinarily stated to be from about 2 1/2 ft. per second for 
 very light soils to from S to 7 ft. per second for the firmest earth 
 materials. It is generally considered that erosion is a function of 
 the velocity and that account need not be taken of the grades 
 necessary to produce this velocity in canals of different sizes and 
 shapes of section. A further consideration of the subject seems to 
 show that erosion in a canal is a function of the grade, size and 
 shape of the section, as well as the velocity, or, in other words, it 
 is dependent, to a certain extent, upon the amount of energy ex- 
 pended by the current in overcoming the resistance of friction in the 
 channel. 
 
 This point may be illustrated by considering two canals of similar 
 -cross-sections, but of such relative sizes that the smaller requires 
 twice the grade as the larger to produce the same velocity of flow. 
 It is evident that the energy expended per unit quantity of water in 
 overcoming friction will be larger and consequently the tendency to 
 erosion greater in the smaller or canal of steeper grade. The same 
 principle applies to canals of equal cross-sectional areas but of such 
 different shapes of cross-sections that more grade is required in one 
 than the other to maintain the same velocity. The question as to 
 how much erosion in canals is affected by increased grades, velocities 
 remaining constant, is one upon which experimental data are lack- 
 ing. Observations on large and small canals constructed in the 
 same character of materials seem to indicate that the small canals 
 erode under lower velocities than larger canals. Take, for example, 
 a canal 4 ft. wide on the bottom with i 1/2 to i side slopes and 
 carrying water 3 ft. deep. The hydraulic mean radius for this 
 canal is approximately 1.7; with a grade of 0.00125, or 6.6 ft. per 
 
46 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 mile and a value of n= 0.025 the velocity of flow is approximately 
 2.90 ft. per second. Erosion under these conditions would probably 
 take place, except in the firmest materials. A canal 40 ft. wide on 
 the bottom with i 1/2 to i side slopes and canying water 10 ft. 
 deep would have a hydraulic mean radius of 7.6 and with »=o.o25 
 would require a grade of 0.00015, '^^ °-^ ft. per mile to give it the 
 same mean velocity. The latter grades and velocity would not be 
 considered excessive, and erosion would probably not occur in 
 average firm soil. 
 
 Silting of channels is a subject to which comparatively little atten- 
 tion has been given in the United States on account of the relatively 
 small amount of silt usually carried by irrigation canals. In India 
 and 'Egypt, where large quantities of silt are taken into canals, 
 considerable attention has been given to velocities and forms of 
 cross-sections to prevent deposit of this material. The velocity 
 required to prevent such deposit is dependent upon the character 
 and fineness of the material carried. It has been the common theory 
 that a velocity of 2 ft. per second was suflB.cient to prevent the deposit 
 of silt. It is probable, however, that a careful series of observations 
 under different conditions would show that in some cases silt would 
 be carried by lower and in other cases deposited by higher 
 velocities. 
 
 Mr. R. G. Kennedy, who has made extended studies and observa- 
 tions on silting of canals in India, advances the theory that the silt- 
 carrying power of a canal is a function of the depth of water as well 
 as of the velocity. From his experiments Mr. Kennedy has worked 
 out an empirical formula showing the relation between limiting 
 velocity at which silt will be deposited and depth of water, as follows: 
 V = Cd'" in which F = velocity at which silt begins to deposit, d the 
 depth of water and c and m constants. The values of these con- 
 stants as determined are £=0.84 and w=o.64. This theory shows 
 that silt will be carried by a less velocity in shallow than in deep 
 canals. 
 
 It has been found in practice that the varying of the cross-section 
 and grade of a canal each have a tendency to produce erosion and 
 silt deposits, and that the best results are obtained by maintaining 
 a uniform section and slope. 
 
 The following is a table of hydraulic functions of some of the 
 principal canals constructed by the U. S. Reclamation Service. 
 The values given for "n" are those assumed in the design of the 
 canals. 
 
DESIGN AND CONSTRUCTION OF CANALS 
 
 47 
 
 SECTIONS AND SLOPES OF SOME OP THE PRINCIPAL CANALS OF THE U. S. 
 RECLAMATION SERVICE 
 
 Project 
 
 Name of canal 
 
 Size 
 
 
 
 Velo- 
 
 Capac- 
 
 
 
 
 Bot- 
 
 
 slopes 
 
 city 
 
 ity 
 
 tom 
 
 Depth 
 
 
 
 
 width 
 
 
 
 
 
 20 
 
 13 
 
 l4:l 
 
 2.96 
 
 1,520 
 
 12 
 
 13 
 
 I :i 
 
 3.70 
 
 1,202 
 
 13 
 
 6 
 
 2 :l 
 
 2. S3 
 
 380 
 
 4 
 
 3 
 
 2 :i 
 
 1.6s 
 
 50 
 
 6 
 
 3 
 
 2 :i 
 
 1.73 
 
 62 
 
 34 
 
 10 
 
 ii:i 
 
 2.86 
 
 1,407 
 
 24-5 
 
 10 
 
 2 :i 
 
 2.94 
 
 1,220 
 
 30 
 
 9.S 
 
 i:l 
 
 2.7S 
 
 908 
 
 22 
 
 8.S 
 
 li:l 
 
 2. SO 
 
 738 
 
 23. S 
 
 10 
 
 lj:l 
 
 .2 . 14 
 
 824 
 
 23 
 
 8 
 
 ii:i 
 
 1.89 
 
 529 
 
 IS.S 
 
 6 
 
 l}:l 
 
 2.12 
 
 312 
 
 14- S 
 
 7 
 
 1} 
 
 
 2.29 
 
 401 
 
 II 
 
 5 
 
 1} 
 
 
 2.60 
 
 240 
 
 8 ■ 
 
 3 
 
 li 
 
 
 2.62 
 
 98 
 
 S 
 
 3 
 
 li 
 
 
 2.00 
 
 S6 
 
 4 
 
 2 
 
 1} 
 
 
 1.52 
 
 21 
 
 30 
 
 10 
 
 2 
 
 
 2.S 
 
 1,248 
 
 40 
 
 8.3 
 
 2 
 
 
 2.S 
 
 1. 175 
 
 40 
 
 9 
 
 I 
 
 
 3.08 
 
 1.358 
 
 27 
 
 7 
 
 1} 
 
 
 2. SI 
 
 659 
 
 23 
 
 7 
 
 1} 
 
 
 2.45 
 
 S7S 
 
 20 
 
 S 
 
 I 
 
 
 2.47 
 
 307 
 
 l5 
 
 5 
 
 ij 
 
 
 2.36 
 
 278 
 
 SO 
 
 IS 
 
 I 
 
 
 3.00 
 
 2,926 
 
 40 
 
 10 
 
 I 
 
 
 3.27 
 
 1,635 
 
 36.6 
 
 10 
 
 1} 
 
 
 3.22 
 
 1,659 
 
 ■44 
 
 II 
 
 li 
 
 
 2.2s 
 
 1,500 
 
 16 
 
 6 
 
 15 
 
 
 1.74 
 
 261 
 
 130 
 
 5.S 
 
 2 
 
 
 2.19 
 
 300 
 
 II. 8 
 
 s.s 
 
 1} 
 
 
 2.18 
 
 300 
 
 27 
 
 8 
 
 ij 
 
 
 2.70 
 
 850 
 
 40 
 
 6.S 
 
 2 
 
 
 2.91 
 
 1,000 
 
 20 
 
 9.7 
 
 2 
 
 
 2.58 
 
 1,000 
 
 Slope 
 
 Truckee- Carson. 
 
 Truckee- Carson. 
 
 Truckee- Carson. 
 
 Truckee-Carson. 
 
 Truckee-Carson. 
 
 No. Platte 
 
 No. Platte 
 
 No. Platte 
 
 No. Platte 
 
 Lower Yellow- 
 stone. 
 
 Irfjwer Yellow- 
 stone. 
 
 Lower Yellow- 
 stone. 
 
 Huntley 
 
 Huntley 
 
 Huntley 
 
 Huntley 
 
 Huntley 
 
 Uncompahgre . . . 
 
 TJncompahgre . . . 
 
 Belle Fourche. . . 
 
 Belle Fourche. . . 
 
 Belle Fourche. . . 
 
 Belle Fourche.. , 
 
 Belle Fourche. . . 
 
 Belle Fourche. . . 
 
 Belle Fourche. . . 
 
 Belle Fourche. . . 
 
 Klamath 
 
 Klamath 
 
 Umatilla 
 
 Umatilla 
 
 St. Mary 
 
 Shoshone 
 
 Shoshone 
 
 Main Truckee . . 
 Main Truckee . . 
 Lateral Line AA 
 Lateral Line F. . 
 Lateral Line I . . 
 
 Interstate 
 
 Interstate 
 
 Interstate 2nd. . 
 Interstate 2nd. . 
 Main 
 
 Main 
 
 Main 
 
 Main 
 
 Main 
 
 Main 
 
 Main 
 
 Main 
 
 South 
 
 South 
 
 North 
 
 North 
 
 North 
 
 South 
 
 South 
 
 Waste Channel . 
 
 Inlet 
 
 Inlet 
 
 Main 
 
 E. Branch 
 
 Feed 
 
 Feed 
 
 Main 
 
 Garland 
 
 Garland 
 
 0.000154 
 
 0.0003 
 
 0.0002 
 
 0.00025 
 
 0.0002 
 
 0.00017 
 
 0.00017 
 
 0.00017 
 
 0.00017 
 
 O.OOOI 
 
 0.002 
 0.0002 
 
 . 0004 
 . 0008 
 o.oooss 
 0.00055 
 0.000135 
 
 .00015 
 
 . 0002 
 
 .0002 
 
 .0002 
 
 .0003 
 
 .0003 
 
 .0001 
 
 .0002 
 
 .0002 
 
 .000081 
 
 .000132 
 
 .000201 
 0.000193 
 
 .0002 
 0.00022 
 0.00016 
 
 0.025 
 
 0.02s 
 
 0.020 
 
 0.02 
 
 0.02 
 
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 Excavation. — Under the term "excavation" as applied to canals 
 there is generally included all earthwork required for the construc- 
 tion of the canal, the formation of embankments, and such pther 
 incidental work as building approaches to culverts and bridges and 
 the backfilling around structures. 
 
 The excavation of canals, on account of the relative magnitude 
 of the work, is one of the most important factors in the construc- 
 tion of an irrigation system. The fundamental questions involved 
 
48 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 in excavation are those of cost and the determination of methods by 
 means of which the most satisfactory and economic results can be 
 obtained. There are also involved the measurement and classi- 
 ficatiorl of the materials excavated and the direction of the work in 
 such a manner that the canal when completed will serve as a per- 
 manent waterway with a minimum loss by seepage and cost for 
 maintenance. Excavation from canals is commonly done either by 
 teams or some form of power excavating machinery. The advantage 
 of either of these methods over the other depends largely upon the 
 character of materials to be handled and the local conditions affecting 
 the work. Where work is scattered over a considerable area, as 
 is the case with small canals, it is ordinarily done to best advantage 
 by means of teams and scrapers, or some form of portable excavator 
 which can be handled by teams or traction engines as shown in 
 Plate III. 
 
 When the work is concentrated at one point so as to require but 
 little moving of machinery, as is the case in excavating large canals 
 or making deep cuts, heavy excavating machinery, such, for example, 
 as steam shovels, drag-line scrapers, or dredges are more economical 
 and permit of better progress being made than the use of teams. 
 The amount of work to be done must also be considered in determin- 
 ing the most economic and feasible method. For a small job 
 where the cost of installing a plant forms a large proportion of the 
 total cost of the work the unit cost by means of machinery may 
 exceed what it would have been with a less expensive equipment, 
 even though the latter is less efficient in character, while for a large 
 job the cost of installation of the more expensive and efficient 
 machinery could have been distributed over a large amount of work 
 and the unit costs correspondingly decreased. (See Plate IV, Figs. 
 A and B.) 
 
 The distance which material has to be moved is also important 
 in determining the method to be used. For team work, where the 
 haul does not exceed from loo to 200 ft. Fresno scrapers, drawn by 
 four horses, have been found to be the most efficient, while for 
 greater distances preference is given to other types, as for example, 
 the wheel scraper. The advantage of the latter is that the hauling 
 which consumes the greater part of the time can be done with a less 
 number of animals than is required by any form of drag scraper. It 
 is customary in long hauls to use extra animals for loading and de- 
 tach them when the loading is completed, allowing one team to 
 transport the load to its destination. (See Plate II.) 
 
Plate TIT 
 
 Fig. a. — Constructing canal in earth by means of four-horse Fresno scrapers. 
 Minidoka Project, Idaho. 
 
 
 
 
 
 
 
 Fig. B. — Throwing up small laterals by means of four-horse road machine. 
 
 Huntley Project, Mont. 
 
 {Facing Page 48) 
 
Plate TIT 
 
 Fig. C. — Excavating canal by use of excavator with belt conveyor, drawn by 
 traction engine. Belle Fourche Project, So. Dak. 
 
 Fig. D. — Finished canal with both upper and lower banks. Lower Yellowstone 
 
 Project, Mont. 
 
DESIGN AND CONSTRUCTION OF CANALS 49 
 
 In building embankments team work has an advantage over other 
 methods on account of the consolidation of the embankments due 
 to the tramping of the animals. When embankments to hold water 
 are built by other methods it is necessary to adopt some means of 
 compacting the earth. The most common way of doing this is by 
 means of rolling or tamping. On account of the difficulty of rolling 
 small banks teams for this class of work are usually favored. 
 
 It must be remembered that each particular job of excavation 
 differs in some particulars at least from other jobs of similar work, and 
 that methods which have proven entirely satisfactory in one case may 
 be wholly unsuited to another job. For this reason it is impossible 
 to say in general that one method is superior to another. In estimat- 
 ing the cost of work by a particular method the safest plan is to 
 compare it with the cost of similar work elsewhere, allowance being 
 made for difference in local conditions. Results obtained in this 
 manner are likely to prove far more satisfactory than those based 
 upon theoretical considerations. 
 
 As a basis for estimates, and the fixing of prices for handling 
 different kinds of materials, it is customary to divide excavation into 
 classes. One method of classifying is by natural designations, such, 
 for example, as earth, hard pan, loose rock, solid rock and similar 
 terms. A second method is to classify the materials according to 
 the way in which they can be handled, as, for example, materials 
 which can be plowed, and those which require drilling and blasting. 
 Both methods are to a certain degree inexact and leave a great deal 
 to the judgment of the engineer. 
 
 In attempting to use the method first named it is sometimes 
 impossible to draw a sharp line of demarcation between the different 
 materials. The distinction between earth and hard pan or even 
 between earth and rock is not always easily determined on account 
 of the blending of one class of material into the other. It sometimes 
 happens that proper classification according to such designations 
 can be made only by a trained geologist. Such geological classifica- 
 tion may have little practical value as a measure of the amount of 
 work required in excavation. Some material properly defined as 
 earth may be more dif&cult and expensive to remove than other ma- 
 terial which may be properly termed rock. 
 
 The second method of classification according to some assumed 
 mechanical operation avoids the use of vague terms, and may depend 
 more nearly upon the amount of work, and the resultant cost 
 thereof, which will be required. For example, material which can 
 
 4 
 
50 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 be plowed can ordinarily be handled with less effort and at a lower 
 cost than material which has to be loosened by blasting or other 
 expensive operations. This method of basing classification upon 
 well-known and clearly defined operations for loosening or handhng 
 materials has been found the more satisfactory. Differences of 
 opinion relative to such a classification can ordinarily be tested by 
 simple operations on the work, thus avoiding definitions which may 
 depend upon fine technicalities. 
 
 Specifications for Excavation. — The construction of canals, 
 whether to be done by contract or by hired labor which is directly 
 under the control of the engineer, should be done in accordance 
 with definite plans and specifications. For contract work specifica- 
 tions are necessary to define exactly what is covered by the contract 
 and avoid all misunderstanding, and where the work is being per- 
 formed directly by hired force they' are of nearly equal importance 
 as a guide to the superintendents and others in carrying out the 
 work. The specifications with the plans of the work should be 
 sufficiently complete to answer all ordinary questions relative to 
 the operations such as methods of measurement, payment, classi- 
 fication of materials, and how the work shall be handled. The 
 following specifications, modified when necessary to meet special 
 conditions, are in use by the U. S. Reclamation Service: 
 
 (a) Classification. — All material required to be excavated in 
 connection with the construction of the canal will be measured in 
 excavation and classified for payment as follows: 
 
 Class I. All material that is loose and can be handled with 
 scrapers and all material that can be plowed by a six-horse team, 
 each animal weighing not less than 1,400 lb., attached to a suitable 
 plow, all well handled by at least three men; also all loose rocks 
 in pieces not exceeding 2 cu. ft. in volume occurring in loose material 
 or in material that can be thus plowed. 
 
 Class 2. All material not included in Classes i and 3. 
 
 Class 3. All rock in place that cannot be removed without the 
 use of powder and all detached masses of rock exceeding 10 cu. ft. 
 in volume. 
 
 (b) Canal Section. — The canal and embankment sections are 
 shown in the drawings, but the undetermined stability of the 
 material that will form the canal banks may make it necessary 
 during the progress of the work to vary the slopes and the dimension 
 dependent thereon. Variations of this character will not entitle 
 the contractor to pay at any other rates than those named in the 
 
DESIGN AND CONSTRUCTION OF CANALS 51 
 
 contract. The canal shall be excavated to the full depth and 
 width required and must be finished true to line and grade in a 
 workman-like manner. Earth slopes shall be neatly finished with 
 slip scrapers or other suitable appliances. Rock bottoms and banks 
 must show no points of rock projecting more than 0.3 ft. in the 
 prescribed section. Above the water line the rock will be 
 allowed to stand at its steepest safe angle, and no finishing will be 
 required beyond removal of rock masses that are loose and liable 
 to fall. 
 
 (c) Material to he Laid Aside. — Whenever directed by the engineer 
 materials found in the excavations such as sand, gravel or stone 
 that are suitable for use in structures or that are otherwise required 
 for special purposes shall be preserved and laid aside in some con- 
 venient place designated by him. 
 
 (d) Material for Canal Embankments. — All suitable material 
 excavated within the prescribed canal lines will be avaOable for 
 embankment construction. So much thereof as may be needed 
 shall be placed in the embankment where directed by the engineer. 
 Where this source of material is inadequate additional material 
 may be obtained from borrow pits whose location will be subject 
 to the approval of the engineer. Unless the engineer gives the 
 contractor specific written orders to excavate other than Class i 
 material from borrow pits for embankment construction all material 
 obtained from this source for such purpose will be paid for at the 
 unit price bid for Class i regardless of its actual character. 
 
 (e) Construction of Embankments. — The ground under all embank- 
 ments that are to sustain water pressure shall be cleared of brush, 
 trees and roots. The foundation surface shall be well plowed. 
 Should the engineer direct that unsuitable material be excavated 
 and removed from' the site of the embankment the material thus 
 excavated will be paid for as excavation. All material deposited 
 in embankments that are to sustain water pressure shall be thor- 
 oughly compacted. The compacting must be equivalent to that 
 obtained by trampling of well-distributed scraper teams depositing 
 the material in layers that are 6 in. thick when compacted. 
 
 (f) Runways. — Runways shall not be cut into canal excavation 
 slopes below the proposed water level. 
 
 (g) Blasting. — Any blasting that would injure the work will 
 not be permitted. If the slopes are shattered or broken by blasting, 
 such places shall be excavated to firm material, and the holes thus 
 made shall be filled to grade or slopes with such material and in 
 
52 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 such manner as the engineer may designate, all at the expense of 
 the contractor. 
 
 (h) Excess Excavation. — Material excavated for the canal in 
 excess of that required for canal embankments shall be used for 
 the widening of the embankments as may be directed by the engineer. 
 Material taken from cuts that is not suitable for embankment 
 construction and other material not required for embankments or 
 embankment widening may be wasted on the right-of-way owned 
 by the United States, provided it is not deposited in drainage 
 channels nor within 25 ft. of the edge of the canal cut. 
 
 (i) Overhaul.— In hauling excavated material required for embank- 
 ments or other useful purposes or for lajdng aside for subsequent 
 use, 200 ft. will be considered the limit of free haul and any haul 
 in excess of this distance will be termed overhaul. Whenever the 
 engineer requires such material to be hauled more than 200 ft., 
 the contractor will be paid for overhaul at the rate of one and one- 
 half cents per cubic yard per 100 ft. for the haul in excess of 200 ft. 
 No overhaul of material wasted will be paid for. 
 
 (j) Measurement and Payment. — Measurement will be made 
 to the neat lines of the excavation as shown on drawings or staked 
 out by the engineer. Payment for excavation will be made at the 
 unit price bid therefor which shall include the cost of all labor 
 material and supplies incident to excavating and placing the material 
 in embankments, preparing surface, spreading, rolling, tamping, etc., 
 required to complete the work in accordance with the specifications. 
 
 Protection Against Seepage in Canals. — The losses of water in 
 transmission in a canal system, especially one recently constructed, 
 form a notable proportion of the amount of water received into 
 the canal. Careful observations and studies should be made of 
 these losses in order to ascertain where they are taking place and 
 to take measures for their correction, not merely to prevent the 
 loss of the water which is valuable in itself, but to keep this seepage 
 water from ruining lands in the vicinity. The amount of these 
 losses is illustrated by the accompanying figure which gives for 
 comparison the total diversions from the river in each case, and the 
 proportion of this which is lost in transmission. 
 
 The accompanying figure (12) gives for the months of April to 
 September or October the quantity of water which was received 
 into the canal, this being indicated by the vertical spaces and the 
 quantity which is lost in transit. This is classified in most cases 
 into the losses in the main canal and those in the lateral system. 
 
DESIGN AND CONSTRUCTION OF CANALS 
 
 53 
 
 Fig. 12. — Diagram illustrating relative quantities of water used, and lost 
 in laterals and in main canals of various projects during the crop season 
 of igii. 
 
54 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 It is to be noted that in general the losses are in proportion to the 
 quantity diverted, although theoretically at least the losses during 
 the early part of the season should be greater in proportion to those 
 later on. 
 
 Where it is necessary to use unsatisfactory material for the con- 
 struction of canal banks, or where canals are excavated in loose or 
 porous material, special precautions have to be taken against loss of 
 water by seepage. Seepage from canals may be either through the 
 sides and bottom under the artificial banks, or through the embank- 
 ments themselves. Where it is of the first form it frequently pene- 
 trates to some depth in the natural material and comes to the surface 
 at a considerable distance from the canal. Seepage of this kind is 
 the most difficult to prevent. It can sometimes be avoided by cut- 
 ting a deep trench underneath the canal embankment and filling it 
 with puddle or other impervious material. Where this method is 
 employed it is necessary to carry the core down to impervious 
 material which can frequently be done on side-hill work. 
 
 Another method of preventing seepage is to cover the slopes and 
 bottom of the canal with fine material, such as soil or loam, which, 
 when acted upon by the water is carried into the interstices of the 
 material below in time forming a water-tight film along the surface. 
 
 The remedies for seepage through artificial banks are practically 
 the same as those above mentioned, i.e., by constructing a core of 
 puddle or other impervious material in the center of the bank, or by 
 lining the inner slope with soil or other fine material. 
 
 Where a canal is lined to prevent seepage, care must be taken in 
 future maintenance and cleaning of the canal to avoid removing 
 or breaking into this thin layer of water-tight material. 
 
 In the construction of canals much can be done to prevent seepage 
 through the banks by requiring that the coarse material be placed 
 on the outer portion and the finer material on the inner side of the 
 banks. In the construction of canals in cold climates, especial care 
 should be taken to see that material is not deposited while the mate- 
 rial or the embankment is frozen. When in a frozen condition, 
 material, especially if it be moist, occupies a greater space than after 
 it is thawed, and in the process of thawing is likely to leave small 
 openings through which water can escape. 
 
 Another method for preventing seepage which is sometimes re- 
 sorted to is by lining the canal either with masonry, plaster or 
 lumber. 
 
 On one of the Reclamation Service canals, where it was necessary 
 
Plate IV 
 
 Fig. a. — Enlarging canal by means of floating dipper dredge. Salt River 
 
 Project, Ariz. 
 
 Fig. B. — Enlarging canal by use of excavator with drag-line working from one 
 
 side of canal. Salt River Project, Ariz. 
 
 (Facing Page 54) 
 
Plate TV 
 
 Fig. C. — Lining canal with concrete to increase the capacity, and reduce the 
 seepage. Boise Project, Idaho. 
 
 Fig. D. — Concrete lined canal in shattered rock, carrying water of Triickee River 
 to Carson River. Truckee-Carson Project, Nev. 
 
DESIGN AND CONSTRUCTION OF CANALS 55 
 
 to carry water through a canal constructed on a large fill, a temporary 
 lining of lumber was constructed to be used until the embankment 
 should become thoroughly settled. The future plans provide that 
 when such settlement has taken place and the lining must be re- 
 newed it will be replaced by some form of permanent material. 
 
 Seepage sometimes results from erosion of banks by which the 
 finer material along the surface is carried away. This is most likely 
 to occur on the outer slope around curves. 
 
 Lined Canals. — In the construction of canals a permanent lining 
 of concrete is frequently used. The purpose of such a lining is two- 
 fold; first, to prevent seepage where a canal is constructed in porous 
 material; and second, to increase the velocity and thus reduce the 
 section of the canal where deep cutting is required. If, for example, 
 a canal is to be constructed to a depth two or three times that of the 
 depth of the water it is frequently cheaper to excavate a smaller 
 section and line the lower wetted portion than to excavate a canal 
 having the required capacity in earth section. Where concrete 
 lining is used, it is economical to make the side slopes as steep as 
 possible. As shown on page 39, the most advantageous section 
 theoretically is one with vertical slopes. This, however, is impracti- 
 cable. It frequently happens, however, in deep cuts that material 
 will stand on as steep slopes as 1/2 horizontal to i vertical, which 
 is a section very commonly used in lined canals. In placing the 
 lining in canals with slopes as great as 1/2 to i, it is ordinarily neces- 
 sary to use forms on the inner slope, filling in the concrete between 
 the forms and the earth or rock banks. Where the excavation is 
 taken out beyond the neat lines this space can be backfilled with 
 loose rock. In placing lining on slopes i horizontal to i vertical, 
 or flatter, it is possible to do the work without the use of forms. 
 (See Plate IV, Fig. 6.) 
 
 Canal linings are usually constructed in slabs of from 10 ft. or more 
 in width built in alternate sections so as to provide expansion joints 
 and prevent temperature cracks. Paper, or a thin painting of oil, is 
 sometimes applied to the edge of the slabs to prevent the concrete 
 bonding. This protection, however, is ordinarily unnecessary if the 
 concrete in the first slabs is allowed to set before the second is put in. 
 The thickness of concrete used for a permanent canal lining varies 
 from 3 to 6 in., depending upon the steepness of the slopes, the 
 nature of the material, and climatic conditions. Freezing has a 
 tendency to loosen the lining from the banks by the expansion due 
 to crystallization of the small amount of water in the earth. In a 
 
56 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 cold climate, where freezing is likely to penetrate the lining, the 
 customary thickness for conditions of this kind is about 6 in. In 
 climates where frost is not prevalent a less thickness is sufficient. 
 Linings sometimes fail on account of the pressure exerted by water 
 which collects behind them. This can be relieved by putting weep 
 holes through the bottom of the hning at frequent intervals. The 
 construction of weep holes is also an additional protection against 
 frosts as they keep the material back of the lining drained and re- 
 duce the amount of expansion when freezing occurs. 
 
 Fig. 13. — Cement lined canal witi reenforced concrete arch cover later added 
 to catch the loose, sliding debris from steep hill slopes, Strawberry Valley Proj- 
 ect, Utah. 
 
 Roadways on Banks.— Roadways on the banks of canals have cer- 
 tain advantages, in that they permit of easy access to the canal for 
 operation and maintenance purposes. In highly cultivated areas, 
 where land is valuable, there is a saving of the land that would 
 otherwise be required in the location of highways. There is also a 
 certain gain due to the compacting effect of travel on the banks. 
 This latter, however, is of little value except on new canals. 
 
 The disadvantages of roadways constructed on canal banks are 
 that with certain materials the traffic has a tendency during the dry 
 season to break up the surface layers into dust, rapidly carried away 
 
DESIGN AND CONSTRUCTION OF CANALS 57 
 
 by the winds. There is a tendency also to wearing down of the 
 banks into ruts which, during the rainy season, become filled with 
 water which finally breaks over the banks and causes erosion of the 
 slopes. 
 
 The practicability of constructing roadways on the banks of 
 canals in general depends upon the local conditions, all of which 
 must be taken into account in determining the proper course to 
 pursue. Where roadways are constructed on banks it is necessary 
 to make the top width somewhat greater than would be required if 
 such roadways were not built. In ordinary materials banks made 
 with a top width of about lo ft. are usually strong enough to with- 
 stand the water pressure. Where a roadway is required on the 
 bank, the top width should be not less than 12 ft. and preferably 
 from 14 to 16 ft. In a climate where snow and ice prevail during a 
 portion of the year roadways upon banks, except of considerable 
 width, are dangerous and should be avoided for public travel. 
 
 Lateral Drainage. — In order to provide full protection for a canal, 
 especially when located on sloping ground, it is necessary to provide 
 for the care of lateral drainage. This feature, if neglected, may 
 cause pools to form above the canal and, in periods of extreme 
 rainfall, may result in an overtopping of the banks. The amount 
 of lateral drainage which must be taken care of is a question some- 
 what difficult to determine. Especial study must be given to each 
 particular case. The most satisfactory method of determining the 
 amount of lateral drainage in a particular waterway is by past 
 records of the quantity of flow. Information of this kind, however, 
 is generally lacking, as flood conditions in ravines or smaU streams 
 which are to be crossed by an irrigation canal are generally not 
 observed. It is sometimes possible to determine from water marks 
 the area of cross-section of a stream and from the general slopes of 
 the country to form some estimate of the velocity and corresponding 
 amount of discharge. Where such data are available they serve as 
 a guide in determining the amount of drainage water which must be 
 cared for. 
 
 Where all information relative to flow is lacking an estimate of 
 the amount of runoff can be made from the catchment area, assuming 
 a maximum rainfall per square nule. The amount of rainfall which 
 must be assumed in this case will vary greatly in different parts of 
 the country. The size of the drainage area is also a factor in deter- 
 mining the runoff per unit area, since, on small areas, the water is 
 more quickly collected and approximates more closely to the total 
 
58 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 amount of rainfall on the area. For small areas, say, for example, 
 from 1 to 5 square miles, the maximum runoff for a given period may 
 reach approximately the total amount of water falling on the catch- 
 ment area during the period. This, however, is exceptional. In 
 providing for lateral drainage for the protection of canals it is neces- 
 sary to consider extreme cases, and good practice demands that 
 errors be on the side of safety in providing for a greater runoff 
 than is necessary, rather than one which is too small for maximum 
 conditions. 
 
 Lateral drainage may be cared for by diverting the water into the 
 canal, or carrying it under or over the canal. The method which is 
 most desirable in any particular case will depend upon local condi- 
 tions. Where the quantity of lateral drainage is small and where 
 it does not occur during the irrigation season it is frequently possible 
 to carry it into the canal and dispose of it through some wasteway 
 into natural channels. When lateral drainage must be provided 
 for during the irrigation season this method is unsafe on account 
 of the danger of exceeding the capacity of the canal. The method 
 of diverting drainage into a canal is ordinarily by means of a flume 
 or shallow channel down the upper slope of the canal. 
 
 Where the quantity of drainage is not excessively large, it may be 
 diverted under the canal by means of a siphon or culvert. This 
 method is particularly well adapted to locations where the canal 
 is constructed in fill thus permitting a siphon or culvert to be con- 
 structed beneath the canal with a minimum amount of excavation. 
 The upper bank in such a case also provides a small amount of 
 storage which helps to control the drainage water. The filling up 
 of the depression above the canal also raises the head on the cul- 
 vert or siphon and increases its capacity during a flood. 
 
 Where large quantities of drainage water must be taken under a 
 canal a common practice is to carry the canal in a flume supported 
 by means of a suitable bridge or trestle work. In the location and 
 design of a structure of this kind especial care should be taken to 
 see that the opening below the structure is sufficiently large to 
 provide for the maximum flow. A good example of a large canal 
 being carried across a draw is the Spring canyon flume on the North 
 Platte project, Nebraska. Here a canal of i ,400 second-feet capacity 
 is carried over a canyon by means of a concrete flume supported by 
 three reinforced concrete arches. The span of the largest arch is 50 
 ft. and the total distance spanned no ft. (See Plate VII, Fig. A.) 
 
 The third method of caring for lateral drainage, by taking it over 
 
DESIGN AND CONSTRUCTION OF CANALS 59 
 
 a canal, may be accomplished by employing a flume or other struc- 
 ture for carrying the drainage water, or by carrying the canal 
 beneath the natural drainage channel by means of an inverted 
 siphon. 
 
 In general, where the quantity of lateral drainage is small, it may 
 be taken care of by drainage into the canal or by a flume or culvert 
 constructed either under or over the canal. Where the quantity 
 large, however, or where the drainage area is considerable in amount, 
 the better and safer plan is to allow the drainage to follow its natural 
 waterway and to divert the canal either under or over the stream. 
 
 Right-of-way for Canals. — The cross-section and location of a 
 canal having been fixed, the width of right-of-way required can be 
 determined. On account of the ordinarily high values of irrigable 
 lands it is desirable that no more be taken for right-of-way than is 
 necessary, whUe, on the other hand, it is essential that suflScient 
 width be procured to permit economical operation and maintenance. 
 The width of right-of-way required depends, to a great extent, upon 
 the size and importance of a canal. For main canals the right-of- 
 way should be wide enough to include all embankments and in gen- 
 eral with sufficient additional width to permit of work being done 
 on these embankments without trespassing on adjacent property. 
 
 The right-of-way should provide, especially in the vicinity of 
 embankments, a certain amount of space which can be used for bor- 
 row pits in case of emergency. The successful operation of a canal 
 system or of a canal may depend upon having immediately avail- 
 able material for making repairs. Unless provision is made for this 
 when the original right-of-way is acquired, there is no assurance 
 . in future years that needed material can be had at once. As lands 
 are irrigated and the country becomes more thickly settled the value 
 of land and the difficulties of acquiring additional right-of-way 
 increase correspondingly. 
 
 The right-of-way for small and less important canals may be 
 narrower than for larger canals. In every case, however, the right- 
 of-way should be sufficient to provide for access along the canal for 
 repairs and for needed materials for maintaining fills. For a small 
 lateral, located practically all in cut and over comparatively level 
 ground, the only right-of-way required in addition to the waterway 
 is that necessary for travel along the canal. The same size canal 
 located upon uneven ground or over a high fill would require a con- 
 siderable amount of additional right-of-way in order to provide for 
 material for repairing breaks in case of emergency. 
 
60 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 There can be no fixed rule laid down as to the width of right-of-way 
 which is required for any particular size canal. It must be kept in 
 mind that for successful operation it is necessary to have unrestricted 
 access to every portion of the canal system, and that for economical 
 maintenance there is need of sufficient room for operation and of 
 material for repairing breaks in case of an emergency. 
 
 Rights-of-way are of two classes: first, those which permit of the 
 land being used for canal purposes, the fee or actual title thereof 
 remaining with the original owner; and, second, ownership in fee 
 simple. Ordinarily a title to a right-of-way which permits of the 
 construction and operation of a canal only is objectionable, on account 
 of certain rights which the original owner of the land may have 
 thereto. For this reason it is believed that rights-of-way for main 
 canals should be purchased outright so that the canal owners will be 
 free to handle the construction and future operation and mainte- 
 nance without restriction. 
 
CHAPTER V 
 
 CANAL STRUCTURES 
 
 Classification. — Under the term "Canal Structures" are usually 
 included all appurtenances outside of the main waterway of the canal 
 together with any devices necessary for carrying the main waterway 
 over or under streams, such, for example, as flumes, siphons, etc. 
 In accordance with the purpose for which they are intended, canal 
 structures may be classified under three heads, as follows : 
 
 1. Structures for diversion and controlling of water. 
 
 2. Structures for protection. 
 
 3. Miscellaneous structures. 
 
 Under the first classification, structures for diversion and control- 
 ling of water, are included head gates, which regulate the amount 
 of water diverted into a canal; turnouts, for controlling and regu- 
 lating the amount of water diverted from a canal, and checks and 
 drops, which regulate the surface elevation of water in a canal. 
 
 Under the second classification, structures for protection, are 
 included wasteways for discharging excess waters from a canal to 
 prevent its being burdened above its normal capacity and also for 
 emptying the canal in cases of emergency. There are included in 
 this class also culverts and other structures intended to remove excess 
 waters from the canal and prevent the banks being overtopped. 
 
 Under the head of miscellaneous structures are included bridges 
 and like structures made necessary by the presence of the canal. 
 Structures of the latter class may or may not have a part in the op- 
 eration or maintenance of a canal and are not necessarily a part of 
 the canal system. They are necessary, however, for the use of 
 individuals or the public in general to compensate for the inconveni- 
 ence caused by the construction of the canal and must therefore be 
 considered as a part of the appurtenances of such canal. 
 
 Permanent and Temporary Structures. — Canal structures are 
 sometimes also classified as temporary and permanent. A perma- 
 nent structure is one, the location and duties of which are sufficiently 
 well known, that can be built of lasting materials and in such a man- 
 ner as to serve during the life of such materials. A temporary struc- 
 ture is one, the location or purpose of which has not been definitely 
 
 61 
 
62 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 determined or one which on account of future developments, will 
 be rendered useless and can be removed at the end of a short period. 
 
 In the laying out and construction of distribution systems it is 
 frequently advisable to provide temporary measures for delivering 
 water on certain areas before final work is completed. In such cases 
 the use of temporary structures is justifiable. It frequently happens 
 also that changes in the methods of irrigation wiU be made, which, 
 when effected, will require different modes or points of delivery. 
 In such cases the use of temporary structures is also justifiable. 
 
 In the design and location of structures, especially those pertain- 
 ing to the delivery of water, it must be remembered that irrigation 
 is not yet developed to the point of an exact science and that specific 
 cases wUl be encountered upon which we have little or no previous 
 experience and where the choice between two different methods is 
 difficult. In cases of this kind it is frequently justifiable to construct 
 works of a temporary character to be utilized in a somewhat experi- 
 mental manner until the proper data for location and construction 
 of permanent works can be obtained. Except in such cases as above 
 mentioned, which it is believed are generally rare, structures so far 
 as consistent with cost should be made of as permanent a character 
 as possible in order that they may afford ample protection to the 
 system during the period of its operation. 
 
 Headgates. — The function of a headgate is to control and regu- 
 late the discharge of water into canals. The term "headgate" is 
 generally applied to the larger structures, such, for example, as 
 those at the head of main canals or laterals. The requirements 
 for headgates for a canal are as follows: First, they shall be strong 
 enough to withstand the maximum pressure and head of water 
 which is imposed upon them; second, they shall have sufficient 
 capacity to divert the maximum flow of the canal; third, they shall 
 permit of regulation sufficient to control with accuracy the quantity 
 of water being diverted. 
 
 In the design of a headgate first consideration should be given 
 to the question of its stability. On a large or important canal the 
 headgates serve as a protection for the canal system and property 
 thereunder. On account of this important function no pains shoidd 
 be spared in the design and location of such structures to make them 
 absolutely safe, and of as permanent a character as is consistent 
 with reasonable expenditure. Permanent headworks on important 
 canals are usually constructed of masonry, the ordinary type of 
 design being some form of gravity structure amply heavy to 
 
Plate V 
 
 «!^^ A . 
 
 Fig. a. — Wooden headgates, typical of those usually built for the earlier canals. 
 Jordan and Salt Lake City Canal, Utah. 
 
 l^„•W^C%*; 
 
 ,i. 
 
 
 Fig. B. — Concrete headworks with steel gates. Interstate canal, North Platte 
 
 Project, Nebr. 
 
 {Facing Page 62) 
 
Plate V 
 
 i-t^di. 
 
 Fig. C. — Concrete headworks and roadway, Mesilla Valley canal. Rio Grande 
 
 Project, N. Mex. 
 
 Fig. D. — Concrete headworks with sluice gates at Laguna dam on Colorado 
 
 River, Ariz.-Cal. 
 
CANAL STRUCTURES 
 
 63 
 
 Section E-F 
 
 Fig. 14.— Head-works for Interstate Canal, North Platte Project, 
 Wyoming-Nebraska. 
 
64 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 bo 
 
 P4 
 
 o 
 
 CO 
 
 "3 
 
 m 
 
 
 
 
CANAL STRUCTURES 65 
 
 resist overturning with the maximum head which may be imposed 
 upon it. 
 
 Another important factor in the design and construction of head- 
 works is to provide sufficient curtain and wing walls to prevent 
 seepage either under or around the structure. The extent of such 
 protection against seepage will depend upon the amount of head and 
 the character of material in which the structure is placed and no 
 general rules can be laid down for designs of this kind. It is, however, 
 essential that a complete study and investigation be made in each 
 particular case. 
 
 In backfilling around headgates the greatest care should be given 
 both to the character and manner of compacting the material. 
 Under ordinary conditions the greatest degree of compactness can 
 be obtained by the use of water, that is, by either wetting the mate- 
 rial to a slight degree and tamping it or by depositing it in water. 
 
 The capacity of a headgate should be computed not only for the 
 maximum capacity of the canal but for various stages of water both 
 above and below the headgates. It is frequently necessary, espe- 
 cially where a water supply is limited, to operate a canal at part 
 capacity. Where this is necessary a headgate should be so designed 
 that the full capacity of the canal up to any level can be drawn from 
 the source of supply without undue loss of head at the structure. 
 In determining these functions it is necessary to consider both veloc- 
 ity and entry head and the entry coefficient. These principles 
 apply especially where diversions are made from fluctuating heads 
 as, for example, from streams without ample diversion weirs. 
 
 Operating Device. — The essential characteristics of the operating 
 device are that it be simple in operation and capable of controlling 
 accurately the amount of the discharge. Various forms of control- 
 ling devices are in use. They vary from the simple flash boards 
 which may be operated by hand to carefully designed and con- 
 structed metal gates operated by means of electric or other power. 
 On account of the difficulty of operation, the flash-board control is 
 not recommended for important diversion points. 
 
 The type of controlling apparatus which appears most satis- 
 factory for main canals and which is rapidly replacing the older type 
 of flash board or wooden gates recently built in inigation systems 
 is some form of metal gate operated by a screw driven by hand or 
 machine power as shown in Fig. 15. The advantages of a device 
 of this kind are that it is susceptible of a slight motion and furnishes 
 the means for regulatign to any desired quantity. Whether or not 
 5 
 
66 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 power is necessary depends upon the amount of energy necessary to 
 be expended and the time required for opening or closing the gates. 
 A satisfactory conclusion on this point can be made only by careful 
 computations. To take a concrete example, we will consider a gate 
 5 ft. square, subjected to a maximum head of 20 ft. at its central 
 point. The total pressure on the gate wUl be ^ = 62.5X25X20 = 
 31,250 lb. Assuming the coefficient of friction between the gate 
 and guides to be 0.25, the total force, exclusive of the weight of the 
 gate and stem, required to start it from a position of rest will be 0.25 
 X31, 250 = 7, 812. 5 lb. To raise this gate at the rate of i ft. per 
 
 Top Flan 
 
 FIatfotm\ 
 
 Front Elevation of Gate Leaf 
 
 Cast l»n Seat Qroutfld in Conaiet« 
 
 Longitudinal Section 
 
 Fig. 16. — Electrically operated sluice gates, Salt River Project, Arizona. 
 
 minute, if we assume the weight of the gate to be say 3,000 lb., will 
 require the expenditure of 10,800 ft.-lb. of energy per minute or 
 approximately 1/3 h.p. 
 
 In some cases, where the water supply carries large quantities of 
 silt in suspension which it is desirable to prevent entering the canals, 
 special forms of headgates or diversion works are used. The most 
 common method of preventing silt from entering the canals is by 
 skimming the water from the surface thus leaving the heavy silts 
 
CANAL STRUCTURES 67 
 
 which are carried nearer the bottom undisturbed. To accomplish 
 this, flash boards, the top portion of which can be removed, or gates 
 which can be lowered so as to allow the water to pass over them, are 
 used. Where this form of diversion is employed it is necessary to con- 
 struct sluice gates for removing the silts which are deposited above 
 the headgates. These sluice gates, in order to be effective, should be 
 placed near the diversion gates and should also be at a considerably 
 lower elevation. 
 
 The diversion works at theLagima Dam near Yuma, Arizona, shown 
 on Plate V, Fig. D, consist of a series of overflow gates of suflScient 
 width that the supply is drawn from the upper 4 ft. of the pool above 
 the dam. The accumulated silts are removed by means of sluice- 
 ways, the bottoms of which are approximately 13 ft. below the top of 
 the dam. These sluiceways are controlled by means of electrically 
 operated gates each having a clear opening of 33 ft. 4 in. wide. 
 
 Turnouts. — Under the term "turnout" are included structures 
 for diverting water from the main canals and laterals to the dis- 
 tributaries and farm ditches. The most common form of turnout, 
 and one which seems most satisfactory, consists of a box or pipe 
 opening through the bank of the main canal and controlled on the 
 inner side by a gate or flash board. To provide for drawing a supply 
 from the canal when it is only partly filled, turnouts should be lo- 
 cated as low as possible. On account of the important position they 
 occupy, and the difficulties of renewing them, turnouts from main 
 canals should be of permanent construction. Where the amount of 
 water -to be diverted is considerable, a solid conduit of masonry or 
 concrete should be used as shown in Fig. 17; where only a small 
 opening is required vitrified or cement pipes laid with tightly 
 cemented joints are satisfactory as shown in Fig. 18. 
 
 In the placing of the turnout, cut-off walls should be constructed 
 around the conduit or pipe and the earth filling around them should 
 be carefully tamped or puddled in order to prevent seepage and a 
 possible washing out of the structure. Where very large openings 
 are required, as, for example, at the diversion to a large lateral, 
 masonry or concrete sluices, controlled by gates, are constructed 
 through the banks. The upper and lower ends of turnouts should 
 be protected by means of ample wing walls or heavy water-tight 
 paving on the slopes to prevent erosion and seepage. Each turnout 
 should be provided with a means of controlling the flow, so arranged 
 that it can be easily operated, and securely fastened in position. 
 
 On the older canals most of the turnouts as well as other structures 
 
68 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 were built originally of wood. A drawing of the details of one of 
 the ordinary wooden boxes is shown in Fig. 19. 
 Where the head on a turnout is considerable, say above 3 ft., it 
 
 ^11 
 III 
 
 H' 
 
 a is 
 
 111 
 
 
 
 Sl"- 
 
 s 
 
 yV"'""" 
 
 e^ ra 
 
 jO^ 
 
 
 
 ii I 
 
 
 
 
 
 
 c: 
 
 \ 
 
 
 •^ 
 
 
 
 
 
 
 > 
 
 
 
 
 
 
 
 NV 
 
 
 N 
 
 NS 
 
 
 ■H 
 
 ■3 \ 
 
 
 nl 
 
 !l 
 
 
 » 
 
 --PT--|-tf-l- 
 
 
 should in general be controlled by means of gates. For low heads, 
 flash boards may be used. They are, however, more or less unsatis- 
 factory in important structures on account of the difl&culty of regu- 
 lating the flow and the tendency to constant leakage. 
 
CANAL STRUCTURES 
 
 69 
 
70 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 The capacity of a turnout will depend upon the capacity of the 
 canal which it serves. It should be designed to furnish the required 
 amount of water with the minimum head in the main canal at which 
 
 a 
 H 
 
 it is to be operated. When the pipe or conduit is short, so that its 
 friction may be neglected, the velocity of flow through it may be 
 computed from the formula F = C\/2gA. Where h equals the head 
 in feet, g the force of gravity and C a constant depending upon the 
 shape of the orifice, but having an average value of about 0.8. 
 
CANAL STRUCTURES 71 
 
 Checks and Drops. — Checks and drops are used to regulate the 
 surface elevation and velocity of flow in canals. 
 
 The term "check" is commonly applied to a structure which closes 
 a part of the waterway of a canal and holds the water on its upstream 
 side at a greater elevation than on its downstream side. Checks are 
 sometimes built in the form of long-crested overflow weirs extending 
 across the canal and sometimes in the form of a structure carried well 
 up above the water surface and having an opening or openings 
 through which the water discharges. In each of these forms there 
 is a drop in the water surface in passing it. The chief purpose of a 
 check in a canal is to hold up the water surface at delivery points 
 while the canal is being operated at part capacity. This permits 
 water being delivered to lands which, in some cases, could not other- 
 wise be reached except with the canal running full. Checks are also 
 sometimes used to reduce grades and thereby lessen the velocities in 
 canals. 
 
 The term "drop" is applied to a structure through which water 
 is transferred from a higher to a lower elevation. Drops are used 
 where the slope of the country over which a canal passes is greater 
 than the allowable slope of the canal, the real purpose of the drops 
 being to reduce the effective grade or slope in the canal, and thereby 
 lessen its velocity by using up a portion of the grade in vertical or 
 nearly vertical falls. 
 
 The accompanying Fig. 22 gives the principal dimensions of the 
 ordinary drop built of timber such as has been employed on the 
 older canals. On the larger systems now being built throughout 
 the West these are replaced by concrete structures such as is 
 illustrated in Fig. 23. 
 
 Drops are commonly of two general types, classed as vertical or 
 inclined. In a vertical drop the water is allowed to fall freely, while 
 in an inclined drop it is carried down an incline by means of a chute 
 or some form of channel built of material not easily eroded. Water 
 in passing a drop acquires velocity which must be destroyed before 
 it enters the channel below, in order to prevent erosion. The most 
 common method of destioying this velocity is to allow the moving 
 stream to fall into a pool of water at the foot of the drop. The 
 pool in this case forms a water cushion which absorbs the energy of 
 the falling water. Water cushions may receive the stream either 
 vertical or at an angle inclined to the vertical. In the latter case 
 the impingement of the stream into the water below causes currents 
 
72 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 o 
 
 o 
 
 
 o 
 
 J3 
 
 •a 
 o 
 o 
 
CANAL STRUCTURES 
 
 73 
 
 which tend to serious erosion in the sides of the channel near the 
 foot of the structure. (See Plate VI, Figs. A and B.) 
 
 Rip-zap to Suit 
 Local ConditioDB 
 
 Removable Fla£b Boards 
 I'BiwrdB 2"pianl£a FootwalkJ 
 
 Upper Cut-off 
 
 VaU 2>lMikrfJ ^ 
 
 and 1 "Boards 
 
 £1. of Top of Bank above Drop 
 
 ^ Middle and Lower Cut-off 'Walte 
 
 2"PlBIlkB 
 
 Half Section A-A Half Section B-B 
 
 Planks 
 
 Section C-C 
 
 Fig. 2 2. — Type of timber drop for small canals. 
 
 In vertical drops there is a less tendency to erosion in the sides of 
 the channel. Since, on account of the absence of the horizontal 
 
74 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 component in the velocity, fewer currents are set up. There is a 
 tendency, however, in vertical drops for erosion to take place in the 
 bottom of the channel, where the stream impinges. The remedy 
 against erosion in either case is to provide sufficient width and depth 
 
 Fig. 23. — Type of concrete drop. 
 
 of water cushion to receive and absorb the shock of the falling water 
 without allowing it to impinge on the walls or bottom of the cushion 
 with sufficient force to injure them. Where a water cushion is to 
 receive any considerable velocity it should be built of masonry or 
 other permanent material. 
 
CANAL STRUCTURES 75 
 
 The size and depth of water cushion required for a given head and 
 quantity of flow are questions upon which engineers are somewhat 
 at variance, and experimental data for determining the proper 
 relations of these quantities is lacking. Some observations made in 
 India show that where the ratio of height of fall to depth of water 
 cushion is as 3 to 4, the flow had no injurious effects on the bottom 
 of the pool. So far as known, however, no careful set of observations 
 showing the relations between height of fall, quantity of discharge 
 and depth to which the effect of the stream is appreciable, have ever 
 been made. 
 
 In practice, water cushions are usually constructed with a depth 
 of about one-third that of the maximum fall, that is, one-third of 
 the height of weir above the surface of water below it, plus the 
 maximum depth of water flowing over the weir. It is believed 
 that for drops where the height of fall is not great this depth of 
 cushion is sufiB.cient. The length of cushion required will depend 
 somewhat upon the height of fall and quantity of water discharged. 
 It should be sufiScient to permit the water to come to a nearly quies- 
 cent state before it reaches the ordinary section of the canal below. 
 The minimum length of cushion should not be less than three or 
 four times its depth. The width of a cushion should be somewhat 
 greater than the length of the overflow weir. One of these incUned 
 drops or reinforced concrete chute designed to take the place of 
 ordinary drop on a steep grade is shown in Fig. 24 with water 
 cushion at the bottom. 
 
 With inclined drops of considerable height, a type of channel is 
 sometimes used which offers a large amount of resistance to the flow 
 of the water and prevents it acquiring a high velocity in its descent. 
 These channels are sometimes constructed of rough stones so placed 
 as to offer the maximum resistance to flow. In addition to the rough 
 walls and bottom, rock barriers projecting above the water surface 
 are placed at frequent intervals in the channel. Another and very 
 effective method of reducing velocity in an inclined drop is to con- 
 struct it in the form of a series of vertical drops with a water cushion 
 at the foot of each. By such a device the velocity is killed at each 
 water cushion and the maximum velocity which will be acquired will 
 depend upon the height of the secondary drops. 
 
 In the design and construction of drops for a canal over country 
 where the slope is considerable, it is necessary to do a large amount of 
 preliminary work in order to reach the most economical solution. 
 The principal points to be considered in this connection are the 
 
76 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 1 i-m 
 
 / " 
 
 " 
 
 I-KI \ 
 
 -/-- 1— V \ 
 
 -77S.S— ^ 
 
 *-!f—> 
 
 «-,7«,S 
 
 
 H 
 Is 
 
 
 
 I 
 
 
CANAL STRUCTURES 77 
 
 relative costs of a canal with fewer drops of greater height, compared 
 to one with more drops of lesser height. In the former case it must 
 be taken into account also that more excavation will be required on 
 account of the increased depth of the canal below the high drops. 
 In some cases where the slope of the country is very great it is more 
 economical to line a canal with masonry so that it will stand high 
 velocities, than to construct the necessary drops to reduce its veloc- 
 ity to a maximum for an earth canal. The latter method is in 
 efifect the construction of a long inclined drop. No general state- 
 ments can be made relative to the most economic method of handling 
 special cases, each must be considered in the light of all factors which 
 affect its efficiency and cost in order to reach a satisfactory solution. 
 (See Plate VI, Fig. C.) 
 
 Checks and drops are frequently combined in one structure, 
 which is, in fact, simply providing a means for holding up the water 
 in the canal above the drop. This may be done by a flash board or 
 gate regulation, the size of opening being adjusted to hold the water 
 up to the required height. The up-stream side of a drop is some- 
 times constructed as a weir with its crest raised some distance above 
 the grade of the canal. This weir automatically acts as a check for 
 holding the water up in the canal but has the disadvantages of 
 increasing the height of drop for low discharges and not permitting 
 the canal to drain completely. All drops of this kind should have a 
 small drain to completely unwater the canal. Immediately above 
 a drop which is given a free discharge there is a rapid drawing down 
 of the water in the canal and a corresponding increase in the velocity 
 of the flow. These high velocities have a tendency to destroy the 
 canal above a drop and if for no other reason than that of protection 
 it is ordinarily necessary to regulate the flow over a drop so that the 
 water above will not be drawn down to any appreciable extent. 
 One method of doing this is by means of the notched drop. 
 
 This notched drop (Fig. 25) is used extensively in India and 
 has been introduced in the United States. In this form of drop 
 the canal discharges from the upper channel into the pool below 
 through one or more notches of such size and shape that the amount 
 of flow through them for any given depth is very nearly equal in 
 amount to that carried by the canal with the same depth. A notch 
 which for all depths will theoretically discharge the same quantity 
 of water as will be carried by a trapezoidal canal section has curved 
 sides and bottom. Practically, however, this refinement is unneces- 
 sary, and a notch may be made with straight sides and bottom 
 
78 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 
 ^siPM JO iwaaa 
 
 
 o 
 12; 
 
 §• 
 
 ^ 
 
 o 
 
 a 
 
CAN4L STRUCTURES 79 
 
 which will fulfill practical requirements. The exact shape and 
 size of notch, that is the width of bottom and slope of the sides, 
 which is required, will depend upon the size and section of the 
 canal and must be designed for each particular case. With drops 
 of any considerable size it is preferable to use several notches 
 instead of one. This permits the water being broken up and dis- 
 tributed more nearly over the entire surface of the cushion below 
 and reduces its cutting effect. If a semi-circular lip be projected 
 for a short distance down-stream from the foot of each notch the 
 water can be further spread out and its erosive effect still further 
 diminished. (See Plate VI, Fig. B.) 
 
 Wasteways. — ^The term "wasteway" applied to canals, includes 
 two distinct classes of structures. The first, which is commonly 
 called an overflow spillway, is used to discharge the waters from a 
 canal when it becomes filled above its normal capacity. Such a 
 spillway is automatic in its action and serves as a safety valve to 
 prevent a canal being overloaded and its banks topped and washed 
 away. The second class of structures commonly known as a sluice 
 gate, is used for emptying a canal. Sluice gates in general are not 
 automatic in their action, but are ordinarily provided with the neces- 
 sary means for opening them quickly. They serve as a means 
 for rapidly drawing down the water in a canal in case of an emergency, 
 such as a break, or when repairs are necessary. 
 
 Overflow spillways and sluice gates are both to a large degree 
 protective in their nature; the first providing a safeguard against 
 accident, and the second a means for reducing the damage should 
 an accident occur. It cannot be said that the use of either is 
 absolutely necessary at a particular place in a canal, but experience 
 has shown that the protection which they afford to an important 
 canal is well worth their cost. 
 
 The requirements for location for the two classes of structures 
 do not differ greatly. In one important respect, that of requiring 
 a wasteway channel, they are similar. In other words, in the 
 location of either a spillway or sluice gate a site must be selected 
 from which it is possible to carry the waste water without undue 
 damage to the adjacent lands. On this account it is sometimes 
 feasible and economical to construct both a spillway and sluice 
 gates at the same point on a canal. The location of these structures 
 should be such that they are accessible and provide for the greatest 
 degree of efl&ciency. In general they should be located at or near 
 the lower end of that stretch of the canal they are intended to 
 
80 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 protect, since at this point the protection from overflow and the 
 drainage of a canal can be most easily effected. The frequency 
 at which the structures should be located is dependent upon the 
 size and importance of the canal. 
 
 In the design of an overflow spillway there must be considered 
 first the maximum quantity of water it shall discharge, and second, 
 the maximum rise above the normal elevation of water surface 
 which, the canal will stand. These factors are both uncertain and 
 may in some cases be classed as mere assumptions. In general it 
 may be assumed, however, that the maximum capacity of an over- 
 flow spillway need not exceed 50 per cent, of the capacity of a canal, 
 and that the maximum rise of water in the canal should not exceed 
 from 30 to 50 per cent, of the minimum free board. 
 
 Having established the discharge and head of water available, 
 the length of spillway required may be computed from the weir 
 formulae by selecting the proper coefficient for the particular form 
 of weir crest to be used. The form of weir crest and channel to be 
 used will depend to a great extent upon the topography of the site 
 and the character of the material. Spillways should as a rule be 
 located where the canal is well in cut in order to provide safe founda- 
 tion for the overflow weir and waterway leading from the weir over 
 the banks. This waterway should be water tight and for safety 
 should be of permanent masonry construction. 
 
 For collecting the discharge from a long weir and concentrating 
 it in a channel of small width various methods have been used. One 
 is to construct the upper portion of the outlet channel parallel 
 to the weir crest and discharge into it laterally. Another method 
 is to concentrate the length of overflow weir by constructing it in a 
 dentated form, thus reducing the total width of spillway opening. 
 
 A sluiceway for the protection of a canal should in general have 
 a capacity not less than that of the canal so that if necessary the 
 entire flow may be diverted. The bottom of a sluice gate should be 
 some distance below the grade of a canal, in order to increase 
 its capacity and make it more effective in its operation. The 
 gates closing a sluiceway should be of a type easily operated 
 and fitted with the necessary devices to insure their operation when 
 required. 
 
 Culverts. — In connection with canal construction, culverts are 
 used: first to carry drainage water under the canals, and, second, to 
 carry canals under roadways or through embankments where open 
 cuts are not feasible. Whether a culvert be used for carrying water 
 
Plate VI 
 
 *wi^' ■'" 
 
 
 Fig. a. — Series of checks and drops with inclined chutes terminating in water 
 cushion with concrete bloclis to brealc the force of the water. North Platte 
 Project, Nebr. 
 
 Fig. B. — Notched checlc and drop with projecting lip beneath each notch to dif- 
 fuse and break the force of the falling water. Rio Grande Project, N. Mex. 
 
 (Facing Page 80) 
 
Plate VI 
 
 Fig. C. — Concrete chute, built instead of a series of drops, and terminating 
 in a water cushion with concrete baffle board. Boise Project, Idaho. 
 
 
 M 
 
 1^. ..^^ 
 
 tf^-"^. 'rsj....\Mm 
 
 *a!g»^^^^^^ 
 
 -' T^i 
 
 mi— 
 
 <** 
 
 __ ^ W %■ ^ f.,. 
 
 ». .....a^MMM 
 
 T/35 
 
 pp 
 
 
 -: TMI 
 
 
 ^^fe 
 
 BjS 
 
 «IB 
 
 ^^ '" '^y 
 
 ' 
 
 
 "a 
 
 ^^^S^m^^^F 
 
 ^s 
 
 - 
 
 
 J^g 
 
 
 ■^^^^s 
 
 
 
 a ^^^ 
 
 
 s^"^ 
 
 »^r^ 
 
 ^ 
 
 l'^'^,^... 
 
 E 
 
 
 ^;^^^^ 
 
 
 •t^C 
 
 Si^l^^ 
 
 
 
 
 
 Fig. D. — Spillway lip to automatically permit escape of excess water from 
 canal back into river and sluice gates provided to facilitate scouring out of 
 materials deposited in upper portion of canal. Salt River Project, Ariz. 
 
CANAL STRUCTURES 81 
 
 under a canal or whether it be used for carrying the waters of the 
 canal, the general principles of its construction do not differ mate- 
 rially. The principal points to be considered in the design and con- 
 struction of culverts are size or capacity, section, grades, economy 
 and permanency of construction. 
 
 The capacity of a culvert to carry the waters of a canal will be 
 limited to the capacity of the canal. The capacity of a culvert to 
 carry drainage water under a canal was treated under Lateral Drain- 
 age. In this connection, attention is called to the fact that errors in 
 the capacity of drainage culverts are likely to be on the side of mak- 
 ing them too small rather than too large. It is impossible to prove 
 that a culvert is too large but a very simple matter to prove that it is 
 too small should its capacity once be overtaxed. The section of a 
 culvert carrying an irrigation canal is important on account of the 
 grade it may require. In order that no extra grade be consumed by 
 the passage of water through a culvert its cross-section, both as 
 regards shape and area, must be practically the same as that of the 
 canal. If the area of the waterway be contracted so that a higher 
 velocity is required in the culvert than in the canal, additional grade 
 is necessary to produce and maintain the added velocity. If the 
 shape of the waterway is changed additional friction results, which 
 also requires head to overcome. 
 
 On account of the excessive cost, it is not practical in most cases, 
 to construct culverts of the same shape and area of cross-section as 
 the canal of which they form a part. In most cases, economy can be 
 effected both by reducing the area of the cross-section and by building 
 it of such a shape that the minimum amount of material is required for 
 the maximum cross-sectional area. The most economic section, so 
 far as hydraulic properties and amount of material required are con- 
 c«-ned, is the circle. This section is not always practical, however, 
 on account of the abrupt changes which it introduces in the channel. 
 For example, a canal 2.5. ft. deep and having an average width of 
 20 ft. will have practically the same cross-sectional area as a circular 
 culvert whose diameter is 7.3 ft. On account of the necessity of 
 contracting the stream and the lowering of the grade of the culvert 
 far below that of the canal a round culvert is not the most favorable 
 for wide and shallow canals. 
 
 Where a culvert is intended to carry drainage water different con- 
 ditions ordinarily prevail, and the same necessity for conforming the 
 shape of the culvert to the shape of the canal does not exist. In 
 general, however, the. grade of a culvert should not be much below 
 
 6 
 
82 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 the grade of the waterway in order to avoid its being silted partly 
 full and rendered less effective when it is needed. 
 
 The forms of culverts most generally in use are what are commonly 
 designated as "barrel" and "box" culverts, the former being ordi- 
 narily a circle or ellipse and the latter of rectangular form. According 
 to the materials used, culverts may be classified as wood, pipe, and 
 masonry. Wood culverts are commonly constructed in rectangular 
 form and consist of a framework sufficiently strong to carry the em- 
 bankment above, covered with planking which forms the waterway. 
 
 Concrete GoUar 
 
 7 IscfaM Ilikk 
 
 t Elevation) ^ 
 Inlet or C 
 
 Nde : The obunel Kbove ud ImIov tbe culTert ihould lie prsteet«d with gnuUd rip-np 
 or pariof; to the dbtanoe required lij local coDdltioiu. 
 
 G>»Tel 
 
 .alf Section A-B 
 ntlet 
 
 Fig. 26. — Vitrified pipe culvert with concrete inlet and outlet. 
 
 Pipe culverts (Fig. 26) are either vitrified, concrete, iron or steel. 
 Masonry culverts are generally constructed of either stone or 
 concrete. 
 
 The selection of the materials from which a culvert is to be made 
 involves questions of cost, importance, and diurability of the structure. 
 In most sections of the country culverts can be constructed of wood 
 at a less cost than from other materials. On account of the perish- 
 able nature of wood, however, it is not satisfactory for permanent 
 work. For small openings', not exceeding say 4 or 5 ft. in diameter, 
 pipe culverts are satisfactory. Whether or not vitrified, concrete, 
 iron or steel pipe be Used will depend, to a certain extent, upon the 
 relative cost of these materials in the particular locality where they 
 are to be used. Vitrified, or concrete pipe, with joints laid in ce- 
 ment mortar, make a very satisfactory culvert. 
 
 For large openings, say those exceeding 5 or 6 ft. in diameter, 
 culverts should, in most cases, be constructed of solid masonry, 
 either stone or concrete. During the last few years, or since 1905, 
 satisfactory structures of this kind have been made of reinforced 
 
CANAL STRUCTURES 
 
 83 
 
 concrete, the reinforcement permitting the reduction of the thickness 
 of the walls and greatly reducing the quantity of concrete required 
 and corresponding cost of the structure (Fig. 27). 
 
 In the design of all culverts, especial care must be exercised to see 
 that they are of sufficient strength to carry the weight imposed upon 
 them by the embankment above. Another essential, especially in 
 culverts under canals or waterways, is that they shall be water-tight. 
 Seepage along culverts should be guarded against by the construction 
 of ample cut-ofi or curtain walls. Where a culvert is designed to be 
 operated under a head, these cut-off walls should be carried entirely 
 
 
 
 r-—-]\=^—-^^ 
 
 -'^ 
 
 Note-. Grouted 
 Bip-rap or Paving 
 to Suit Local 
 conditions. 
 
 Concrete CollaT 
 for Single Culvert 
 
 T Inches Thick 
 
 Single Culvert 
 
 Double Culvert 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Vertical Section 
 
 Concrete Collar 
 for-Double Culvert 
 
 7 Inchea Ibick 
 
 Elevation of Upper Portal 
 
 Elevation of Lower Portal 
 
 Fig. 27. — Reinforced concrete culvert. 
 
 around the culvert. Approaches to culverts should be protected 
 by wing and curtain walls and the bottom and sides of the channel 
 should be paved. Where there is a material change in the shape of 
 the cross-section from a canal to a culvert such change should be made 
 gradual in order to reduce, so far as possible, the amount of friction 
 and entry head required. 
 
 Flumes. — Where topographic conditions are such as to make ordi- 
 nary canal construction impracticable, flumes are frequently \ised. 
 In general, flumes may be classified as bench and trestle flumes. 
 
 Bench flumes are used on side hill work where the slopes are too 
 steep or the material unsuitable for an open canal. The foundation 
 for such a flume is excavated in the side of the slope and should 
 
84 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 be level transversely and have approximately the same grade as the 
 flume horizontally. The important points to be considered in pre- 
 paring the foundation to receive the flume are : (a) Seciurity against 
 unequal settlement in the foundation; and (b) security against 
 injury to the flume by slides of rock or earth. 
 
 Bench or side hill flumes should be supported upon natural mater- 
 ials when practicable, the excavation being made somewhat wider 
 than the flume. Where, on account of the excess cost of excava- 
 tion, as is sometimes the case on steep, rocky slopes, it is uneconom- 
 ical to excavate into the slope wide enough to receive the flume, the 
 lower edge of the bench should be built up of rock or masonry to 
 make it secure against settlement. As a general rule, flumes should 
 not be supported upon an earthen foundation part in cut and part 
 in embankment, as the embankment portion is almost sure to settle. 
 Foundations for bench flumes, especially if they be of earth, should 
 be carefully drained to care for seepage and storm water carried 
 down over the slopes. The drainage water should be collected along 
 the upper edge of the bench and carried across it at frequent intervals 
 in well-protected channels. Where large waterways are crossed on 
 the slope the flume should be carried over them by means of trestles 
 or suitable spans in order to leave ample waterways below. 
 
 The excavated slopes above the bench should, for the sake of 
 economy, be made as steep as they will safely stand. The degree 
 of steepness will depend partly upon the character of the materials 
 and partly upon climatic conditions. Especial care should be 
 exercised to see that all masses of rock which are partly loose are 
 removed. In choosing the location for a side hill flume care must be 
 exercised to see that the location is a sufficiently safe one that, with 
 reasonable care and attention, the flume can be continuously main- 
 tained and operated. 
 
 Trestle flumes are used for carrying canals across depressions. 
 One of the principal questions to be determined in connection with 
 their use is that of feasibility. This should be determined by care- 
 fully prepared estimates of the various plans by which the work can 
 be accomplished. In making such estimates weight must be given 
 to permanency and cost of future maintenance, as well as to initial 
 cost. For example, a canal constructed in an embankment of suit- 
 able material, even though its first cost exceed that of a flume, might 
 eventually be far cheaper on account of its permanent character and 
 low cost of maintenance. 
 
 Conditions are occasionally so much in favor of a particular kind 
 
CANAL STRUCTURES 
 
 85 
 
 c 
 o 
 •a 
 
 « ggmo 
 f^ Ota &OIB 
 
 a i3 
 
 Vm, 
 
 Jifl- 
 
 h 
 
 W V 
 
 nlMi 
 
 J.mWv|iJ>' 
 
 
 1 
 
 
 1 P 
 
 1 p* 
 
 r 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 HI ■! 1 
 
 1 
 
 
 
 
 
 
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 [l-.-.KSHI 1 1 
 
 
 m ■] 1 
 
 \ 
 
 W 
 
 wp 
 
 vf. 
 
 hvM [^ 
 
 III c 
 
 i ^ 
 
 H 
 
 
 I ' ' ^"' 
 
 pWSAflJW^ 
 
86 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of construction that comparative estimates are hardly necessary, 
 while in other cases careM and detailed estimates are required. 
 Where first costs do not differ materially, preference should be given 
 to the plan which is most permanent in character and requires the 
 least expenditure for maintenance. It is often necessary to consider 
 also the amount of water losses. For a tight flume the losses by 
 seepage and evaporation evidently will be less than from an earthen 
 canal constructed of more or less porous material. For this reason, 
 flumes are sometimes used to reduce seepage and evaporation losses. 
 
 In constructing a trestle flume, the foundation is of prime impor- 
 tance. If a trestle be of wood (Fig. 28) or other perishable material, 
 it should be placed upon masonry carried well up above the surface 
 of the ground. On account of the possibility of the ground under a 
 flume becoming saturated, excessive loadings may cause settlement 
 and should be avoided. Where possible, drainage for foundations 
 should also be provided. In high trestles, wind pressure should be 
 considered and the structure made safe against overturning from 
 this cause. 
 
 The materials in the United States available for flume construction 
 and within reasonable limits of cost are wood, metal, and concrete. 
 Wooden flumes can be built for the lowest first cost in many sections 
 of the arid west where timber is comparatively cheap. On account 
 of the perishable nature of wood, however, the life of a flume of this 
 character is short and maintenance charges, especially after the 
 first few years, correspondingly high. Flumes are usually wet only 
 a portion of the year and the alternate action of water and sun upon 
 lumber has a tendency to warp and crack it, so that it is difficult to 
 maintain a wooden flume in a water-tight condition. For the above 
 reasons wooden flumes are not entirely satisfactory and their con- 
 struction should be avoided if possible. 
 
 A type of flume used quite largely and one which has given satis- 
 faction is a metal waterway supported upon a trestle or foundation 
 of wood. These metal flumes are now manufactured from plates of 
 comparatively pure iron, which it is claimed is less affected by corro- 
 sion than ordinary iron or steel. The accompanying Fig. 29 gives 
 the principal dimensions of one of these metal flumes, supported 
 on wooden trestles and provided at the ends with concrete inlet 
 and outlet. A view of such flume in use is shown in Plate VII, 
 Fig. D. 
 
 Reinforced concrete flumes have been constructed in some local- 
 ities. On account of the lasting qualities of this material it is prob- 
 
CANAL STRUCTURES 
 
 87 
 
88 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 able that the life of such a flume will be many times that of one built 
 from wood or metal. The first cost of concrete flumes is relatively 
 high but their superior lasting qualities and low maintenance costs 
 seem to entitle them to consideration from an economic standpoint. 
 (See Plate VII, Fig. A.) 
 
 In wood and metal flumes the waterway or lining should be so con- 
 structed that it can be replaced without disturbing the main struct- 
 ure. This permits of repairs being readily made to the lining which 
 ordinarily fails first. Various plans have been tried with more or 
 less success for making the joints of wooden flumes water tight. The 
 most common form of joints are caulked, battened and loose splined. 
 Of these it is believed that splines are the most satisfactory in pro- 
 ducing a joint secure against leaks. In a joint of this kind the 
 thickness of the spline should be the same as the width of the groove 
 and the width of spline slightly less than twice the depth of the 
 groove. The latter precaution is necessary to prevent the spline 
 being split when the planks of the lining are driven together. 
 
 Where a flume joins an earthen embankment especial care must be 
 taken to prevent the current cutting around its ends since water has 
 a tendency to follow a joint between earth and a hard or smooth 
 material such as wood or concrete. One of the best methods of 
 preventing this erosion around the ends is to enlarge the ends of the 
 flume for a distance of 15 or 20 ft. and carry the earthen embankment 
 into these enlarged ends. That portion of the flume into which' the 
 earth filler is carried should have its floor depressed to a depth of 
 2 or 3 ft. below the grade of the canal and its side walls carried well 
 out into the center of the canal embankments. A curtain wall 
 should also be carried down at the ends of the flume (see Fig. 29). 
 The bottom and slopes of the canal for some distance from the ends 
 of a flume should be protected by means of rock or other form of 
 paving. This paving, if constructed with rough surface, tends to 
 check the velocity of flow along the sides and bottom of the canal 
 and reduces the chances of erosion. 
 
 Velocity and Flow of Water in Flumes. — In order to reduce the 
 size of a flume to a minimum, the velocity of flow in it should exceed 
 that in the canal. Flumes are generally of material that will stand 
 high velocities without danger of erosion; the velocities which may 
 be attained in them are usually, however, limited by the grades 
 available and the checking of the flow at the lower end of the flume 
 rather than by the velocity which the material will stand. 
 
 The velocity of flow in a flume may be computed from the slope, 
 
Plate VII 
 
 Fig. a. — Concrete flume carrying water of main canal across side drainage lines. 
 North Platte Project, Wyo.-Nebr. 
 
 Fig. B. — Concrete inverted siphon carrying water of main canal under side 
 drainage line instead of over it. North Platte Project, Wyo.-Nebr. 
 
 (Facing Page 88) 
 
Plate VII 
 
 Fig. C. — Concrete pressure pipe used in place of flume. Sun River 
 Project, Mont. 
 
 uT''- 
 
 
 _ ^ * w> 
 
 ^^^^(*«tS^-«-#^4\s^^^ 
 
 
 
 
 
 
 
 
 
 ' 
 
 
 "- 
 
 
 ^^feta^ 
 
 
 r.. 
 
 t. -^ 
 
 j^^^^ '*» 
 
 4, ^ .., ^ 
 
 ,'•<"'*- 
 
 %^- -„ - 
 
 
 ! 
 
 
 jr^l 
 
 ^ 
 
 ♦•^♦•t-m^S 
 
 K 
 
 
 s 
 
 
 E 
 
 
 
 » 
 
 
 S 
 
 1 
 
 
 1 
 
 
 1 
 
 ^ 
 
 
 ill 
 
 Fig. D. — Metal flume on timber trestle. 
 
CANAL STRUCTURES 89 
 
 hydraulic mean radius, and an assumed value of "n," the same as 
 for open canals. Where the velocity in a flume exceeds that in the 
 canal above there must be sufficient drop at the upper end of the 
 flume to provide for entry and increased velocity heads. The 
 value of the entry head will depend upon the form of transition 
 curves from the canal to the flume section and may ordinarily in 
 practice be made so small as to be negligible. The increased velocity 
 head is the head corresponding to the velocity in the flume, less 
 the head corresponding to the velocity in the canal above. Calling 
 
 Its value h it may be obtained from the expression h = ^ 
 
 where Vi equals velocity of flow in the flume, Fa equals velocity in 
 the canal above and g equals the acceleration of gravity in feet per 
 second. At the lower end of a flume, where the velocity is reduced 
 to that of the canal, there is a slight gain in head due to the water 
 giving up a part of its kinetic energy. Theoretically it is possible 
 to regain the greater part of this increased velocity head when the 
 velocity is reduced; practically, however, it is not possible to regain 
 but a small amount of it. 
 
 On account of the resistance of change in direction, flumes intended 
 to carry water at reasonably high velocities should be free from 
 sharp turns or reduction in grades. If these be introduced there 
 is a tendency for the water to pile up at the point of change and 
 possibly overflow the sides of the flume. 
 
 Tunnels. — A tunnel in connection with irrigation works is that 
 portion of a canal or outlet of a reservoir which passes underground 
 or pierces projecting ridges. The tunnels on the main-line canals 
 are necessitated by the fact that, especially near the heads of the 
 canals where they leave the river, the ground is frequently very 
 rough and open cuts are difficult if not impossible to construct and 
 maintain. Under these conditions, the most economical form of 
 construction is to continue the canal by suitable excavations into 
 and through the solid rock or partly consolidated earth, holding 
 this in place if necessary by temporary timbering to be replaced 
 later by permanent lining. In several instances tunnels of con- 
 siderable length have been built through a mountain range or 
 plateau to bring water from a distant river. The most notable of 
 such tunnels is that on the Uncompahgre Valley project in Colo- 
 rado over 30,000 ft. long taking the entire summer flow of Gunnison 
 River and the tunnel of the Strawberry Valley project, Utah, over 
 22,000 ft. long, the other dimensions of which are given in Fig. 30. 
 
90 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 This takes the water stored in Strawberry Valley through the top 
 of the Wasatch range. 
 
 In planning tunnels not only should the first cost be considered, 
 but more than this the expense of future maintenance of such tunnel 
 as compared with an open cut. The latter, especially on steep 
 hill sides, is exposed to many dangers; either it may slide out as a 
 whole aided by the weight of the water and by the softening of the 
 material, or it may be filled, in whole or part, by earth and rock 
 sliding in from above. Thus the construction of a tunnel is often 
 justified even though the first cost is larger than that of an open cut. 
 
 Experience in operating and maintaining finished canals is 
 
 Portal Sets 
 
 nltli 
 
 Transverse Sills 
 
 I o/ CJflf I If 'I 
 
 >, r — ' r* — i^ i B Cup 
 
 ^2 Lagging 
 
 Inside Sets 
 
 with 
 
 Longitudinal Sills 
 
 Detail of Loneitudinal Sill 
 
 and 
 
 Post Connection 
 
 5U1 &«t in Bottom 
 
 Fig. 30. — Concrete lined tunnel, Strawberry Valley Project, Utah. 
 
 demonstrating that as a rule a considerable portion of the canal 
 which has been built in very rough ground might have been more 
 economically placed in tunnel, because the latter when once properly 
 constructed is relatively permanent. The tendency is therefore 
 to construct canals more and more in tunnel than in the past and 
 in case of doubt in poor locations to throw the conduit underground 
 rather than attempt to keep it wholly on the surface. 
 Tunnels may be built of the full size and capacity of the canal 
 
CANAL STRUCTURES 91 
 
 or for economy of construction, the cross-section may be reduced. 
 In the latter case, it is obvious that the velocity through the tunnel 
 must be increased by giving it additional grade and the approach 
 to the tunnel must be so designed as to provide sufficient velocity 
 of entrance to permit water to the entire capacity of the canal to 
 pass through the tunnel. This latter feature has been neglected 
 on some notable works and the tunnels when finished have been 
 found to obstruct the flow so greatly as to necessitate expensive 
 changes. 
 
 The decrease of the section of the tunnel and consequent increase 
 in slope results in the canal descending somewhat rapidly and thus 
 losing the advantage of elevation in commanding irrigable land. 
 If the descent of the ground from the intake of the canal to the 
 irrigable land is so great that there is ample grade allowable without 
 sacrificing irrigable area, then it follows that heavy grades can 
 be given to the tunnel and corresponding reduction of cross-section. 
 But if, on the other hand, the area of irrigable land is limited by the 
 elevation to which the water can be delivered, then it may be 
 necessary to keep the size of the tunnel, to the full area of cross- 
 section of the canal thus reducing the slope and keeping the canal 
 at the highest practicable elevation. These balancing considerations 
 should be taken into account in all designs of canals where tunnels 
 are used. 
 
 The construction of tunnels may be considered as almost a 
 distinct branch of engineering, especially those in soft ground 
 where great skill must be employed in holding the roof and walls. 
 For the present purpose, it is sufficient to call attention to the fact 
 that in all tunnel work there necessarily exist great uncertainties 
 as to the conditions to be encountered and the probable time and 
 cost of completion. As part of the preliminary survey and examina- 
 tion, borings should be made at short intervals along the proposed 
 route and all possible facts obtained as guidance in preparing pre- 
 liminary estimates and plans and specifications. Even with the 
 most thorough exploration by drill holes and other methods such 
 as are feasible under the circumstances, there are still considerable 
 risks to be run and a large contingent expense must be allowed. 
 
 Lining. — Lining must usually be provided for tunnels of this char- 
 acter not only to prevent the top and sides from falling in but also 
 to reduce the friction and increase the capacity of the tunnel by 
 providing smooth walls. It is usually necessary to set timbers to 
 hold the roof and in many instances it is not safe to remove these 
 
92 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 timbers; thus they are left in place being embedded in the permanent 
 concrete lining. In extreme instances, it has been found necessary 
 to use iron plates bolted together to hold the soft materials from 
 falling into the tunnel and in these cases also this temporary lining 
 is not removed but is covered by the concrete. 
 
 Where the walls and roof are of solid rock with no apparent tend- 
 ency to disintegrate the tunnel is usually excavated as nearly as 
 possible to the prescribed dimensions or neat Unes and finished up 
 to the true dimensions by a relatively thin lining of concrete, the 
 voids between the concrete and the rock being filled with small stone. 
 For this purpose, forms of wood or of metal are provided and are 
 drawn through the tunnel on suitable tracks or other devices, being 
 taken out and advanced as rapidly as the concrete sets. 
 
 Where the lining will be subject to heavy pressures the thickness 
 is increased and all spaces filled in with concrete or stones embedded 
 in it. It is highly desirable to preserve a smooth finish and to have 
 the interior of the tunnel free from roughness which will tend to 
 check the velocity of the water. 
 
 Inverted Siphons. — ^An inverted siphon or "siphon" as it is more 
 frequently termed, is used for conducting water across depressions 
 or under streams. It consists of a water-tight pipe or conduit usually 
 laid below the surface of the ground and through which water is 
 carried by gravity. Siphons take the place of trestle flumes in 
 crossing depressions or streams. The question as to which method 
 of construction is most feasible depends for answer upon local condi- 
 tions in each particular case. (See Plate VII, Fig. B.) 
 
 The accompanying Fig. 31 gives the principal dimensions of one 
 of the similar reinforced concrete siphons for carr)dng a distributing 
 canal under a roadway on the North Platte project in Nebraska. 
 
 Siphons are better adapted to the crossing of deep ravines or 
 canyons than flumes on account of the impracticability and cost of 
 constructing and maintaining high trestles. They are also better 
 adapted to carrying a canal across a stream of varying depth since 
 they permit the water in the canal being carried at any elevation, 
 while if carried by a flume it must be kept above the high-water 
 elevation of the stream. In general, siphons are susceptible of more 
 permanent construction and require less expense for operation and 
 maintenance than trestle flumes. 
 
 In the design of a siphon it is necessary first to determine the 
 amount of pressure or head to which it will be subjected, the fall 
 available in its length and the character of the material in which it 
 
CANAL STRUCTURES 
 
 93 
 
 ( I M 1 1 1 1 1 1 Trn- 
 
 iinniiMiiii iYrr[Vi'i'iMii)iiii/iii);i 
 
 T 
 
 hifZ-^ I 
 
 
 ii;mii(|ii||(.iiiii;iiiiiii"i'h 
 
 I. Ml I 
 
 
 rmrmii 
 
 Ah 
 
 
 
 a 
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 XI 
 
 a 
 
 P< 
 
 -jL 
 
94 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 is to be constructed. The first two are necessary to arrive at the 
 strength and size of conduit to be used and can be determined from 
 a profile of the line. A knowledge of the character of material is 
 necessary to enable the selection of proper foundations and anchor- 
 ages for holding the conduit in place, and should be obtained by 
 careful field examinations and excavations if necessary. 
 
 The head on any point of a siphon is the distance from that point, 
 measured vertically, to the hydraulic gradient between the intake 
 and outlet of the siphon. If this distance be expressed in feet the 
 pressure ^ in pounds per square foot is p = ()2.^h. If the diameter 
 of the pipe is d, the transverse stress, s, in pounds acting upon 
 I lineal foot of the wall of the pipe and tending to rupture it is 
 
 s=t2.ih— From this the strength of pipe or conduit required 
 
 is readily computed. 
 
 The available head tending to overcome friction and produce flow 
 in the pipe is the difference in elevation between the water surfaces 
 at the two ends of the pipe. The head per unit length of pipe is 
 this difference in elevation divided by the length of the pipe. From 
 this the velocity of flow can be computed by the ordinary formulae 
 for the flow of water in pipes, allowance being made for velocity and 
 entrance head. In order to obtain the maximum capacity of a 
 siphon there should be a depth of water in the canal or entry chamber 
 over the entrance to the pipe equal to the sum of the velocity and 
 entry heads. Or the upper end of the pipe may be made of larger 
 sections than the remaining portion. 
 
 The foundation under a siphon should be sufficient to insure safety 
 against settlement under the combined load of the siphon and the 
 water which it carries. It should be firmly anchored in place in 
 order to prevent disturbances which would have a tendency to cause 
 leaks, and if laid under a stream it should be well below the shifting 
 bed of the stream. The depth to which a siphon should be placed 
 below the surface of the ground outside of the stream bed or whether 
 or not it should be covered at all will depend upon local conditions. 
 A covering of earth, if made heavy enough, will prevent freezing 
 during extreme cold weather and tends also to minimize the changes 
 in temperature throughout the year and thus reduce contraction and 
 expansion. Where siphons of concrete or metal, which have an 
 appreciable coefficient of expansion are subjected to considerable 
 changes in temperature, they should be provided with expansion 
 joints at frequent intervals. All siphons, where possible, should 
 
CANAL STRUCTURES 95 
 
 be provided with means for emptying them for purposes of examina- 
 tion and repairs when necessary. 
 
 The materials from which siphons are commonly constructed are 
 wood, steel, or iron, and masonry, including plain and reinforced 
 concrete. 
 
 Wooden siphons are commonly constructed in the form of wood 
 stave pipe, the necessary strength to resist the pressure imposed upon 
 them being given by iron or steel bands. The size and spacing of these 
 bands are dependent upon the size of pipe and the amount of head 
 upon it. Siphons of wood stave pipe are being operated under heads 
 of loo ft. or more. On account of the wood staves being saturated 
 with water they are not subject to decay to any marked degree, so 
 that the life of such a siphon is practically the life of the metal bands. 
 Siphons of steel or wrought iron may be used under any desirable 
 heads, cost being practically the only limit. For extreme heads, say 
 from 20D ft. upward, these materials, on account of their high tensile 
 strength, seem to be the most practicable. In using steel or iron pipes 
 it is customary to cover them with some form of coating, such as coal 
 tar or asphaltum compounds in order to protect them from corrosion. 
 A siphon recently constructed by the United States Reclamation 
 Service on the Uncompahgre Valley Project, Colorado, is made of 
 practically pure iron. This siphon is approximately 3,700 ft. in 
 length, 26 in. in diameter, and is subjected to a maximum head of 
 about 200 ft. Pure iron was used upon the theory that this material 
 wiU better withstand the corrosive action of certain alkali salts con- 
 tained in the soil in which the pipe is laid. 
 
 Masonry siphons, except when reinforced, arf practicable for low 
 heads only. Reinforced concrete siphons have been constructed and 
 are being successfully operated under heads up to about 100 ft. In 
 constructing reinforced concrete siphons especial care must be taken 
 to make a dense, non-porous concrete, in order to prevent leakage. 
 Additional water-tightness can also be obtained by plastering the 
 interior of the pipe with a rich mortar of cement and sand. Suf- 
 ficient steel reinforcement must be used to withstand the entire water 
 pressure with a reasonable factor of safety. 
 
 A combination of tunnel and siphon is occasionally necessary 
 in connection with large irrigation works. One of the most notable 
 examples of this kind is the tunnel under Colorado River near the 
 town of Yuma, Arizona, where the main line of the irrigating canal 
 is taken out on the California side, flows southerly to a point opposite 
 Yuma, and then is carried under the river by means of a tunnel, water 
 
96 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 rising on the Arizona side, and continuing in the main line, with 
 slight loss of head. There thus results a tunnel under pressure which 
 is in effect an inverted siphon shown in Fig. 32. 
 
 This tunnel was driven through partly indurated sands beneath 
 the bed of the river by the use of compressed air; it is nearly 1,000 
 ft. in length and 14 ft. in side diameter. Similar less expensive 
 tunnels are occasionally necessary in passing under the beds of 
 streams, but as a rule these are built in the arid regions dxiring 
 the time of year when the streams are dry, or the flow is so small 
 that it can be carried in a flume across the point of construction 
 
 Oalifomia 
 
 Sana j: 
 OoancGnrel 
 
 700 600 500 400 300 
 
 Distances ftom California Shaft 
 
 Fig. 32. — Vertical section of siphon or tunnel under Colorado River, Yuma 
 
 Project, Arizona. 
 
 and the tunnel built in the open. Still smaller structures which 
 can hardly be termed tunnels are frequently built to permit the 
 passage of canals under a depressed railroad track, or in other 
 localities where it is not practicable to carry the water on grade. 
 
 Bridges. — Where canals are constructed across public or private 
 roads, so as to interfere with ordinary transportation, bridges must 
 be provided. Whether or not these structures are built by public or 
 private interests, or by the owners of a canal system, are matters of 
 detail which may vary in individual cases. It must be recognized, 
 however, that they are necessary and sooner or later must be con- 
 
CANAL STRUCTURES 97 
 
 structed. By whomsoever built, provisions should be made that a 
 type of bridge be adopted that will not interfere with the operation 
 and maintenance of the canals. In order to accomplish this in a satis- 
 factory manner the designer of a canal system should also provide, or 
 at least approve, the plans for bridges which may be constructed 
 across it. 
 
 Aside from the general appearance of a bridge, which is an item 
 worthy of consideration in a prosperous community, the principal 
 point for consideration is that they shall not interfere with the flow 
 of water in the canal. To insure this they must be constructed well 
 above the maximum high-water surface. A safe rule to follow in 
 this is to make the height of the bottom of the floor system above 
 the maximum water surface equal to the free board of the canal. 
 On large main canals, where bridges of considerable lengths are re- 
 quired, the question whether piers or center bents may be constructed 
 in the canal or whether a clear span should be used depends upon local 
 conditions. If a canal carries large quantities of silt or debris, any 
 obstruction is likely to prove a menace to the free flow of water. 
 Floating weeds, such as are found in many sections of the west, are 
 especially dangerous and may obstruct the channel to such an extent 
 that water will be forced over its banks. Where the water is clear 
 and does not carry floating materials, center bents may be used 
 without detrimental effects. 
 
 The kind of bridge to be used, whether wood, steel, or concrete, 
 will depend upon the permanency of the structure required and the 
 relative costs of the various materials in the particular locality. In 
 the design of bridges consideration should be given to the maximum 
 loads which they may be required to carry. This will depend upon 
 the nature of the traflSc and will vary in different sections. The 
 maximum load on a public highway bridge should not exceed one- 
 fourth or one-fifth of the ultimate strength of the bridge. All 
 crossings over canals should be constructed in a manner not to inter- 
 fere with free access along the canal. 
 
 Measuring Devices. — The amount of water diverted from the 
 source of supply to the canals and also the amounts delivered from 
 the canals for irrigation or other purposes, should be determined 
 for the proper management of the system. The quantity drawn 
 from a source of supply must be known in order to determine what 
 is available for use and to properly conserve this supply. The 
 various amounts diverted from the canal system must be known 
 in order to ascertain how much is being delivered to water users 
 
98 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 under the canal and how much is lost or wasted. Whether water 
 be disposed of at a unit price for a given quantity say an acre-foot, 
 or whether it is paid for in terms of the area irrigated, a knowledge 
 of the quantities delivered is essential. 
 
 In order to determine the amount of water diverted to and from 
 a canal system each diversion structure should be provided with 
 some means of ascertaining the amount of water which it delivers. 
 In this connection it is well to state at the outset that water measure- 
 ments under the conditions that exist in practical irrigation are 
 liable to serious inaccuracies and that improvement in this particular 
 branch of irrigation work is urgently needed. The inaccuracies of 
 our present methods, however, do not justify their neglect nor 
 discontinuance. 
 
 In general, measuring devices for use on canals may be brought 
 under four classes; namely, submerged orifices, weirs, rating flumes, 
 and mechanical meters. The factors involved in the use of sub- 
 merged orifices are the size of the orifice and the head upon it. 
 Where a constant head can be maintained fairly accurate results 
 can be obtained, the difficulty, however, is to maintain this constant 
 head. This method of measurement is commonly used to determine 
 the amount of water passing large headgates, the quantity of dis- 
 charge, Q, being computed from the formula Q=AC\/2gh. Where 
 A is the area of opening, g the acceleration of gravity in feet per 
 second, h the head, and C a constant depending upon the shape of 
 the opening. Submerged orifices are also sometimes used to de- 
 termine the amount of water diverted into small canals, the head 
 being determined by taking the difference in elevation of the water 
 surfaces above and below the orifice by means of fixed gages. This 
 form of apparatus has the advantage of not requiring any consider- 
 able amount of fall and can be used where it is necessary to hold 
 up' the water surface in order to cover the maximum area of land. 
 Where low heads are used the results computed from head and 
 area of opening are subject to considerable error. 
 
 One of the most convenient and accurate methods of determining 
 the discharge into a small canal is by means of a weir. The depth 
 of water flowing over a weir can be shown with reasonable accuracy 
 by means of a gage and from the gage reading the quantity flowing 
 can be readily determined. One objection to the use of weirs is 
 that they require a loss of head from the main canal to the lateral 
 equal to approximately the depth of water flowing over the weir. 
 In exceptionally flat countries a drop of a few inches in the lateral 
 
CANAL STRUCTURES 99 
 
 may mean the loss of a considerable amount of land. For this 
 reason it is not always practicable to install weirs at the head of 
 laterals. 
 
 Weirs must be kept in good repair in order to obtain reliable 
 results. The required conditions as to fall and contraction of the 
 channel must be maintained, this usually requiring frequent atten- 
 tion. The smaller weirs are rapidly obstructed by silt, the bottom 
 is built up and the end contractions are partly suppressed. Fre- 
 quently the smaller canals or laterals below the weirs become choked, 
 backing the water up on the crest of the weir. Continuous attention 
 is required on the part of a well-trained force of canal men to keep 
 these in proper condition. 
 
 A less accurate, but more simple method of measuring the flow 
 is by means of a rating flume placed in the canal, whose waters are 
 to be measured, a short distance below the head. This flume may 
 be of either wood or concrete and its depth should be sufficient to 
 carry the desired quantity of water. Its width is ordinarily about 
 the same as that of the canal. The capacities of the flume for 
 different depths of water are determined by calibration, that is, 
 by measuring the discharges at various depths by means of a weir 
 or current meter. Flumes, like submerged orifices, require but 
 little head for their operation, and for this reason can be used where 
 weirs are not applicable. 
 
 One of the chief objections to any of the above measuring devices 
 is that no account is taken of changes in flow due to variations in 
 the head of the canal. In order that these variations be shown it is 
 necessary that they be equipped with self-recording water-stage 
 registers, which, for a large canal system, are expensive, both to 
 install and to maintain. 
 
 Mechanical meters consist of some form of revolving wheel which 
 is operated by the current and whose velocity of rotation varies 
 with the velocity of flow. The apparatus is placed in a contracted 
 section of the canal, built of wood or masonry. The revolutions 
 of the wheel are graduated in terms of the quantity of water dis- 
 charged, either in second-feet or acre-feet. 
 
 A form of self-measuring apparatus now being tried on some of 
 the projects of the United States Reclamation Service registers the 
 amount of water delivered in acre-feet. 
 
 In the use of the various forms of water-measuring devices much 
 depends upon the ability, judgment, and skill of the persons using 
 them. The essential thing in constructing a canal system is that 
 
100 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 some form of measuring device should be installed. The type 
 selected for any canal system should be that best suited to the con- 
 ditions which prevail on that particular system. 
 
 Screens. — It is necessary to screen the inlets to all pipes and 
 culverts to prevent floating material being carried into them, and 
 to exclude fish at the head of canals taking water from perennial 
 streams. In the United States it is usually required by state law 
 that fish screens be installed. The western states as a rule require 
 that the bars of these screens be not more than 1/2 in. apart. This 
 results in catching floating leaves, sticks, grass, and moss so that 
 the screens are quickly clogged and the canal banks may be flooded 
 unless the screens are watched constantly, or some automatic device 
 is provided. 
 
 Screens should consist of nearly vertical bars without any cross 
 bars near the surface which can catch the teeth of a rake or other 
 tool used for cleaning. The most successftil screen so far known is 
 that consisting of iron bars 1/2 in. wide and 2 in. deep, arranged as a 
 grill, inclined at an angle of one in four, and with a footway near 
 the top from which the operator can work. 
 
 Protection of Canal Structures. — On account of the important 
 functions of canal structures and the magnitude of the damage which 
 may result from their failure, especial care should be taken for their 
 protection. The principal causes of failure which must be guarded 
 against are erosion and seepage. These causes are common to 
 practically aU classes of structures which are used for controlling 
 or regulating the flow of water. The general principles applying to 
 one case are, therefore, equally applicable to another. 
 
 Where the section of a waterway or canal is changed or where the 
 velocity of flow is increased, one or both of which may occur at head- 
 gates, checks, drops, and diversion structures, there is a tendency 
 to set up eddy currents or disturbances which may cause erosion of 
 the sides or bottoms of the channel. This erosion may take place 
 either above or below a structure and cause a dangerous condition 
 to exist before it is discovered. To avoid this source of damages it 
 is necessary first to so design structures that the variations from the 
 normal canal section will be a minimum, and second to thoroughly 
 protect the channel above and below them. 
 
 When water is carried over a drop an increase in the velocity of 
 flow cannot be avoided. This increased velocity must be reduced 
 at the bottom of the drop and the channel at that point must be 
 sufficiently protected to absorb without danger the energy expended 
 
CANAL STRUCTURES 101 
 
 upon it. The same is true of water carried through turnouts under 
 any considerable head, and it is necessary to guard against erosion 
 at the points of entrance and discharge of these structures. A very 
 satisfactory form of channel protection is rough stone paving laid 
 on a firm foundation and the joints filled with concrete mortar. 
 The advantage of rough stone is that it checks the velocity more 
 effectively than a smooth paving. 
 
 Seepage along the sides and under structures should be guarded 
 against by the use of ample cutoff walls, and by backfilling around 
 all structures with impermeable material carefully puddled or tamped 
 into place. The construction of projecting rings or collars on a turn- 
 out pipe will, to a large degree, prevent seepage water following 
 along the outside of the pipe. Thin narrow buttress walls, carried 
 up along the outside of a structure, will reduce the tendency of seep- 
 age water to follow around the structure. Embankments above 
 structures, especially where wing walls are carried into them, in 
 addition to being carefully constructed should be made of generous 
 dimensions. 
 
CHAPTER VI 
 DISTRIBUTION SYSTEMS 
 
 Canals and Laterals. — The term "Canal Systems" applied to 
 irrigation works includes all channels used in conveying water from 
 the source of supply to the point where it is ultimately delivered 
 onto the land. The channels included in a canal system may vary 
 greatly in dimensions and have capacities ranging from above i,ooo 
 cu. ft. per second down to i cu. ft. per second or less. The various 
 conduits or a canal system are usually classified under the general 
 heads of canals, laterals or distributaries as the latter are sometimes 
 called. The distinction between canals and laterals is, to a certain 
 degree, an arbitrary one. In general, however, the term canal is 
 applied to a channel which carries water for irrigation but from which 
 direct diversion of water onto the land is not made. The term lateral 
 is applied to a channel which takes water from the side of the canal 
 and carries it along or near the canal and out onto the land to be 
 irrigated. 
 
 Canals are further sub-divided into main and branch canals. A 
 main canal is one which carries water directly from the source of 
 supply. Branch canals, as the name implies, are those which carry 
 water from a main to different irrigable areas. Laterals are also sub- 
 divided into main and branch laterals. The terms more frequently 
 used, however, in this connection, are laterals and sub-laterals; a 
 lateral being a channel which, in addition to distributing water from 
 a canal directly to the lands, also conveys it to smaller branch or 
 sub-laterals. The term "Distribution System" is intended to in- 
 clude channels which carry water from canals and distribute it onto 
 the lands. 
 
 It is to be noted that the definition of canals and laterals takes no 
 account of the relative capacities of these channels. A channel 
 defined as a lateral may, therefore, have several times the capacity of 
 another channel properly defined as a canal, i.e., the main canal of a 
 system taking water from a stream or reservoir to 10,000 acres may 
 be smaller than the lateral of another system supplying 20,000 acres, 
 or more. 
 
 102 
 
DISTRIBUTION SYSTEMS 103 
 
 General Plan of Distribution System. — The requirement of a 
 distribution system is that it shall be capable of supplying water to 
 all irrigable lands under the canals. In general, irrigable lands are 
 divided into small areas or individual holdings, and an adequate 
 distribution system is assumed to be capable of delivering water to 
 the highest point of each of these small areas. The plan of a dis- 
 tribution system will depend upon the topographic features of the 
 tract to be irrigated, and, in general, each system must be modified to 
 suit peculiar conditions. 
 
 For irrigation requirements lands may be considered under three 
 classes: (a) uniformly sloping planes, (b) ridges, (c) undulating areas, 
 portions of which are higher than any other lands immediately 
 adjacent to them. The problems met in planning a distribution 
 system are those of reaching each of the above-described areas with 
 a minimum amount of construction work. 
 
 Uniformly sloping planes allow great latitude of design in distribu- 
 tion canals and permit ordinarily the laying out of rectangular or 
 parallel systems of laterals. Where possible these laterals should be 
 located along land sub-divisions and property lines. This plan of 
 location avoids the necessity of cutting across individual farms by 
 canals and frequently reduces the amount of good land otherwise 
 required for right-of-way for canals. Systems of this kind should 
 have the laterals or sub-laterals near enough together so that water 
 can be carried over the lands from one farm to the next adjacent to it. 
 Where topographic conditions are favorable, the area between two 
 laterals may be covered partly from one side and partly from the 
 other. 
 
 Ridges must be reached by laterals constructed along their highest 
 portions. These laterals must necessarily conform to the direction 
 of the ridges so that water may be carried from either side down the 
 slopes to the intervening depressions. This necessitates an appar- 
 ently irregular plan, the laterals crossing the fields. 
 
 Undulating areas are by far the most difl&cult to irrigate and no 
 general plan is applicable for different cases. High spots above the 
 level of adjacent lands may be reached by means of ditches or flumes 
 built above the surface of the ground. Siphons or pressure pipes are 
 also used to carry water across low depressions to the higher lands. 
 The choice of one of the various plans which may be used for reach- 
 ing isolated high areas ordinarily requires comparative studies of 
 cost as well as consideration of their relative merits for permanency 
 and efficiency. 
 
104 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 The necessity of a carefully considered plan of works for the dis- 
 tribution of water cannot be too strongly insisted upon. The dis- 
 tribution system is to an irrigation project what a delivery system is 
 to a transportation company in carrying on its business. If a dis- 
 tribution system fails or is inefficient, the entire irrigation system fails 
 or is rendered inefficient to a greater or less degree. Mistakes made 
 in the original planning and laying out of a lateral system ordinarily 
 cannot be corrected without damage to improvements and a corre- 
 sponding high cost for making changes. The ultimate value of an 
 irrigation system depends upon its efficiency in supplying the needs 
 of the water user. 
 
 Topographic Surveys for Lateral Systems. — On small areas, or 
 areas the topography of which is comparatively simple, the most 
 feasible plan for a lateral system can ordinarily be determined with- 
 out extensive topographic surveys, the method followed being to 
 determine the elevation of the commanding points on the area and 
 using these as a basis for the location of the main laterals. In 
 making these preliminary studies the principal point to be considered 
 is to locate the main laterals so that they will command as much as 
 possible of the irrigable area. In preparing plans in this manner 
 alternate surveys should be freely made in order that all possible 
 and feasible plans may be considered. 
 
 For large areas, or areas where the topography is complex, contour 
 maps should be prepared as a basis for laying out lateral systems. 
 The principal objection to a topographic survey for this purpose is its 
 cost. One of the first points which must be decided is whether or not 
 the topography is such that the advantages to be gained in the effi- 
 ciency of the system are sufficient to justify the expense of such 
 surveys. The advantages of topographic surveys as a basis for plan- 
 ning lateral systems are as follows: (a) They show the general slopes 
 of the country, give at once the amount of fall which is available, and 
 serve as a guide for the general direction in which laterals should be 
 constructed, (b) On complex topography, such as broken ridges or 
 isolated high areas, they indicate what lands can be covered by 
 surface canal and those which must be reached by means of flumes 
 or siphons, (c) Several alternate systems of laterals can be laid 
 out on a carefully prepared contour map and preliminary estimates 
 made thereon, at a much less cost than these studies can be carried 
 on in the field, and the individual areas into which a tract must 
 be broken in order to reach all points can be readily determined, 
 (d) Topographic surveys, in addition to being an aid in the designing 
 
DISTRIBUTION SYSTEMS 105 
 
 and locating of a lateral system, are of benefit in future maintenance 
 as they indicate, in a general way, how irrigation can best be carried 
 on after the system has been constructed. 
 
 Where the topography is such as to permit of various plans being 
 used the cost of a topographic survey of the lands to be covered is 
 justified, and, in most cases, there is an actual saving by this pro- 
 cedure, due to the more economic method in which engineering 
 studies can be made and the greater efl&ciency of the system that can 
 be designed. In working from topographic maps the engineer has 
 before him, in condensed form, the entire irrigable areas and is thus 
 enabled to project thereon all possible plans. In working directly 
 from the ground, it is impossible, especially if the topography is com- 
 plex, to see all of the various methods which may be used and some 
 of the most advantageous features of a design may be overlooked. 
 
 Topographic maps to be used for designing a lateral system 
 should be constructed on a sufficiently large scale to enable the 
 various works to be projected thereon. The contour interval 
 should be small enough to enable one to determine from the map, 
 to within a reasonable degree of accuracy, the courses of the various 
 laterals, the location of drops and other structures, as well as the 
 areas which can be brought under any particular lateral. The 
 scale and contour interval best adapted to a particular case will 
 depend upon the nature of the country, the most complex topog- 
 raphy requiring the smaller contour interval and larger scale. In 
 general, maps to be used for lateral locations should have a contour 
 interval not exceeding i ft., and a scale ranging from 400 to 1,000 
 ft. per inch. 
 
 Where contour maps are prepared for aid in designing a lateral 
 system, attention should be given to other features which will 
 make them valuable for future use in connection with operation 
 and maintenance work. The contours should be projected upon 
 an accurate base map, which should show, in so far as they can be 
 located, the positions of all public and private land lines and corners. 
 
 Capacity of Laterals. — The discussion of capacity of canals, 
 given on page 39, applies also to laterals and distributaries. In 
 the design of the smaller distribution canals, however, some factors 
 must be given consideration which are insignificant and may be 
 omitted for larger canals. One of these already mentioned is that 
 of the maximum duty of a canal. A canal which is used only a 
 portion of the time, as is commonly the case with a small lateral, 
 must have a greater capacity per unit area of land covered by it 
 
106 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 than one which is operated continuously. Other and equally 
 important factors in small laterals are evaporation and seepage 
 losses. 
 
 Evaporation losses from small bodies of water, climatic con- 
 ditions being practically the same, will vary almost directly as the 
 area of water surface. The percentage lost from a small canal on 
 account of its less depth will exceed that from a large canal. Evapo- 
 ration losses from the direct water surface in canals are, however, 
 relatively small compared with seepage losses. The proportion 
 of water lost by seepage is also much greater in small than in large 
 canals. The results of observation on this subject, while not con- 
 clusive, seem to show that the average seepage losses from canals 
 carrying more than loo cu. ft. per second is less than i per cent, 
 per mUe of canal, while for canals carrying less than lo cu. ft. per 
 second the average losses exceed lo per cent, per mile. On account 
 of the higher seepage losses the allowance made for them in fixing 
 the capacity of a small lateral must be relatively much greater 
 than for a large canal. Just what these losses will amount to in 
 any particular case will depend upon the character of the material 
 forming the waterway of the canal. It must be remembered, 
 however, that seepage losses are constantly taking place from 
 earthen canals and that whUe the percentage of loss may be so small 
 as to be negligible in very large canals it may be sufficient to materi- 
 ally effect the capacity of a small lateral. 
 
 Some investigations have been made to determine seepage losses 
 in terms of the wetted area. These results show losses varying 
 from about 0.25 to 6.0 cu. ft. of water per square foot of wetted area 
 per day. In most cases, however, the daily rate of seepage varies 
 from about 0.5 to 1.5 cu. ft. per square foot of wetted area. Data 
 on see page losses, in this form, are the most convenient for practical 
 use in determining comparative losses in various materials. They 
 can readily be reduced to a percentage of total flow per mile for 
 any particular size and shape of canal. 
 
 An illustration showing the method of taking account of seepage 
 losses may be of interest. Let it be required to deliver at the lower 
 end of a lateral 10 miles long, water at the rate of 20 cu. ft. per 
 second. Assume the seepage losses to be 3 per cent, per rmle. 
 How much water must be supplied to the head of the lateral? 
 The safe and quick method of ccmputing this would be: multiply 
 the percentage of less per mile by the length of canal in miles, 
 which gives a total loss of 30 per cent. This result is slightly in 
 
DISTRIBUTION SYSTEMS 107 
 
 excess of the actual theoretical losses, since no account has been 
 taken of reduced amounts being carried at each succeeding mile. 
 The actual amount reaching the lower end of the lateral, computed 
 upon the basis of 3 per cent, of that delivered to it being lost in 
 each mile, is 0.97'°=. 737 or 73.7 per cent, approximately. The 
 quantity which must be delivered to the head of the lateral to 
 supply 20 cu. ft. per second at its lower end is 20 divided by .737 
 = 27.1 cu. ft. per second. 
 
 The minimum amount of water by which irrigation can be effec- 
 tively and economically carried on is sometimes called an irrigation 
 head. It will vary for different kinds of soil and crops. In general, 
 however, it may be said to range from i to 10 second-feet. 
 
 The capacity of a lateral, whatever the area under it may be, must 
 be large enough to carry enough irrigation heads or sufl&cient water 
 to permit of economic irrigation. In order to carry on irrigation 
 economically and to get over the ground satisfactorily, sufiicient 
 water must be supplied to permit of a cultivated area or field between 
 checks or ridges being entirely covered before that portion to which 
 water is turned first becomes unduly saturated. 
 
 The growth of grass and Tweeds in laterals tends to materially 
 reduce their capacity and should be taken into account when design- 
 ing a distribution system. This reduction, while small in sectional 
 area, in some cases may be sufficient to reduce the velocity and 
 consequent capacity of a canal by as much as 40 or 50 per cent., 
 thus rendering it too small to carry an effective irrigation head. 
 
 Location of Laterals. — The problems involved in the location of 
 small laterals differs in some respects materially from those met in 
 the location of larger canals. The principal function of a main or 
 branch canal is to carry water from the source of supply to the 
 smaller distributaries or laterals. The importance of main and 
 branch canals as a part of a system demands that they be given the 
 safest possible location which the nature of the country and reason- 
 able limits of costs wUl allow. Since water is ordinarily not diverted 
 from these canals directly to the lands it is unnecessary to carry 
 them above the surface of the ground in order to reach especially 
 favorable points for diversion. 
 
 The function of a distributary or lateral is to carry water directly 
 to the irrigable lands. The location must be so chosen that the 
 maximum area can be watered. Favorable points for diversion 
 must also be considered and the laterals brought to them. The 
 general elevation of laterals must be sufficiently high to enable the 
 
108 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 water surface to be kept above the adjacent lands. Where necessary 
 in order to accomplish this the waterways of laterals must be con- 
 structed in embankment. In other words, the main object to be 
 considered in lateral location is the delivery of water to the greatest 
 possible area. 
 
 Safety against breaks in laterals should be insured by properly 
 planned and constructed banks, rather than by reducing the amount 
 of land under them to obtain a more favorable location. It is 
 frequently necessary to compare the difference in the cost of con- 
 struction over two different locations with the value of extra land 
 which can be reached if the more difl&cult route be chosen. In 
 making such comparisons it must be remembered that the value of 
 lands, when once brought under irrigation, may be expected to con- 
 tinue to increase in value, and for this reason the greatest develop- 
 ment possible should be considered. 
 
 On uniformly sloping areas, all of which can be watered by two 
 or more systems of laterals, eflEiciency of system and economy of 
 construction should be considered. These questions may involve 
 the laying out of alternate systems and the making of estimates 
 on each. On flat slopes, where the velocities are necessarily low 
 there is usually an economy in serving as much land as possible from 
 a single lateral, on account of the larger cross-section required and 
 correspondingly higher velocities which may be attained. 
 
 Cross-section of Laterals. — In fixing the cross-section of a lateral 
 there should be considered (a) the character of the material; (b) the 
 method by which it is to be excavated, and (c) the grade or slope. 
 
 Lateral ditches are for the most part constructed in fertile soils 
 which will not support steep banks. Ordinarily it is not practicable 
 to construct slopes steeper than i to i, and, except in very rare cases, 
 is it necessary to make them flatter than 2 to i. If laterals are built 
 by means of teams and scrapers, slopes of i 1/2 or 2 horizontal to 
 I vertical are the most practicable from the standpoint of con- 
 struction, since these slopes facilitate team work in taking out the 
 excavation. If, on the other hand, the work is to be done by 
 excavating machinery, slopes as steep as i to i may be found to 
 an advantage. In permeable soils, where seepage losses are high, 
 as steep slopes as possible should be used in order to reduce the 
 amount of wetted area to a minimum. 
 
 The ratio of bottom width to the depth of water is an important 
 factor in determining the velocity of flow. Where the land is nearly 
 level and it is necessary to conserve grade as much as possible, a 
 
DISTRIBUTION SYSTEMS 109 
 
 comparatively narrow and deep section is the most advantageous. 
 Where the fall of the land is considerable and it is necessary to reduce 
 velocities, much can be accomplished by adopting a wide and 
 shallow section. In fixing the ratio of width to depth, account 
 should be taken of the method by which excavation is to be carried 
 on and also the character of the material for resisting seepage. 
 
 The top width of banks and their height above the water surface 
 will depend upon the stability of the material of which they are 
 constructed, and the degree of safety against overtopping which it 
 may seem desirable to adopt. In general, the top width of banks, for 
 the smaller laterals, need not exceed about 3 ft. The height above 
 the water surface should be sufficient to give stability to the embank- 
 ment and serve as a protection against overtopping in case of a 
 sudden rise in the canal. It is not an uncommon occurrence for a 
 lateral, especially a small one, to be required to carry temporarily 
 an overload of 50 per cent, above its figured capacity and provisions 
 should be made for such emergencies. Where the waterway is all, 
 or a great part, in fill, a greater height of free board should be allowed 
 than where it is in cut. This latter precaution is necessary to give 
 stability and provide for settlement in the higher embankments. 
 
 Points of Delivery of Water. — The location of points where water 
 is to be delivered from laterals and sub-laterals to the lands will be 
 determined to a great extent by the topography of the lands to be 
 irrigated. The fundamental requirement is that these points be so 
 located that water can be carried from them over the maximum area 
 by means of small farm ditches. The number of delivery points 
 should be as small as possible and still provide ample means for 
 reaching the entire irrigable area. By reducing the number of delivery 
 points to the minimum required, the cost of construction, operation 
 and maintenance of small diversion structures is reduced. In gen- 
 eral, delivery points should be located on the highest lands possible, 
 or in other words, where the laterals or sub-laterals are entirely or 
 to a large extent in excavation. These higher points are as a rule 
 more favorable for delivery of water to the lands and also for the safe 
 maintenance of structures. 
 
 A condition which frequently arises to increase the number of de- 
 livery points of a lateral is that where the irrigable area is divided into 
 small individual holdings, each requiring an independent water outlet. 
 Such a system permits the amount of water turned to each user to be 
 measured and controlled and prevents the necessity of water users 
 making distribution of water among themselves. Delivery of water 
 
110 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 direct to each user, especially where lands are held in small tracts of 
 from lo to 20 acres, requires a much more elaborate and costly dis- 
 tribution system than where one deliveiy point can be made to serve 
 an area of from 40 to 80 acres, or more. 
 
 The numbei of delivery points required depends upon the topog- 
 raphy of the lands to be irrigated, the size of individual land hold- 
 ings and the policy to be pursued in the delivery of water, that is, 
 whether it is to be delivered to each individual or to associations of 
 water users. 
 
 The question cf fixing delivery points of a distribution system is 
 one which requires careful study and considc ration in each individual 
 case, the fundamental principles to be worked out in these studies 
 being to reduce the number of delivery points to the fewest prac- 
 ticable and stiU provide an efficient service for the entire irrigable 
 acreage. 
 
 Delivery Box.^The term " Delivery Box " is usually applied to the 
 structure which regulates and controls the distribution of water from 
 the lateral to the land of the farmer. It is the last link in the system 
 of canals and distributaries which carries water from the source of 
 supply to the area upon which it is to be used. The requirements of 
 a delivery box are that it be adequate to control and measure the 
 water which passes it, and that its capacity be sufficient to deb'ver 
 the maximum amount of water required for irrigating the lands under 
 it. Various types of boxes are used in different irrigation syFtems 
 and special forms are frequently devised to meet certain conditions. 
 It is impossible to say that any one type is superior to all others. A 
 fundamental principle which should be borne in mind is that delivery 
 boxes are essentially a part of a canal system and should therefore be 
 opened and closed only by the organization which operates the canal 
 system. They should be so constructed that should it be found 
 necessary, interference with them by unauthorized persons can be 
 detected and prevented. 
 
 The amount of water delivered to the lands can be measured only 
 at the point of deliveiy. It is therefore necessary that a delivery 
 box be provided with suitable equipment for ascertaining the water 
 which passes through it, if record of the amount used in irrigation is to 
 be kept, as it should be in every case. 
 
 The simplest form of delivery box consists of a rectangular wooden 
 structure placed in the side or bank of a canal or lateral and provided 
 with an opening through which water is diverted. When not in use, 
 the opening is closed by means of boards or some simple form of gate 
 
Pr.ATE Vlir 
 
 
 
 Fig. a. — Distributing laterals with wooden boxes and gates, typical of the 
 pioneer work in irrigation. Yakima Project, Wash. 
 
 Fig. B. — Concrete box and drop on distributory in place of earlier form of 
 wooden construction. Orland Project, Cal. 
 
 {Facing Page no) 
 
Plate VIII 
 
 Fig. C. — Cast-iron valves on distributing systems instead of the usual wooden 
 gates. Uncompahgre Project, Colo. 
 
 ^ 
 
 
 (■18^^^^'"^-?'*' '''*''''*? ^-"''"*-.»~i"»*^ *• ^ ,-^<'^'-^ /"^s^SH 
 
 ., , ; "'''■■ 
 
 "^ 
 
 
 I^^H^^^^^^^1mB9HIIII^H 
 
 
 
 
 ■■"'■"'■Y'^l^ 
 
 ^H^^^^ 
 
 - ■--''':.■■' ''^ -''"'■' ^ '/U--^''t''^ 
 
 
 ;^^^^?^^t|,.^**"' " ., .•.„£„ " ' 
 
 Fig. D. — Farmers' water gates on inclined concrete slabs. Sun River 
 Project, Mont. 
 
DISTRIBUTION SYSTEMS 
 
 111 
 
 which can be raised to the required height to pass the quantity of 
 water desired. More permanent structures of the same type are 
 constructed of concrete or other form of masonry, and the openings 
 closed by means of metal gates. Another type consists of a covered 
 box of wood or masonry carried through the banks and having the 
 upper and lower ends protected so as to prevent erosion. (See 
 Plate VIII.) 
 
 The forms of measuring devices commonly used are weirs, rating 
 flumes and some type of submerged orifice through which the flow 
 
 Fig. 2:^. — Plank measuring box with Cippoletti weir and automatic register. 
 
 of water can be determined. Where there is suf&cient fall to permit 
 its being used, the weir is perhaps the most satisfactory, cheap and 
 simple device for measuring relatively small flows, such as are com- 
 monly turned into farm ditches and the smaller laterals and sub- 
 laterals. For this purpose both the rectangular and Cippoletti weirs 
 are used (Fig. 33). The latter type of weir possesses some advan- 
 tage over the former as it is unnecessary to take account of end 
 contractions. 
 
 A rating flume ordinarily consists of a square or rectangular box 
 open at both ends and placed in the channel so as to form the water- 
 way for a distance of several feet. The flume is first rated for 
 
112 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 various depths of water flowing through it by means of current depths 
 of water flowing through it by means of current meters, weirs or other 
 suitable measuring devices. For convenience of reference, the 
 amount of discharge for different depths are commonly shown by 
 means of a graphic curve or table. Measurements are then made by 
 observing the depths of water passing the flume and taking the corre- 
 sponding discharge from the curve or table. 
 
 A submerged orifice consists of an o'pening through which water is 
 allowed to flow under a small pressure or head. The amount of 
 head, if the orifice has a free discharge, is found by taking the height 
 of water above its center, or if the lower side of the orifice be sub- 
 merged, by taking the difference in elevation of water above and 
 below the orifice. The amount of discharge depends upon the head, 
 size of orifice and the form of the upper edge of the opening, whether 
 square or round. The quantity of discharge Q may be computed 
 from the expression Q= ACy/ gh where A is the area of orifice, C 
 a constant depending upon the form of the upper edge of the opening, 
 g the acceleration of gravity in feet per second, h the head in 
 feet. In order to determine accurately the amount of water passing 
 a submerged orifice, the value of C for that particular form must 
 be previously determined. Roughly, this value may be said to vary 
 from about 0.6 as a minimum to i.o as an ultimate maximum. For 
 a more complete determination of the flow of water through orifices, 
 the reader is referred to special works on hydraulics. 
 
 Automatic devices for the measurement of water have been used to 
 a small extent. They consist essentially of submerged orifices each 
 provided with a current meter for measuring the velocity. These 
 devices are commonly so graduated as to indicate the actual amount 
 of water passed in some convenient unit of measurement, such for 
 example as the acre-feet. In all measuring devices, unless they are 
 provided with automatic registers, serious errors are apt to occur on 
 account of variable heads, frequently found in the laterals. These 
 errors in a great measure can be overcome for weirs, rating flumes and 
 submerged orifices by the use of water-stage registers which show at 
 all times the head in the canal. 
 
 The expense of refined measxu"ing apparatus is usually large and 
 it is frequently a question whether this is justifiable. The reply 
 depends almost wholly on the value of water in the particular 
 locality where they are to be used. For this reason in determin- 
 ing the type of measuring device, it is necessary to take the value of 
 the water into consideration. In this connection, it should be borne 
 
DISTRIBUTION SYSTEMS 113 
 
 in mind that water for irrigation is becoming constantly more and 
 more valuable, and that while at the present time it is delivered 
 through inefficient measuring devices, it is probable that within a few 
 years, on account of the increased demands for water for irrigation 
 purposes and its correspondingly increased value, careful measure- 
 ments will be required. It is being more and more appreciated that 
 in order to properly regulate the amount of water placed upon lands 
 fairly accurate measurements of the quantity used must be kept. 
 Wherever possible, therefore, as accurate means of measuring as are 
 consistent with the conditions at hand should be provided. 
 
 Flumes and Pipe Distributaries. — In many irrigated sections 
 flumes and pipes are commonly used instead of earthen channels for 
 the smaller distributaries. The principal advantage of a flume or 
 pipe over an earthen canal is the saving of water. They are also 
 sometimes used on rough or undulating areas to avoid fills and cuts 
 which would be necessary in constructing the small earthen channels. 
 In very pervious materials, such, for exiample, as sand and gravel, it 
 is impossible to carry a small quantity of water for any considerable 
 distance in an earthen canal on account of the rapid absorption of 
 water by the soil. 
 
 The Smaller the quantity of water carried, in pervious materials, 
 the greater is the relative effect of losses and the shorter the distance 
 which water may be delivered. For example, in a channel carrying 
 50 or 100 second-feet, seepage losses which may amount to i 
 or 2 second-feet per mile may be neglected, since they represent but 
 a small percentage of the quantity of water carried. If, however, 
 a channel carrying but i or 2 second-feet has the same rate of loss 
 per square foot of wetted area in its channel, the entire quanity is 
 soon absorbed. 
 
 Flume or pipe distributaries not only facilitate the flow of water 
 and make irrigation possible on lands where it woiild otherwise be 
 practically impossible, but they also result in large savings of water. 
 These savings are sufficient in many cases to justify a large original 
 outlay for their construction. Pipes, as a rule, are much more 
 satisfactory than flumes, especially in warm climates where it is not 
 necessary to protect them from freezing, either by careful drainage 
 during the winter or by burying them to a sufficient depth below the 
 frost line. 
 
 Wooden flumes are frequently used to cross low depressions, 
 especially in the northern lands where lumber is relatively cheap. 
 Wooden pipes are also sometimes used for this same purpose. These 
 
114 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 pipes are laid so as to act as inverted siphons under a small 
 head. 
 
 Cement pipes are commonly used for distributaries in the inten- 
 sively cultivated sections of southern California where the water 
 supply is limited and where it is necessary to conserve it to the high- 
 est possible degree. These pipes are laid to a sufficient depth to 
 insure their protection against the cultivation of the soil and are 
 provided with frequent taps carried up to the surface from which 
 water is discharged. They are constructed sufficiently strong to 
 carry low heads and serve as pressure pipes where necessary to carry 
 water across slight depressions in the ground. With a distribution 
 system of this kind, little if any water need be wasted since it can be 
 distributed from the pipes only at such points as required. 
 
 Accessibility to Laterals. — Id designing and laying out a distribu- 
 tion system provisions must be made for easy access to all parts 
 thereof. It must be borne in mind that even for the smallest canals 
 which form a part of a system for the delivery of w ater they must be 
 patrolled and operated almost daily. It is consequently of the 
 greatest importance that the person in charge of operation and main- 
 tenance of these canals be unhampered in his efforts to reach them 
 for this purpose. In order to properly maintain laterals, it is 
 necessary that materials can be delivered to them quickly if necessary. 
 In the event of banks being broken or washed away, earth for the 
 repairs of the same is necessary, and provisions must be made for 
 obtaining this material without delay. 
 
 The remarks heretofore made relative to rights-of-way for canal 
 apply equally well to the smaller distribution canals, and no canal, 
 however small, which is to form an integral part of a system and for 
 which the owners of such system are responsible for its maintenance, 
 should be constructed except on rights-of-way under their control. 
 It matters not whether these rights-of-way be actually owned by an 
 irrigation company or whether the right-of-way for the canal is 
 simply in the form of an easement, the main question is that no one 
 shall have any right to dispute the authority of the operators to 
 enter on the right-of-way and operate and maintain canals in a proper 
 manner. 
 
 Canal systems are built for the benefit and use of persons engaged 
 in tilling the soU, and it is essential that these persons be unhampered 
 in their farming operations by undue restrictions on access to their 
 canals. This is especially true on small distribution canals which 
 must of necessity cross irrigable lands. The cooperation of both 
 
DISTRIBUTION SYSTEMS 115 
 
 the water users and the company or firm delivering the water is 
 necessary. In order that this cooperation shall be effective, con- 
 cessions must frequently be made by both parties, and any agree- 
 ments for rights-of-way should be made specific enough to fully 
 define the rights of each. 
 
 Conditions frequently arise where a small distribution canal must 
 be constructed across private holdings in order to supply water to 
 the lands of others. Such a canal is often a detriment to the person 
 whose lands it crosses and may be unnecessary for his individual use. 
 In such cases, it is absolutely necessary that no opportunity be given 
 to this owner, should he be so inclined, to interfere with the delivery 
 of water to the irrigators below. Right-of-way agreements in such 
 a case should be so specific that it is not left to one individual to say 
 whether or not his neighbor shall receive water. 
 
 The amount of right-of-way which wUl be required in individual 
 cases, will, of course, depend upon local conditions. It is essential, 
 however, that in every case there be suflB.cient to permit the canals 
 to be operated and allow repairs to be made promptly when neces- 
 sary. In general, it may be said that the rights of the people under 
 a distribution system are paramount to the rights of any one indi- 
 vidual, since it is only upon this basis that an irrigation system can be 
 made a success. In other words, the individual cannct be allowed to 
 retard the work of others on account of inconveniences to himself. 
 
 On the other hand, the individual, where land is crossed by a canal 
 or lateral, is entitled to the protection in his rights and conveniences 
 consistent with the rights of the people as a whole under canals. 
 For example, the individual whose land is thus traversed is unques- 
 tionably entitled to bridge crossings which will give him free access 
 to his land. Provisions must also be made for these crossings 
 being maintained in such a manner that they will not interfere with 
 the operation of the canal. The person or company responsible 
 for the operation of the canal system must have access to all parts 
 of that system. Such right of access, however, should not give 
 them the right to unnecessarily inconvenience adjacent land owners. 
 
 It is impossible to lay down any hard or fixed rules as to exactly 
 what should be acquired in the way of rights-of-way. Each 
 particular case must be given due consideration Ln the planning of 
 a distributon system and rights-of-way acquired so as to fully 
 protect the interests of the individual whose lands are crossed, and 
 also provide for the carrying on of operation and maintenance work 
 in such manner as to make the system fully effective. 
 
CHAPTER VII 
 IRRIGATION BY PUMPING 
 
 General Conditions. — It frequently becomes necessary for the 
 engineer to consider the practicability of supplying water for irriga- 
 tion by pumping. Conditions of this kind may be the result of the 
 lands being situated at a higher elevation than any available water 
 supply, thus making irrigation by gravity impossible, or it may be 
 that the distance from a gravity supply is too great or the character 
 of the country such as to make the building of canals impracticable. 
 
 The general principles involved in pumping for irrigation are not 
 unlike those involved in pumping for municipal and domestic uses. 
 Concerning the latter there are many data available which may 
 have general application to pumping for irrigation. It must be 
 recognized, however, that the quantity of water required for irriga- 
 tion ordinarily greatly exceeds that needed for a municipal and do- 
 mestic supply. Another important point to be considered is the 
 value of water for irrigation purposes compared to what it is worth 
 for the use of a town or city. A price which may be considered 
 reasonable and which the residents of a town can well afford to pay 
 for domestic use may be excessive when considered in connection 
 with agricultural operations. This is because of the fact that the 
 amount of water required for irrigation, considered with reference 
 to cost, is excessive when compared with that necessary for all pur- 
 poses in cities of moderate size. 
 
 The pumping equipment which would be weU within the financial 
 means of a city covering a thousand acres would be no more than 
 adequate for a farm of the same extent. The return in revenue, 
 however, between these two areas, one covered by business blocks 
 and residences, is many times that which would be received from 
 profits derived from the sale of crops grown on an equal extent of 
 land. 
 
 Thus a pumping plant which might be of relatively low cost when 
 considered for the city, is out of the question for the country. 
 
 The fundamental differences which must be considered in study- 
 ing successful pumping plants installed for municipal purposes and 
 in adopting similar plants for agricultural purposes lie in the follow- 
 ing facts: 
 
 116 
 
IRRIGA TION BY F UMFING 1 1 7 
 
 For city purposes a relatively small quantity of water is required 
 to be lifted to a considerable height, in many cases 200 ft. or more, 
 while for ordinary irrigation purposes 70 ft. is at present near the 
 maximum. The quantity of water for city purposes is expressed 
 in gallons per minute; that for agricultural purposes in cubic feet 
 per second, i cu. ft. per second equaling 449 gal. per minute. The 
 total quantity pumped is expressed for city purposes in millions of 
 gallons; for agricultural purposes in acre-feet; i acre-foot equaling 
 325,850 gallons, or about a third of a million gallons; and one million 
 gallons equaling 3.07 acre-feet. 
 
 The cost of raising water for a city may be as high as $20 to $30 
 per million gallons, or about $6 to $10 per acre-foot, while for ordi- 
 nary field crops a fair cost would be 50 cents per acre-foot, and 
 a large cost $1 per acre-foot. 
 
 For city purposes the supply must be practically continuous day 
 and night, increasing during the extreme heat of the summer when 
 water is used for irrigating lawns and gardens or similar small areas. 
 Thus the men and machinery are kept continuously employed. 
 
 For agricultural purposes a supply is ordinarily required for a few 
 months only during the irrigation season. Even during this period 
 the amount required is by no means constant. For a short time 
 during the early heat of summer the demand is large, but drops off 
 rapidly as cooler weather approaches. Thus it happens that men 
 and machinery employed in pumping for irrigation are idle for a 
 large part of the time unless some secondary employment can be 
 found for them. 
 
 Source of Supply. — A well of some form may be considered 
 as the typical source of supply of water pumped for agriculture. 
 Conditions may arise where it is possible to pump water from a 
 flowing stream. As a rule such stream is of large size and has such 
 gentle slopes that it cannot be diverted by gravity, otherwise pumps 
 would not be used. Under some conditions water may be pumped 
 from a lake or possibly from a canal. It is usually desirable, how- 
 ever, even in the case of a river or lake, to provide some form of 
 forebay, which is practically a well built on the side of a stream 
 or lake and connected with it so that the water in the well rises 
 or falls with the fluctuations in the river or lake. Wells of this 
 character, fluctuating within a narrow range, present fewer prob- 
 lems than the ordinary form of dug or driven well since the water 
 in the former usually fluctuate less in height and thus offer fewer 
 problems in the design cf economical machinery. 
 
118 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 Having determined that the available source of water supply 
 must be utilized by pumping, the next condition to be considered is 
 the fluctuation in the height of water and the variation in amount, 
 these being usually interrelated. If the source is a large stream 
 or lake, the questions connected with quantity become insignificant 
 and those of the amount of rise and fall of water surface are of 
 more importance. In the case of ordinary wells in earth, however, 
 the question of quantity or rate of deUvery to the well become 
 paramount, controlling as it does not only the height of water in the 
 well, but the size and other conditions of the machinery to be used. 
 
 Observations of the height and fluctuation of the source of water 
 carried on through several months or years are essential in preparing 
 designs for a pumping plant. Every possible information as to 
 the hydrographic conditions should be studied. If it is a matter 
 of general knowledge that the lake or river under consideration 
 has fluctuated within a certain range for many years these questions 
 may be considered as settled. In the case of ordinary dug or drilled 
 weUs, however, the question of quantity of water is far more difficult 
 of solution. Frequently it is impossible to give such wells a thorough 
 test in advance because the cost of erecting testing devices — con- 
 sisting of machinery of sufficient capacity to thoroughly exhaust 
 the wells — may be practically as expensive as to bufld the final 
 plant. The only tests which have real value are those which are 
 made through days, weeks or months to determine as thoroughly 
 as possible all local conditions of rate of flow to the well, for this 
 purpose drawing down the stored water accumulated in the strata 
 in the immediate vicinity. 
 
 There are many popular faUacies concerning the amount of 
 water under ground, especially as regards the "inexhaustible" ' 
 supply. The use of the word "inexhaustible" in this connection 
 usually implies that with the ordinary hand pump or similar devices 
 it has not been possible to appreciably lower the surface of the 
 ground water. Another term which has come into general use in 
 the west, especially in the region of the Great Plains, and which 
 conveys erroneous impressions, is the word "underflow." There 
 is, it is true, an underflow but the rate of this is exceedingly slow, 
 and a more descriptive term would be "percolation." The word 
 "flow" in the minds of most people is connected with the behavior 
 of a river moving at a rate perceptible to the eye, such as a mile 
 or two an hour. The "underflow," if it can be said to flow at all, 
 moves at the rate of from i to 5 ft. a day, or possibly at a slightly 
 
IKRIGA TION BY P UMPING 1 1 9 
 
 more rapid rate when in coarse sand or gravel. The assumption 
 occasionally made in popular literature that there is under ground 
 a great river moving steadily forward and carrying more water 
 than there is in sight on the surface is a fanciful rather than an 
 actual condition. In western Kansas, for example, it is popularly 
 stated that the Arkansas River carries more water underground 
 out of sight than in the visible surface channel. A little reflection 
 will show that this cannot be true. 
 
 Careful tests have been made to show the existence of this under- 
 flow and to secure measurements of the rate and direction of move- 
 ment. This is done by putting down a series of wells in lines or 
 groups and impregnating the waters of one of these wells with 
 ordinary table salt or some other soluble material, the presence of 
 which can be detected by electric or mechanical devices. It has 
 been discovered that there is a definite forward movement of the 
 waters percolating through the sands and gravels which underlie 
 the Valley of the Arkansas River, and that the surface configuration 
 does not necessarily indicate the size or extent of these deeper beds 
 in which water is progressing southerly or southeasterly in a diagonal 
 line across the present river channel. 
 
 These beds of pervious material are very large and their cross- 
 sectional area is probably many times greater than the cross-section 
 of the surface streani, but the extremely slow rate of movement 
 of a few feet a day as compared with 2 or 3 ft. per second on the 
 surface, results in there being a relatively small amount of water 
 per annum carried through these sand and gravel beds. 
 
 There is little doubt that the ground water is reinforced to a 
 certain extent by this slow, gradual percolation, especially through 
 widely spread sands and gravels, but this rate of flow is rarely suffi- 
 cient to maintain the water table at the original height in any country 
 where wells have been in use to a notable extent. McGee' has pointed 
 out that in all settled parts of the United States there has been a 
 decided lowering of the water table, especially where the ordinary 
 dug wells have been supplemented by a large number of the cheaper 
 and deeper drilled or driven wells. He has also shown that in spite 
 of wet years the water table does not return permanently to its former 
 height. If this is true for regions where the demand for -water from 
 underground is limited chiefly to domestic supply or for the watering 
 of cattle, the effect must be more marked where considerable num- 
 bers of wells are provided for irrigation of the surface, as the amount 
 
 1 Wells and Subsoil Waters, by W. S. McGee, U. S. Dept. Agriculture, Bureau of Soils, 
 Bulletin No. 92. 
 
120 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of water pumped from these for agriculture greatly exceeds that 
 which is needed for domestic purposes. 
 
 In constructing a well where the ground waters are apparently 
 abundant, it is desirable to sink a caisson from the surface into the 
 water plane as far as it can be driven, using a pump having a capacity 
 twice that of the pump finally installed. When this is done, it is 
 usual to drUl in the bottom of this caisson two or more of the so- 
 called California wells and connect suction pipes to the pump 
 extending down into these driven wells. Normally these pumps will 
 draw water from the wells and from the bottom of the caisson in 
 which they terminate. If the water plane is drawn down it will then 
 be possible to secure water from the wells even if the bottom of the 
 caisson becomes dry. If the pump loses its suction from any cause 
 the water plane will rise until the pump is submerged and again 
 put in operation. As an alternative method, but one which is not 
 usually to be recommended, is that of driving small tunnels to 
 connect wells situated outside the caisson. A well made by sinking 
 a caisson to some distance below the surface of the underground 
 waters, and having its depth stiU further increased by drilled weUs 
 in the bottom of the caisson, is considered the most permanent form 
 of construction that can be adopted. 
 
 Character of Pumps. — The pumps first used in irrigation were 
 naturally those which previously had been found successful for 
 pumping town supplies, namely, those with plungers or pistons. 
 They fall into two classes — first, those placed horizontally with 
 suction lift and requiring a certain amount of horizontal space for 
 installation, and second, the vertical acting pumps usually so small 
 in horizontal diameter that they can be inserted directly into the well 
 and are thus frequently submerged, attaining, as a rule, greater effi- 
 ciency because of this condition. These pumps were all of the re- 
 ciprocating type, not well suited for economically delivering large 
 quantities of water such as are required in irrigation. They have 
 for this reason been supplemented in modern practice by centrifugal 
 pumps of the single-stage type for moderately low heads and the mul- 
 tiple-stage type for high heads. 
 
 A form of centrifugal pump largely used and operated by electrical 
 power for irrigation is one in which the pump and motor driving 
 it are mounted on the same vertical shaft, frequently they are ar- 
 ranged in such way that the pump and motor can be raised and low- 
 ered as a unit. It is not practicable to mount the motor immediately 
 above the pump because the fluctuations of water in the well are 
 
IRRIGATION BY PUMPING 121 
 
 usually so great that the motor would be in danger of being sub- 
 merged and thus injured. It is necessary, therefore, that the verti- 
 cal shaft be of sufficient length to permit submergence of the pump 
 and at the same time keep the motor well above the water level. 
 This is accomplished by providing a light, steel frame on the upper 
 end of which is carried the motor, and on the lower end the pump, 
 the connecting shaft being supported by the frame at intermediate 
 points so that the whole device forms a stiff but relatively light unit, 
 which can be hung or supported in a well and, if necessary, adjusted 
 to different heights to suit the elevation of water in the well. 
 
 The pump frame may be of galvanized structural steel, or iron, 
 or of wood, and be suspended from beams placed across the top of 
 the casing of the well, the internal diameter of which should be 
 ample to permit insertion of the discharge pipe and the raising and 
 lowering of the pump as shown in Fig. 34. 
 
 The pump is usually placed at a depth of from 30 to 50 ft. below 
 the surface of the ground and a discharge pipe is carried up vertically 
 to the surface independent of the frame. The adjustment is made 
 so as to submerge the pump in such a position that the water surface 
 may rise 15 or 20 ft. or more above the pump and fall possibly 
 10 or 15 ft. below it. 
 
 The capacity of centrifugal pumps arranged for irrigation should 
 be selected to suit the varying conditions of head and available 
 water supply. In this manner a high degree of efficiency can be 
 obtained under all conditions, with the simplest form of automatic- 
 ally operated constant-speed apparatus. The maximum head 
 which is practicable for the ordinary single-stage centrifugal pump 
 is about 60 ft. Multiple-stage pumps may be used for any head 
 desired. A modified form of the multi-stage centrifugal pump 
 known as the deepwell turbine pump may be assembled in two 
 or more units of such dimensions that the pump with its discharge 
 pipe and self-contained shaft can be installed in a driven well casing 
 and driven by either a belt or motor. 
 
 Power for Pumping. — Nearly every kind of power from the strength 
 of animals, probably the earliest form, to the most modern hydro- 
 electrical systems of development and transmission, has been used 
 for pumping water for irrigation. At the present day it is not 
 necessary to consider the use of animal power, although in a few 
 instances under pioneer conditions or for testing the supply, vari- 
 ous forms of machinery operated by horses may be temporarily 
 employed. 
 
122 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 /oC-ogoO- 
 
 & 
 
 wsmk 
 
 
 l^fllCJOOOoC 
 
 o°SS^::: 
 
 
 m 
 
 f'sn 
 
 W 
 
 I n 
 
 'ki 
 
 
 
 Fig. 34. — Vertical section of concrete lined well shaft, with electrically driven 
 centrifugal pump, Salt River Project, Arizona. 
 
IRRIGATION BY PUMPING 123 
 
 Windmills. — Next in order historically, and naturally to the 
 strength of men and animals, comes the use of wind. This is still 
 quite largely employed for irrigating small tracts of ground. (See 
 U. S. G. S. Water Supply Papers No. i, 8, 20, 29, 41, and 42.) 
 Windmills have been improved during recent years, adapted to 
 various purposes and are now a commercial article readily obtainable 
 through agricultural implement dealers. In considering the use 
 of wind as a source of power, it is necessary mainly to secure a good 
 commercial mill, using certain precautions, however, in estimating 
 the actual available power, due allowance being made for assump- 
 tions based on ideal conditions. 
 
 It is usually necessary to supplement any form of wind -mill 
 pump with adequate water storage because of the fact that the 
 amount of water hfted is relatively very small, and with the uncer- 
 tainty of the wind, this small stream of water coming at irregular 
 intervals will soak into the ground before it can be beneficially 
 used in irrigation. The necessity of 3 storage tank arises from the 
 fact that in order to carry the water rapidly and effectively over 
 the ground, it is necessary to have a considerable volume or head, 
 such that the water will pass over or across porous soils so rapidly 
 that no very considerable portion can be lost in transit. (See Plate 
 IX, Figs. A and B.) 
 
 The cost of irrigation by windmiUs is generally prohibitory 
 excepting for intensively cultivated market gardens. It is rarely 
 possible to irrigate more than one-half or three-fourths of an acre 
 with a windmill, unless the mill is unusually large, and the lift 
 very low. The cost for irrigation including construction of well, 
 purchase of windmill, pump, construction of tank, and accessories, 
 may amount to from $100 to $500 an acre. The cost of maintenance 
 is correspondingly large, as all forms of windmill require frequent 
 attention and more or less repairs. The deterioration also is usually 
 quite heavy so that the annual maintenance cost of the equipment 
 rarely falls below $10 or $20 per acre, if allowance is made for the 
 time spent in keeping the apparatus in order. 
 
 Steam Power. — One of the commonly applied forms of power 
 for pumping is steam generated by burning coal or sometimes oil 
 in the ordinary steam boilers, utilizing the force of the steam in 
 reciprocating engines which drive suitable pumps by means of 
 belt or gear connections or by direct piston connection. When 
 used in irrigation the apparatus is sometimes an adaptation of 
 the steam pumps used for town supply. Where the crops are very 
 
124 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 valuable, as in the case of sugar-cane in the Hawaiian Islands, 
 steam pumps are used with success in agriculture, raising water 
 loo or more feet in height, the extreme limit being estimated at 
 about 550 ft. The acreage cost for installation is, of course, 
 exceedingly high, over $100 an acre at the minimum, and the annual 
 maintenance and operation cost for high lifts may run from $30 
 to $50 per acre. The cost is thus prohibitory for ordinary crops, 
 unless some unusual conditions exist. 
 
 Steam turbines have been employed in place of reciprocating 
 engines, these being connected, as a rule, to electrical generators, 
 which in turn operate motors to drive the pumps. A relatively 
 high degree of efficiency has thus been secured and the size and 
 consequent cost of installation has been notably reduced below that 
 of the pther devices. Especially is this true where a large quantity 
 is to be pumped, and where several pumping units can be supplied 
 with power from one central station. 
 
 Gasoline and Oil. — ^A steam plant for pumping water for irrigation 
 necessitates, for fuel economy, large investment and the irrigation of 
 considerable areas, more extensive usually than can be handled by 
 an individual. There has thus arisen a demand for small individual 
 pumping plants to irrigate from 40 to 80 acres, or more. For this 
 purpose the ordinary gasoline or gas engines have been found very 
 effective. Such engines may be considered as replacing or supple- 
 menting the windmill. They permit a control of the water supply 
 such as cannot be had by dependence upon the wind and at the 
 same time they can be of such size and capacity as to be within the 
 reach of the individual farmer. 
 
 Pumping plants of this character have been installed at a first cost 
 of from $50 to $100 per _^ acre, and upward. The cost of operation 
 and maintenance per acre is usually larger than that of the windmill 
 and compares favorably with that of the steam engine but is higher 
 than from gravity sources, ranging from $5 to $10 per acre. These 
 forms of engines are undergoing rapid improvement and develop- 
 ment, so that the engineer in considering the practicability of install- 
 ing machinery of this kind should be advised of the most recent 
 experience in order not to repeat the errors of his predecessors. 
 
 The gasoline engine using distillate is reported to be doing about 
 80 per cent, of that part of the pumping in southern California which 
 is not being done by electric power — thus indicating a considerable 
 advantage over the steam engine. These distillate engines use the 
 cruder distillate from petroleum and are built up to as high as 300 
 
Plate IX 
 
 Fig. A.- 
 
 -Pumping water by wind mill into earth tank from which an irrigating 
 stream can be drawn. 
 
 Fig. B. — Gasoline pumping equipment, delivering water into small earth 
 
 reservoirs. 
 
 (Facing Page 124.) 
 
Plate IX 
 
 
 '"' d^. 
 
 Fig. C. — Generators driven by water power furnishing electrical energy for 
 pumps. Minidoka Project, Idaho. 
 
 Fig. D. — Electrically operated centrifugal pumps delivering water to laterals on 
 Gila River Indian Reservation, Ariz. 
 
IRRIGATION BY PUMPING 125 
 
 h.p., thus irrigating large tracts of lands. Although the large 
 distillate engine which requires the services of an engineer is not as 
 economical as a high-grade steam plant using the cruder unrefined 
 oils, yet as the irrigation of much of the country is subject to inter- 
 ruption, the lower first cost of the plant and the short time it is used 
 offsets the higher fuel cost. 
 
 Many of the owners of orchards in southern California are supply- 
 ing themselves and neighbors with water by engines which are not 
 visited sometimes more than twice in a day's run of ten hours. The 
 engines are reliable and fairly economical, if ordinary attention is 
 given them. A still higher economy may be obtained when there 
 are introduced various forms of producer gas from either oil or coal. 
 
 Water Power. — The ust of water power is, theoretically at least, 
 the most economical of methods for pumping water. Usually it i= 
 considered in connection with development of electricity and the 
 transmission of power to points where the pumps are to be operated, 
 forming thus a hydroelectric combination. There are cases, how- 
 ever, where it is advisable to install a water-power development at 
 the point where the water is to be pumped. For example, on a main 
 canal the topography of the ground may be such as to necessitate or 
 make desirable the putting in of a drop in the bed of the canal. 
 Power can be developed at this drop to lift a portion of the water 
 to the lands above the level of the main canal. Automatic pumps 
 for this purpose have been devised and successfully operated at 
 relatively small expense, such for example in connection with the 
 Huntley Montana Reclamation project, where, with the drop of 
 30 ft. in the main canal, a portion of the water is lifted to a height of 
 50 ft. above the canal to irrigate higher lands as shown in Fig. 35. 
 
 The device used at Huntley consists of a turbine wheel attached to 
 the lower end of the vertical shaft on the upper end of which is a 
 centrifugal pump, the water passing into the turbine wheel actuates 
 it, driving the centrifugal pump which in turn is fed by a portion of 
 the water which is flowing toward the turbine. This portion, about 
 one- third of the capacity of the penstock, is forced upward to a higher 
 level. 
 
 This machine is enclosed within a cylindrical case, so that all parts 
 of the machinery are protected and when once installed the pump 
 runs continuously with a minimum of attention throughout the 
 irrigation season. 
 
 Hydraulic rams can also be installed in localities of this kind, this 
 device depending upon the water hammer or ram of the water. 
 
126 PRINCIPLES OF IRRIGATION ENGINEERING 
 
IRRIGATION BY PUMPING 127 
 
 which when falling rapidly is suddenly checked, the momentum 
 causing a portion of the water to be forced to a higher elevation. 
 These rams have reached a capacity as high as 5 cu. ft. per second 
 of delivery, and are found to be very economical for installation. 
 They are very noisy and the shock of the arm rapidly wears the 
 moving parts unless these are carefully adjusted. They are easily 
 clogged or put out of order and on the whole have not given a high 
 degree of efficiency for continuous operation for any considerable 
 period of time. 
 
 Compressed Air. — Where compressed air can be readily obtained 
 from an established plant, it has been found feasible to lift water from 
 deep tubular wells by means of what is known as the air lift. For 
 example, in the vicinity of sugar-beet factories or large mills where 
 there is an excess of power or of compressed air, during certain parts 
 of the year arrangements have been made for utilizing the air for 
 lifting water for irrigation. The device consists essentially of an 
 arrangement of vertical pipes by which compressed air is carried by 
 means of a small pipe to near the bottom of the well casing, and there 
 released. The air ascending through the water confined in the larger 
 pipe forming the well tends to lift the water, causing it to overflow 
 the top of the pipe. The advantages claimed are a large capacity, 
 low maintenance cost, especially in sandy water which cuts the valves 
 of mechanical pumps, and low operating cost, particularly where an 
 air compressor is readily available. The disadvantages lie in the low 
 efficiency, the relatively great depth required, as the air pump cannot 
 be used in a shallow well or reservoir, and the impracticability of 
 using highly inclined or horizontal course for the water. 
 
 The efficiencies as measured by various experimenters generally run 
 from about 25 to 33 per cent., being higher in some laboratory experi- 
 ments, but lower in actual practice. A comparison between the 
 efficiency of wells pumped with air lift and deep steam pumps at 
 Waukesha, Wisconsin, showed an efficiency of 16 to 18 per cent, for 
 air lift based on the indicated horse-power in the steam cylinder, and 
 an efficiency of nearly 75 per cent, for deep well pumps. (See 
 Bulletin 450, University of Wisconsin, Oct., 1911.) 
 
 Hydroelectrical Power. — The use of power transmitted by 
 electricity in pumping water for irrigation or the hydroelectric plant 
 from an economic or engineering standpoint, is one of the ideal com- 
 binations of mechanical completeness and efficiency. Like most 
 ideals, it is yet to be worked out completely, although the results 
 already attained demonstrate the great possibiUties. It occasionally 
 
128 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 happens that in planning an irrigation system, there is necessarily- 
 involved a drop of water from the point of storage back into the river 
 or canal, or at some point along the main conduits. 
 
 Occasionally falls of water on the canal lines occur at points where 
 direct pumping is not possible but where water-wheels may be in- 
 stalled, power developed and transmitted for the operation of pumps 
 placed more conveniently to the irrigable lands. Under such con- 
 ditions, the engineer should plan for the conservation of this power 
 and prepare estimates as to the practicability of utilizing the power 
 in bringing the water to the lands which otherwise could not be 
 reached. 
 
 As an example of one of the recently developed hydroelectric 
 plants built primarily for pumping water for irrigation is the station 
 of the Minidoka project in southern Idaho, a plan and section of 
 which are given in Fig. 36. A view of the interior of the power 
 house is shown on Plate IX, Fig. C. This is located at the rock- 
 fill dam across Snake River near Minidoka. This dam has a height 
 of 86 ft. with length of rock-fill of 736 ft. and contains 242,500 
 cu. yd. of material. (See Plate XV, Fig. A.) It raises the water 
 surface about 40 ft. forming a body of water known as Lake Wal- 
 cott. A certain amount of water claimed by prior appropria- 
 tors must pass through this dam for use at points below. In so 
 doing power is developed for use in pumping water to the lands 
 lying above the reach of gravity water from Lake Walcott. 
 
 The excess power, especially that obtained during the non-irri- 
 gating months is used for furnishing heat, light, and current to the 
 towns on the project. Seven thousand kilowatts are generated in 
 five separate units, and transmitted about 13 miles at 33,000 volts 
 to three pumping stations. The first lifts about 650 cu. ft. per 
 second to a height of 31 ft. above the gravity canal; at this level 
 about 10,000 acres are irrigated. The balance of the water is 
 pumped to an elevation of 31 ft. where another canal irrigates 
 about 15,000 acres. The remainder of the water is pumped an 
 additional 31 ft. to the highest level, from which about 23,000 
 acres are irrigated. The building shown in Fig. 36 is located on 
 the down-stream side of the concrete controlling works across Snake 
 River. The building is of reinforced concrete and consists of a 
 turbine floor and generator floor and galleries as shown in Plate 
 IX, Fig. C. The building is 150 ft. long, 50 ft. wide, and 85 
 ft. high on the down-stream side. The turbines when fuUy loaded 
 are rated at 2,000 h.p., and used 425 second-feet of water under 
 
IRRIGATION BY PUMPING 129 
 
 the normal head. The main electric units are 1,200-k.w. 2,300- 
 volt, 3-phase, vertical alternators of the revolving field type, and 
 are operated at 200 revolutions per minute. 
 
 In some localities, where it is not practicable to develop electrical 
 power directly, it is possible to arrange for purchase of it from a 
 source external to the project, and to obtain this at rates notably low, 
 because of the fact that the power can be utilized in pumping at 
 times of day or during seasons when there is least demand for it for 
 use in other purposes, for example, in any large electrical power 
 development for ordinary commercial purposes, provision is made 
 for a certain maximum demand which usually occurs during the 
 winter and within certain portions of each day. At times during 
 each day, or after midnight and from then nearly to sundown there 
 is an excess of power which may be had at small cost or at rates 
 sufficiently low to justify pumping for irrigation. 
 
 There are several modifying conditions, however, which must be 
 very carefully considered, the first of these is that of securing long 
 time contracts or provisions such as will justify agriculture operations. 
 It would be unwise to build a pumping plant for an orchard which 
 will not come into bearing for several years, nor reach maturity for 
 ten or twelve years, unless there is assurance that the power supply 
 will be adequate and can be had at reasonable rates for a long period 
 of years. 
 
 Where water-power can thus be had in connection with irrigation 
 development, the engineer should give careful consideration to the 
 economies which may result by extending the irrigable area to lands 
 which, lying above the main canal, usually possess points of supe- 
 riority either in soil, exposure or drainage. It frequently happens 
 that excess- water accumulates on the low lands, reducing the value 
 of these. It is sometimes possible, under such conditions, to utilize 
 cheap power transmitted by electrical devices in draining these lands, 
 this waste water being used for the reclamation of additional areas. 
 Where drainage waters are used for irrigation, attention must be 
 given to their quality, as they frequently contain large quantities of 
 harmful alkali salts in solution. 
 
 In considering hydroelectric developments of this character, 
 the units commonly employed are the cubic foot per second for rate 
 of flow and the horse-power or kilowatt (i. h.p. = 0.746 kw. or i kw. = 
 1.340 h.p.). Assuming the weight of water as 62.5 lb. per cubic foot, 
 this amount falling i ft. per second develops 0.1136 h.p. = 0.0847 kw. 
 Putting it another way, i cu. ft. per second falling 8.8 ft. generates 
 
130 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 o 
 
 J3 
 
 J4 
 
 § 
 
 3 
 
 •a 
 
 B 
 
 O 
 
 o 
 
 1^ 
 
IRRIGATION BY PUMPING 131 
 
 one theoretical horse-power, or i kw. per hour equals i acre-foot 
 raised i ft. high. If for convenience in preliminary calculations a 
 motor eflSciency of 80 per cent, is assumed, i second-foot falling 
 II ft. will generate i h.p. or 0.746 kw. (or i kw. = 1.340 h.p.). 
 If the power is used for pumping water and the plant efficiency is 
 taken at 50 per cent, for motor, pump, etc., then i acre-foot raised 
 I ft. high will require at least 2 kw.-hours. By this simple rule the 
 total power required to irrigate an acre may be apprehended by 
 easy mental effort. 
 
 In estimating the energy created by falling water, it is convenient 
 to make certain assumptions, as to the efficiency of the various 
 forms of apparatus. The turbine water-wheel is assumed to have 
 an efficiency under good conditions of 80 per cent, or over, some 
 have reached in practice 87 per cent, or even 90 per cent, on tests. 
 The generator may reach an efficiency of 90 to 95 per cent. From 
 this it is customary to transform the power to a higher voltage for 
 purposes of transmission and the transformer may be considered as 
 having 96 to 98 per cent, net efficiency. There are certain losses in 
 transmission line which may vary from 5 to 10 per cent., and it is 
 fair to assume a transmission-line loss of this amount. Transforming 
 the power again and reducing its voltage is another loss of 2 or 3 
 per cent, or more, so that the horse-power ultimately transmitted 
 will be about as follows: 
 
 ASSUMED EFFICIENCIES 
 
 Turbines 80 per cent, net efficiency 80 . o 
 
 Generator 93 per cent, net efficiency 74.4 
 
 Transformer 97 per cent, net efficiency 72.2 
 
 Transmission line 92 per cent, net efficiency 66.4 
 
 Transformer 97 per cent, net efficiency 64.4 
 
 Starting thus, with a theoretical 1,000 h.p. we arrive at the point 
 of use with about 644 h.p. applied to the motors. 
 
 The cost of power installation varies widely with the amount of 
 power developed, the character of machinery, and the surrounding 
 conditions. For preliminary assumptions it may be considered as 
 ranging from $45 to $80 per horse-power, depending upon the 
 amount of hydraulic work necessary in the way of dams, power 
 qanals, etc. The cost of a pumping plant where large pumps are 
 used may vary from $45 to $65 per horse-power, making the cost of 
 a plant, ranging in capacity from 1,000 to 5,000 h.p., from $100 to 
 
132 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 $175 per horse-power when completely installed, with transmission 
 lines and other accessories. 
 
 The cost of operation also varies greatly with the character of the 
 plant and the continuity of operation and amount of power used. 
 It is for this reason impiossible to give figures on the cost of operation 
 which will be of value in any particular case. In pumping for 
 irrigation the plant must lie idle a considerable part of the year, 
 unless it can be used for other purposes, for example, as an auxiliary 
 power for domestic or municipal supply. Under these conditions 
 it may be possible to dispose of power at very low rates during the 
 winter season sufficient to justify the operation of the plant in 
 order to maintain the operating force and prevent increase of operat- 
 ing cost due to new organization each year. 
 
 In estimating the cost per unit of horse-power or kQowatt-hour, 
 it is necessary to make certain assumptions concerning the load 
 factor, that is to say, the ratio between the actual amount of power 
 which can be developed continuously and the amount which is 
 habitually being used. In other words, if under normal conditions 
 machinery is capable of developing loo h.p. but the average demand 
 throughout the day is for only 75 h.p. the load factor may be con- 
 sidered as 75. During the day at short intervals there may be an 
 overload and the electrical machinery is usuaOy built to carry for 
 brief intervals an overload of 50 per cent, or more. Again the load 
 may drop down to a very small fraction of the total capacity of the 
 plant, so that the average throughout the day under general condi- 
 tions rarely approaches 100 per cent. 
 
 In estimating the economy of installation of a power plant, it is 
 essential to consider the probable cost of this in comparison with the 
 possibility of purchasing power, especially where it may be obtained 
 at irregular intervals, when not needed for other purposes, and at 
 correspondingly low prices. 
 
 Assuming that electric power can be purchased for pumping 
 at I cent per kilowatt-hour at the switchboard, and that the pumps 
 will be operated for six months in the year of 180 days continuously, 
 with a load factor of 75, the cost per 100 kw. for the season will be 
 $3,240. 
 
 The equivalent of this is 134 h.p. and this amount will raise 23-)- 
 
 second-feet of water to a height of 50 ft. serving for the irrigation, 
 
 assuming an average duty of water of about 2,300 acres, at a cost 
 
 of $3,240, or less than $1.50 per acre for power. 
 
 Cost of Pumping. — This is expressed either in terms of quantity 
 
IRRIGATION BY PUMPING 133 
 
 of water delivered at a certain point, such for example as $i per acre- 
 foot or 30 cents per million gallons, or more generally in the terms 
 of acreage served, as $2.50 per acre per season — the latter involving 
 an assumption as to the duty of water. In discussing the matter 
 from an agricultural standpoint, it is advantageous to use the cost 
 per acre for direct comparison with cost of irrigation by gravity 
 systems, and with the value of crop obtained. 
 
 As a rule, the cost of pumping water is higher than that of obtain- 
 ing it from gravity sources. The first, or construction cost, may 
 possibly be less than that of a gravity system, but the annual 
 expense for operation and maintenance, including depreciation, 
 is considerably higher. The cost is roughly proportioned to the 
 height to which the water is raised, so that the controlling factor is 
 largely the difference in elevation between the source of water in 
 the well, reservoir, or steam, and the point of delivery from which 
 it reaches the irrigable land. 
 
 Where the values of crops are very great as is the case in some 
 of the highly developed fruit sections and with sugar-cane in the 
 Hawaiian Islands, water for irrigation may be pumped to a height 
 of 500 ft. or more. With ordinary crops of the temperate zone the 
 present economical lift is considered as being not far from 60 or 70 
 ft. Theoretically, it should be profitable to pump to greater heights 
 than these, but practically, this has not yet been successfully 
 done. 
 
 In some sections the annual charges for pumping water is not 
 less than $25 per acre, as for example, in the foot-hill region near 
 Pomona and Ontario and in Orange County, California. In other 
 sections where more favorable conditions obtain, the charges 
 probably do not exceed $5 per acre per annum. Under exceptional 
 conditions they may be even less than this. 
 
 In Western Kansas the cost is stated to be not far from 7 cents 
 per acre-foot of water raised one foot in height, or $3.50 per acre- 
 foot raised to a height of 50 ft. These figures roughly indicate the 
 present condition of development of the small pumping plants. 
 They include operation and maintenance, depreciation and interest 
 on investment, costs of 5 cents per acre-foot raised one foot are not 
 unusual and with better economy the cost is stated to be as low as 3 
 cents or slightly less. These lower estimates are generally based not 
 on long-continued actual practice but on short-time or laboratory 
 tests. The general appearance of the pumping plant and reserve ir 
 is shown in Plate IX, Fig. B. 
 
134 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 It is difficult to obtain actual costs of pumping because of the 
 fact that many of the private plants have been operated in the 
 interests of the promoters or persons selling land and at a nominal 
 charge for the purpose of facilitating land sales. It is generally 
 agreed that at a later date when the land is sold the works will be 
 turned over to the land owners to be operated at their expense. 
 The losses which may be encountered in cost of operation during 
 the time when the plant is new and the lands are being placed on 
 the market are more than made up by the additional prices received 
 from the sale of lands. This fact is cited so that engineers may not 
 be misled by the relatively low annual charges occasionally quoted 
 for pumped water, these not necessarily representing the actual 
 cost, which in some cases may be twice as great. 
 
 Feasibility of Pumping. — The practicability of pumping water 
 for irrigation is governed primarily by natural conditions, such as 
 place of occurrence of water, height of lift, distance to the irrigable 
 land, and mechanical difficulties growing out of the^e, all being 
 summed up in the statement of probable cost. There may be an 
 ample supply of water, and relatively cheap power, but the lands 
 to be covered may be widely scattered in small tracts requiring 
 long pressure pipe or distributing system over ground too rough or 
 undulating to render the work successful, or the distance to markets 
 may be too great. It is necessary, therefore, in considering this 
 matter of obtaining water to take into account, as in the case of 
 gravity systems, the economic a? well as the engineering features, 
 such as the quality of the soil, the ease of irrigation, the climatic 
 conditions and markets governing the value of crops, and to study 
 these in connection with the more purely mechanical side. 
 
 As stated in the paragraphs regarding cost, it has not been found 
 feasible as a rule to pump water for ordinary crops in the temperate 
 zone to a height much greater than 70 ft., but there are conditions 
 where small tracts of land of exceptional quality and accessible to 
 markets will justify the building of a pumping plant for raising 
 water beyond this height. 
 
 The feasibility of extending the agricultural area by pumping is 
 governed by the comparison of total costs with returns. Of the 
 total costs, the item of power is frequently the large and controlling 
 one. It is apparent that while at present this cost must be kept at 
 a relatively low amount, as time goes on, as the soil is subdued 
 and rendered more productive, as the orchards reach maturity, and 
 as population increases and markets are established, it will be 
 
IRRIGATION BY PUMPING 135 
 
 possible to incur a larger and larger cost per acre and to utilize 
 sources of power which at the present time are considered as being 
 too expensive. 
 
 The growth of the country is accompanied by an improvement 
 in mechanical appliances and in the feasibility of purchasing waste 
 or excess power from various industrial processes. As before 
 stated, the excess power from lighting or transmission plants may 
 be purchased and used when not in demand for the primary purpose 
 for which the machinery was installed. These considerations 
 should be given due weight in all plans for developing irrigation by 
 pumping, and before stating the limit to any proposed system, these 
 ultimate sources of power shovdd be carefully studied. 
 
 The maximum height of lift which may be considered in planning 
 a pumping plant for irrigation has previously been given as ranging 
 from a present maximum of over 500 ft. for the most valuable 
 tropical plants, citrus fruits and intensive truck farming, down to 
 60 or 70 ft. for the ordinary crops of the temperate zone. The 
 controlling factor of height of lift is not set by mechanical con- 
 siderations, but in each case these enter into the designing of the 
 plant after determination has been made of the limit of cost which 
 may be incurred. 
 
 In southern California, in the vicinity of Los Angeles, water is 
 being pumped as high as 75 ft. for the purpose of raising alfalfa, and 
 as this is one of the crops which requires a large amount of water, 
 it may be assumed that if this can be successfully grown by pump- 
 ing water to this height, orchards and more valuable crops may be 
 cultivated with water lifted stiU higher. Each year the area of 
 alfalfa thus irrigated is being extended, indicating that the operations 
 are financially successful. 
 
CHAPTER VIII 
 DRAINAGE 
 
 Classification. — The subject of drainage may, in a general way, 
 be subdivided into two classes; namely, surface drainage and under- 
 ground drainage. These two classes are not entirely independent, 
 since it would be impossible to carry on any form of surface drainage 
 without producing a certain amount of underground drainage, and 
 equally impossible to carry on underground drainage without also 
 at certain times disposing of surface waters. 
 
 Surface drainage ordinarily applies to the removal from the sur- 
 face of the ground waters which have fallen upon it in the form of 
 rain or snow. Surface drains are usually comparatively shallow 
 open drains of sufficient capacity to take care of storm floods and 
 carry them away quickly and before they have time to soak to any 
 considerable depth into the soil. 
 
 Underground drainage applies to the removal of ground waters, 
 or those which are below the surface of the soil. These ground 
 waters may be the result of rains or irrigation in the immediate 
 vicinity, or they may be carried for some distance underground 
 and finally come near the surface on the lower areas in the path of 
 their flow. Underground drains may be either open or closed; 
 they differ, however, from surface drains in that the supply reaches 
 them not over the surface but through the lower soU or sub-soU. 
 
 Drainage problems in connection with irrigation usually require 
 the use of underground drains since it is the excess of irrigation 
 waters that have been put into the soils that have to be removed. 
 As this work is intended to deal only with problems of irrigation, 
 underground drainage will be the principal subject treated in this 
 chapter. 
 
 Needs of Drainage.^ — One of the first requisites for the growth 
 of crops is moisture. The soil must be kept sufficiently wet to 
 supply to the roots of a plant the water which it requires for its 
 existence and growth. 
 
 Soils are made up of minute particles very irregular in shape and 
 size. These particles when loosely thrown together, as is the case 
 in properly cultivated soils, leave spaces of irregular shape and 
 
 136 
 
DRAINAGE 137 
 
 dimensions between them. The size of the spaces depend upon 
 the size and shape of the particles forming the soil and the closeness 
 of the particles to each other. It thus follows that a closely packed 
 soil of the same material will absorb and hold less water than one 
 which is loosely broken up, for the reason that the volume of the 
 spaces between the particles is less in the former than in the latter 
 case. 
 
 Each individual particle comprising a soil, due to the law of 
 attration of matter, is capable of holding on its surface a minutely 
 thin film of water. The mutual attraction between the particle and 
 this thin film is so great that aU the water cannot be drained out of a 
 soil by gravity; in fact, to remove all of the moisture which clings to 
 the minute particles of a soil except by carefully heating and dry- 
 ing is a very difficult process. 
 
 When a soil contains no perceptible water adhering to its indi- 
 vidual particles, it is said to be dry; when it contains only so much 
 water as is held by the attraction of the particles and no more 
 will drain away, it is said to be moist; when the spaces between the 
 particles are completely filled with water, it is said to be saturated. 
 If an excavation be made in soil which is moist only, no water will 
 flow from the soil into the excavation. If the excavation be made 
 in soil that is saturated, water will collect and in a short time stand 
 at the same elevation as the top of the saturated soil. The surface 
 of free water or the upper limit of saturation in a soil is commonly 
 called the water plane. 
 
 Vegetation requires moisture, but with the exception of aquatic 
 plants, will not grow in soils that are saturated with water. In 
 order to grow crops in an arid or semi-arid region — where the 
 natural .rainfall is not sufficient to supply the necessary moistures 
 to the soils — this lack of water must be supplied by irrigation. 
 Important as the supplying of water to land may be, it is equally 
 important that any excess water which would cause the soil to be- 
 come saturated be removed. Theoretically it may seem possible to 
 apply to soils only the exact amount of water required for the growing 
 of crops. Practically it is found that in nearly every case there is a 
 certain amount of excess water which must be disposed of. When 
 the soil is open or porous to a sufficient depth to permit the excess 
 waters being carried away, natural drainage may be said to exist. 
 Where nature has not provided natural underground drainage, it 
 must be supplied artificially. 
 
 The fundamental problem in drainage is to control the elevation 
 
138 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of the water plane and keep it below the zone of soil required for the 
 roots of growing plants. If this is not done the roots cannot pene- 
 trate to the required depth to obtain the necessary nourishment 
 from the soil. 
 
 In soils which. contain harmful alkali salts, it is necessary also 
 that the water plane be kept down in order to prevent on accumula- 
 tion of these salts on the surface. 
 
 Alkali and its Effect. — ^As heretofore stated the soils of the arid 
 and semi-arid regions are largely the results of disintegration of 
 rock. Many of them have not been completely washed by copious 
 rains during their formation and contain large quantities of soluble 
 mineral salts. Some of these salts, especially in limited quantities, 
 are beneficial and necessary for the growth of vegetation, while 
 others are harmful, and in sufficient quantities will prohibit its 
 growth. Sodium carbonate, commonly known as black alkali, is 
 the most detrimental of all the alkali salts to plant growth. The 
 exact action of alkali on a plant is not clearly understood, its effects, 
 however, is to destroy the root tissues near the surface of the soil 
 and leave the plant to die for lack of food and moisture. On account 
 of the action of alkali being near the surface it is essential that any 
 accumulation of salts in the top stratum of soil be avoided. (See 
 Plate X, Fig. A.) 
 
 In their natural state the alkali salts are distributed more or less 
 uniformly through the soils, frequently extending to considerable 
 depths. When water is applied to the land, the soluble salts are 
 dissolved. As the process of evaporation goes on from the surface 
 of the soil and waters charged with alkali are brought up by capillary 
 action there is a gradual accumulation of salts on or near the surface 
 until finally the soil is unfit for the growing of crops. If the soil 
 becomes saturated or, in other words, if the water plane is brought 
 near to the surface, the capillary action in drawing water to the 
 surface and consequently the rate of evaporation and deposit of 
 alkali is increased. 
 
 Benefit of Drainage. — Reference has already been made to the 
 necessity of artificial drainage on certain classes of soils to prevent 
 their becoming unfit for use through the rise of the water plane and 
 the accumulation on the surface of harmful alkali salts. On certain 
 other classes of soils crops can be grown without drainage, but the 
 soils are greatly improved and the value of the crop yield increased 
 by its use. In such cases drainage may be classed as a benefit 
 rather than a necessity. In this respect it may be compared to any 
 
Plate X 
 
 Fig. a. — Alkali flat, formerly a valuable farm, now ruined by careless irrigation 
 and lack of drainage. 
 
 ^*^^mt^ ***«s«g^!^ 
 
 
 ^ 
 
 W'° 
 
 Fig. B. — Distributory lined with concrete to reduce loss of water and prevent 
 development of alkali. 
 
 (Facing Page 138) 
 
Plate X 
 
 
 
 
 
 
 
 ..«l MM* -v. •!■»•• -W -ap- 
 
 -i-j;.a 
 
 
 "■'■"- ■'"■'■ 
 
 ., 
 
 ^^*^^-— — -— ■ 
 
 
 
 ^ 
 
 
 ,. ••'' ■■-■ ■ 
 
 ^T^^m^' ' % ■ 
 
 
 Jp 
 
 .„JJ^ 
 
 
 
 \'m " 
 
 
 ff , 
 
 
 
 - . T%«iJ| 
 
 'r* 1 
 
 ^' ^ 
 
 V . , <i» ^ 
 
 
 ^^ 
 
 
 1; \ ■: 
 
 
 fe^/ 
 
 . ^jI^mBI 
 
 
 
 Fig. C. — Weir and self-registering gage. Williston Project, No. Dak. 
 
 Fig. D. — Automatic gage for recording height of water in river or main canal. 
 Laramie River, Colo. 
 
DRAINAGE 139 
 
 other method of improving the soil or increasing the amount of 
 crop that can be grown. For example, on many soils crops will 
 grow without the use of fertilizer, but it has been found that by 
 its use the value of the crop may be increased by many times the 
 cost of the fertilizer applied to the land. 
 
 Soils that are especially benefited by drainage are those which on 
 account of their compactness do not allow a free movement of water 
 through them. Soils must contain, in addition to moisture, a 
 certain amount of air, in order that they be in proper condition to 
 grow crops. It is necessary also that they be sufficiently loose and 
 porous to allow the plant roots to penetrate them freely. It is 
 possible for a soil to become so firmly compacted that there are 
 practically no spaces between its particles and consequently it is 
 impossible for either air or water to enter freely. Soil in this condi- 
 tion is commonly designated as water-logged, although the amount 
 of water it contains is small on account of the lack of spaces between 
 the particles to take up and hold moisture. A water-logged soil is 
 cold due to the lack of the circulation of air through it. For this 
 reason crops cannot be started as early in the spring on a water- 
 logged sou as on a loose and porous one. 
 
 By providing for the removal of water from the lower strata of 
 a water-logged soil by means of drainage and at the same time break- 
 ing up the surface by deep plowing or sub-soiling, the pores of the 
 soil may be opened and a downward movement of water started. 
 Air will be drawn into the soil, following the movement of water 
 through it and in this manner the soil will be warmed and brought 
 to the proper condition for growing crops. 
 
 Another important advantage of getting a downward motion of 
 water started and air drawn into the soil by drainage is the removal 
 of impure or objectionable vegetable matter. The roots of vege- 
 tation, it appears from recent agricultural investigations, leave in 
 the soil a certain amount of organic matter, a portion of which is 
 detrimental to some kinds of plant growth. The aeration of the 
 sou carries into it the necessary elements for reducing the organic 
 matter left in the soil by vegetation to a state that is less harmful 
 to the growth of crops. 
 
 Summarizing, drainage may be said to be a protection against 
 injury to land by raising the water plane too near the surface, and 
 the bringing to the top soil, through capillary action and evapora- 
 tion, harmful alkali salts. It is also an insurance of larger and better 
 crop yields by keeping the pores of the soU open, thus permitting 
 
140 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 it to be warmed and purified through aeration, and kept in proper 
 condition. It will also be shown later that drainage is beneficial 
 in reducing the amount of water which must be applied to the scU 
 in the process of irrigation. 
 
 Grovind Water. — The term ground water as here used applies 
 ordinarily to water below the surface of the soil. The upper limit 
 of ground water is the top of the zone of saturation in the soil or 
 what has already been defined as the water plane. In some special 
 instances the water plane may rise until it is above the ground sur- 
 face, as for example in low depressions. The elevation of the ground 
 water in such cases will be regulated and controlled by sub-surface 
 waters in the higher adjacent areas. Water which has been brought 
 to or above the surface by the rise of the water plane and the eleva- 
 tion of which is controlled by an underground movement of water 
 may properly be classed as ground waters. 
 
 The depths of ground water varies greatly in different formations, 
 and in a comparatively small area, say of i or 2 square miles, may 
 range anywhere from i to 100 ft. or more. It depends largely 
 upon the depth to impervious material,' such for example, as a 
 strata of clay or rock. It also depends upon the rate at which 
 water wDl move through the pervious top strata, and the quantity 
 of water which reaches the area, either in the form of rain or as 
 applied for irrigation. 
 
 If a sub-soil is porous, the excess water which finds its way into 
 it will gradually pass downward until it reaches an impervious 
 stratum which prevents further downward motion. When the 
 surface of the impervious stratum is level or inclined downward, 
 the water will move laterally over it until it finally finds its way to 
 some natural outlet and is carried away. In this manner the water 
 plane, if the supply which reaches the surface is not too great, may 
 be kept down through natural process. If the surface of the imper- 
 vious stratum is irregular consisting, as is frequently the case, of 
 depressions and ridges, the lateral movement is prevented and the 
 water plane will rise until an outlet is found over the crest or through 
 gaps in the impervious barriers. It thus follows that even with a 
 
 ' Note. — Materials which are absolutely impervious to water are seldom found 
 in nature. For want of a better term impervious material is used in this chapter 
 to designate material which is tight enough to prevent the passage of but a very 
 limited quantity of water through it, such for example as firm clay or rock in 
 place. 
 
 There is no sharp line of demarcation between pervious and impervious mate- 
 rials as found in nature; both are therefore to be considered as relative terms only. 
 
DRAINAGE 141 
 
 seemingly porous sub-soil of considerable depth the water plane 
 may be held up near the surface by the existence of impervious under- 
 ground ridges or dikes. 
 
 When the amount of water which reaches a sub-soil is greater 
 than can be carried away laterally over the impervious stratum, 
 even though its surface be level, the sub-soil will become saturated 
 and the water plane rise until it reaches the surface or until equi- 
 librium of inflow and outflow is established. In the arid or semi- 
 arid regions where irrigation has not been practised, ground waters 
 are usually found at a considerable distance below the surface; 
 this is on account of the limited rainfall and correspondingly small 
 amount of water which reaches the sub-soils. 
 
 The rate of lateral movement of ground waters depends upon the 
 porosity of the material and also the grade or slope of the water 
 plane. A compact formation resists the flow of water first on ac- 
 count of the total cross-sectional areas of the openings through it 
 being small, and second, on account of the minute size of each of 
 these openings, since greater pressure is required to force water 
 through them. On account of the complex nature of this subject, 
 it is impossible to apply any theory to determine the porosity of 
 a soil, in so far as it will affect the passage of water. Even in the 
 most porous soils such as sand or gravel, the rate of water move- 
 ment is very slow amounting to only a few feet per day, while in the 
 most compact clays it is scarcely perceptible. 
 
 The elevation of the water plane relative to the surface of the soil 
 is frequently affected by the varying thickness of a more or less 
 porous stratum through which ground waters are moving. This 
 condition is illustrated by considering a shallow sub-stratum of 
 sand or gravel underlain by a stratum of imprevious material and also 
 capped by a soil of clay or other semi-imprevious soil. The ground 
 waters will move through the stratum of sand or gravel as this offers 
 the least resistance to flow. If the thickness of this porous stratum 
 is uniform or nearly so the movement of the waters will be uniform 
 and but little if any upward pressure will be exerted against the less 
 pervious top stratum. 
 
 At those places where the thickness of the sand or gravel stratum 
 is diminished, due to thinning of the beds or the presence of imper- 
 vious dikes or barriers projecting upward into it, the flow will be 
 checked and the ground water will be put under slight pressure 
 which will tend to force it to the surface. Examples are frequent in 
 the irrigated portions of the arid west where waters have traveled 
 
142 PRINCIPLES OF IRRIGA TION ENGINEERING 
 
 underground for long distances and are finally forced to the surface 
 on account of the porous sub-soil being obstructed or pinched out. 
 Conditions of this kind are more likely to occur on or near the foot of 
 slopes but are also frequently found on nearly level or uniformly 
 sloping land. 
 
 Information relative to ground waters on a particular area can be 
 obtained by means of borings put down to sufficient depths to show 
 the elevation of the water plane and the character of the soil and 
 sub-soil materials over that area. It is ordinarily possible from a 
 study of these data to find the direction of movement of groimd 
 water and to determine the cause of the rise of the water plane too 
 near the surface. In many cases the source of the ground water can 
 also be ascertained; this, however, is not always possible on account 
 of the long distance it sometimes travels before coming to the 
 surface. It is impossible on account of the many unknown factors 
 involved to form accurate conclusions relative to the move- 
 ment of ground waters from surface indications or from theoretical 
 considerations. 
 
 Effects of Drainage on Soils. — Reference has already been made to 
 the benefits to be derived from drainage. The effects of drainage 
 on soils which serve as a benefit may be enumerated as follows: 
 
 1. Removal of excess water. 
 
 2. Breaking up less pervious materials and increasing porosity. 
 
 3. Washing out impurities. 
 
 4. Increasing the capacity for retaining water. 
 
 The most important of these is the removal of excess waters from 
 the soil. Most useful plants cannot survive in a soil saturated with 
 water. The first consideration in drainage is to draw down the 
 water plane below the depth to which the roots must penetrate. By 
 keeping the water plane well down the roots are encouraged to go 
 deeper for water. The result is a more hardy plant than could be 
 grown if it were required to obtain its entire nourishment from a thin 
 layer of soil near the surface. 
 
 The breaking up and rendering the soil more porous is accomplished 
 by the downward motion of the water through it. This breaking up 
 of the soil is also accomplished to a certain degree by the roots of 
 plants penetrating it. Nitrogen is also carried into the soil by the 
 roots of certain plants and the soil is thereby enriched. The down- 
 ward motion of the water and plant growth work together in a well- 
 drained soil to disintegrate it, rendering a thicker stratum available 
 for plant food. 
 
DRAINAGE 143 
 
 Impurities existing in the soil since its formation, as well as those 
 which accumulate, are washed out by the downward motion of water. 
 The soil is thereby kept in healthful condition so that plants can 
 thrive in it. 
 
 One of the greatest benefits of the breaking up of a soil and render- 
 ing it more porous is its increased capacity for retaining moisture. 
 In a loose soil the particles are sufficiently separated from each other 
 so that when water is applied each particle holds a minute film of 
 moisture clinging to its surface. The water thus held cannot be 
 drained away and evaporation takes place slowly. The result is 
 that moisture will be retained available for the use of plants much 
 longer in a porous than in a non-porous soU. On account of the 
 greater amount of moisture held by the particles there is less waste 
 of water also. Moisture is consequently held in suspension which 
 otherwise in a compact soil would be wasted over the surface or 
 would have passed off laterally through the surface layers. It 
 follows from this that the total amount of water which must be 
 applied for the growing of a crop may if properly applied be less 
 in a porous than a non-porous soil. Well drained land, strange 
 as it may appear, requires less water to irrigate it than that which 
 is undrained. 
 
 Open and Closed Drains.— The relative merits of open and 
 closed drains are questions largely of economy in construction and 
 operation. The action of a drain of given depth and capacity in 
 drawing waters laterally to it and lowering the water plane is, so 
 far as known, the same whether it be open or closed. This is assum- 
 ing that each is kept in proper condition to take up the excess 
 waters from the soil and carry them away. It is claimed by some 
 that open drains under certain conditions become silted along the 
 bottom and for some distance up the side slopes so that water can- 
 not enter them freely. Examples have been found where the ground 
 water immediately adjacent an open drain stood above the water 
 surface in the drain; this, however, was due to an upward pressure 
 against a relatively impervious top soU. The drains where this 
 condition existed were not cut deep enough to intercept the pervious 
 stratum below. 
 
 In considering the relative cost of construction of open and 
 closed drains there must be taken into account in the former the 
 value of the lands which they occupy in addition to the cost of 
 building the drains. Open drains are a detriment to agricultural 
 operations on account of cutting up the lands, and the opportunity 
 
144 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 which they offer for the growth of noxious weeds and grasses. The 
 maintenance of open drains intending to regulate and control the 
 elevation of ground waters is diflScult on account of the tendency 
 to become partly filled with weeds or other obstructions. When 
 this occurs the effective depth of the drain is decreased, and its 
 efficiency for drawing down the water plane is lessened. Open 
 drains have an advantage over closed drains in that their capacity 
 is not limited to a pipe or conduit of fixed dimensions, but increases 
 as the water plane in the soil adjacent to the canal rises. 
 
 On steep slopes it may be necessary to construct drops in 
 open drains in order to prevent erosion; in closed drains this is 
 ordinarily unnecessary, the increased grade being an advantage 
 in increasing the velocity of flow and reducing the size of drain 
 required. 
 
 Closed drains permit all the land over which they are constructed 
 being used, and obviate the objectional cutting of the land by open 
 channels. When properly constructed they require little or no 
 maintenance and are always in a condition to perform the function 
 for which they are intended. In determining the question whether 
 an open or closed drain is to be used in any particular case, the 
 advantages of each from the relative cost of construction and main- 
 tenance and the probable efficiency for the purpose intended should 
 be considered. 
 
 In general, it may be said that the closed forms are cheaper and 
 better adapted for small drains intended to remove excess waters 
 from the soil and hold down the water plane. Open trenches are 
 ordinarily cheaper for the larger trunk drains where a considerable 
 capacity is required. 
 
 The materials from which closed drains should be constructed 
 will depend to a certain extent upon what is available in the particu- 
 lar locality where used. Clay and cement tiling, sewer pipe and 
 wooden boxes have all been successfully used. The choice of one 
 of these Is largely a question of first cost and permanency of con- 
 struction. Hard-burned clay tiles of good quality, so far as known, 
 are not affected by any of the various constituents found In the 
 soils and when placed deep enough to protect them from frost and 
 surface cultivation may be considered as being as permanent as 
 ordinary masonry construction. Cement tiling may also be con- 
 sidered permanent In soils which do not contain alkali. In some 
 of the soils of the west, however, cement has been found to be dis- 
 integrated by the action of alkali upon It. Cement tiling for this 
 
DRAINAGE 145 
 
 reason cannot be recommended for use in lands containing alkali 
 to any appreciable degree. 
 
 Vitrified sewer pipe with bell joints does not possess any advan- 
 tages over hard-burned clay tiling with straight joints. It costs 
 more than the ordinary tiling, and is more diflBcult to put in place 
 on account of cutting out for the flanges in the bottom of the trench. 
 The flange joints are also more likely to become silted than ordinary 
 straight joints. One example has been reported of a drainage line 
 made from ordinary vitriiied pipe where the joints became sealed 
 by silting so that no water could enter it. Wood on account of its 
 tendency to decay cannot be considered as suitable material for 
 closed drains where permanency is required. The decay of wood 
 in a drainage line is hastened by the fact that portions of the drain 
 may be dry during a part of each year. 
 
 On account of the nature of the work being such that close in- 
 spection cannot be made of it from time to time and the difiiculty 
 in finding and repairing breaks in a closed drain, permanent con- 
 struction should be used wherever possible. 
 
 Relief and Intercepting Drains. — Drains are sometimes classed 
 as relief and intercepting depending upon the manner in which 
 water reaches them. A relief drain is one which taps a wet area 
 directly and permits the ground water to flow out from different 
 directions into the drain. An intercepting drain is one intended 
 to cut off an underground flow and carry away the water before it 
 reaches an area where the formation is such that it will rise to the 
 surface. Relief drains are adapted to lowering and keeping the 
 ground water at a safe distance below the surface. They are for 
 the most part constructed in the lower portion of an area to be 
 drained in order to draw down the ground water to the lowest 
 elevation possible. Intercepting drains, on the other hand, are 
 constructed above the area which they are intended to benefit. 
 
 Relief drains are of value in loosening and increasing the porosity 
 of the soil by producing a downward motion of water through it. 
 Intercepting drains are, in general, of no value for this purpose since 
 they do not as a rule perform the function of drawing down ground 
 waters over any considerable area. 
 
 It is impossible to compare the relative merits of these two classes 
 of drains, on account of the different functions which they perform. 
 Where the drainage problem is to draw off excess waters from a 
 large area and improve the character of the soil by lowering the 
 water plane and inducing a downward motion of water through it, 
 
146 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 intercepting drains are not to be considered. Where it is necessary 
 to remove ground waters which are known to be traveling at a 
 comparatively shallow depth it can frequently be done by means of 
 an intercepting drain constructed crosswise to the direction of the 
 flow. In order that an intercepting drain may work effectively it is 
 essential that its bottom be below the pervious stratum through 
 which the ground water moves. Where this is not the case, the 
 flow will continue through the pervious material both from the lower 
 side of the drain and also under it. On account of this limitation, 
 conditions are seldom found where it is feasible to entirely cut off 
 a flow of ground water. Intercepting drains may frequently be 
 used to advantage in cutting off the greater portion of the ground 
 waters flowing down a slope, the amount of drainage required on the 
 more level lands below being thus greatly reduced. 
 
 Drainage Investigations. — Before attempting to make plans for 
 the drainage of a particular area as full information as possible 
 relative to the character of the soil and position of the water plane 
 should be obtained. In gathering facts relative to soil conditions 
 it is essential to ascertain whether the soil is uniform in character to 
 the depth that drainage works should be constructed, or whether 
 it is distinctly stratified with layers of clay, sand or gravel; and if 
 so, the porosity of the different strata. The necessity for this in- 
 formation lies in the fact that the movement of ground waters 
 takes place more freely in some of these layers than in others. In 
 planning drainage works it is necessary to take account of the 
 different carrying capacities for water of the various strata of which 
 the soil is composed. Where a somewhat heavy and impervious 
 soil, such, for example, as clay or adobe is underlain by a strata of 
 gravel through which water moves freely, it is of the utmost impor- 
 tance that the location of the gravel be known and that it be taken 
 into consideration in planning works to remove the excess water. 
 
 In addition to information relative to the character of soil, it is 
 necessary to carefully determine the elevation of water plane over 
 the area to be drained. After determining these facts it is possible 
 to show graphically, either by contours of water surface or by cross- 
 sections, the elevation and slope of the ground waters, and from this 
 arrive at the direction of movement and the most feasible location 
 for drains. It is important also that, if possible, the source of ground 
 waters be determined. This can ordinarily be done by a study of 
 the elevation of water surface and the character of the soil through 
 which the ground waters move. * 
 
DRAINAGE 147 
 
 The information required for designing a drainage system usually 
 can be best obtained by means of borings at short distances apart 
 over the proposed area. The frequency of these borings and the 
 depth to which they should be carried will vary in different localities, 
 due to local conditions. They should be carried down to a sufficient 
 depth to show the elevation of the water plane and the character of 
 soils for some distance below the depth it is necessary to drain. 
 They should be made sufficiently near each other to enable the eleva- 
 tion of the ground waters and the character of the underground 
 formation to be known at any particular point with a reasonable 
 degree of accuracy. 
 
 The portraying of the water plane for drainage purposes is not 
 unlike the mapping by means of contours, of the surface of the 
 ground for other purposes; such, for example, as the planning of 
 irrigation canals and laterals. It must be understood, however, 
 that the work of determining the contours of a water plane is far 
 less accurate than the ascertaining of surface contours. The same 
 is also true of the determination of the elevation and thickness of a 
 sub-soU of sand or gravel. It is essential, however, in planning 
 drainage works that as accurate data as possible be had. The 
 source of underground waters which rise sufficiently near the surface 
 to interfere with agricultural operations is, in many cases, difficult 
 to determine. By drawing a series of water contours or cross sec- 
 tional proffies indicating thereon the elevation of water plane over 
 a given area, it is ordinarily possible, however, to trace out the 
 high-water areas and from these a general knowledge is had of the 
 local conditions and the direction of percolation of the ground 
 water. 
 
 Capacity of Drains. — In arriving at the capacity of a given drain, 
 consideration must be given, first, to the area to be drained, and, 
 second, to the amount of excess waters to be removed. In 
 estimating the area to be drained by any given drains or system 
 of drains, it is necessary to take into account not only the area upon 
 which the drains are constructed but the total area of land whose 
 underground waters are tributary to these drains. As before stated, 
 ground waters frequently travel for long distances at a considerable 
 depth and finally come to the surface on a comparatively small area 
 below. In determining the capacity of drainage works for this 
 small area, particular attention must be given to the quantity of 
 water which reaches it from an external source. At best, informa- 
 tion of this kind which can be collected is only a rough estimate, 
 
148 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 since the amount of water which flows away from an irrigated area 
 in any particular direction cannot be accurately measured. 
 
 The amount of excess waters resulting from a given depth on the 
 soil, either from natural rainfall, or irrigation, or both, is also a 
 question fraught with many uncertainties. Various assumptions 
 have been made as to the amount of water returned from irrigation. 
 It is doubtful, however, if sufficient accurately planned observations 
 have been made on this subject to warrant definite conclusions being 
 based upon them. In general, it is believed that by careful super- 
 vision of the operation of applying water to lands, the underground 
 waste should not exceed 25 per cent, of the total amount applied to 
 the surface. If this assumption be correct, and the amount of water 
 applied to a particular tract during a year is 2 acre-feet, it is sufficient 
 to plan a drainage system to remove 1/2 acre-foot per acre, or, in 
 other words, a depth of 6 in. over the entire surface. 
 
 Irrigation ordinarily takes place during the summer months only, 
 say from about the ist of May until the ist of October, a period of 
 five months. It is not necessary to make drainage works of sufficient 
 capacity to remove all of the excess waters during the irrigation 
 period, since the soil has a large storage capacity and drains will be 
 in operation for all, or a greater part, of the year. It is believed 
 where the period of irrigation extends over less than six months of 
 the year that twice the length of irrigation season may be allowed 
 for the period of operation of drains. That is to say, where irriga- 
 tion is carried on for a period of five months, a period of ten months 
 may be given for the drains to remove the excess waters. If it is 
 required to remove the equivalent of a surface depth of 6 in. within 
 this period, capacity must be provided in drainage ditches of i cu. ft. 
 per second for each 1,200 acres. The above estimates of the 
 amount of water to be removed as previously stated, are not based 
 upon actual measurements but are believed to be conservative. It 
 is to be understood that for similar soil conditions the greater the 
 quantity of water used in irrigation the greater the capacity of 
 drains required. 
 
 Depth of Drains. — The depth to which drains should be con- 
 structed depends, first, upon the character of the soil as regards 
 water movement through it; second, upon the capillary action of the 
 soil in drawing water to the surface; and, third, upon the depth 
 below the surface that the water plane must be maintained. Where 
 the soil is underlain by a stratum of pervious sand or gravel con- 
 taining water under shght pressure, it is ordinarily necessary to 
 
DRAINAGE 149 
 
 construct drains deep enough to tap this sand or gravel stratum and 
 reUeve the pressure in order to prevent water being forced to the 
 surface. Drainage under these conditions is not a question of 
 putting down drains to a depth of water plane required, but rather 
 a question of removing waters from below so as to prevent their 
 being forced upward through the soil stratum to the surface. Con- 
 ditions have been found where water has been forced up to a con- 
 siderable height above the grade of surface drains excavated in a 
 somewhat pervious soil. 
 
 In such cases the lateral movement of water to the drains is 
 not sufficient to carry water to the drains as rapidly as it is forced 
 upward into the soil. Where a pervious sub-soil condition does not 
 exist and ground waters do not reach the area from an outside 
 source, attention must be given to drawing off the excess waters 
 applied to the surface only. When this is the case, it is necessary 
 to decide to what maximum elevation the water plane must be 
 kept. This must, in every case, be below the zone of plant growth. 
 It is necessary also that it be low enough so that the capillary action 
 will not carry water to the surface in sufficient quantities to cause 
 it to become seeped or bogged. 
 
 The distance that water will rise by capillary action varies in 
 different kinds of soil. It ordinarily ranges from about i 1/2 to 
 
 3 1/2 ft. In general, it is believed on irrigated land, the minimum 
 depth to water plane should not be less than 4 ft., while, for certain 
 kinds of crops, a greater depth may be advisable. The holding of 
 the water plane down in this manner allows the plant roots to 
 penetrate deeper into the soil and produces a more vigorous plant 
 than can be obtained when growth is confined to a shallow depth. 
 The depth of drains required to maintain a depth of water plane of 
 
 4 ft. will depend upon the amount of water applied to the soil, the 
 freedom of movement of water through the ground, and the distance 
 between drains. 
 
 The above are all questions which must be determined for each 
 particular case and it is consequently impossible to lay down any 
 hard and fast rules relative to the depth of drains. In general, it is 
 believed, however, that on irrigated lands, drains to be effective 
 should have a minimum depth of not less than about 5 ft., while in 
 a majority of cases a greater depth is required. 
 
 Distance between Drains. — The proper distance between drains 
 in order that they may be effective and at the same time permit of 
 the most economic construction is, in most cases, difficult to de- 
 
150 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 termine. It depends primarily upon the rate of water movement 
 through the soil and also to some extent upon the depth of the 
 drains and source of ground waters. Heavy surface soils underlain 
 at a comparatively shallow depth by an impervious material re- 
 quire the most frequent drains. This is especially true if the waters 
 to be removed come from excess irrigation or rainfall directly on 
 the area. With conditions of this kind drains are sometimes re- 
 quired at intervals of from 50 to 100 ft. in order to keep the water 
 plane down to the required depth. 
 
 Where there is a sub-stratum of pervious material at a reason- 
 able distance below the surface so the drains can be cut into it they 
 may be effective at long distances. Under conditions of this kind 
 the effect of drains may extend from half a mUe to a mUe on either 
 side of them. The actual distance that the water plane will be 
 lowered will, of course, depend upon the depth of the drain. 
 
 A rough idea of the distance a drain will draw water can be had 
 from an examination of the soil. Accurate information, however, 
 can only be obtained by observation on the water movement and 
 slope of the water plane. This can frequently be determined by a 
 row of test wells at right angles to a natural drainage channel. 
 Where topographic and other conditions will permit, it is some- 
 times advisable to construct short drains for the purpose of study- 
 ing their effect before making final plans for complete drainage. 
 Observations on the effect of main or trunk drains may also be used 
 to determine the frequency of smaller drains that wiU be required. 
 
 Grades and Velocities of Flow in Drains. — The most important 
 considerations in determining the grades of drains is to provide on 
 the one hand, sufficient velocity to prevent the drains becoming 
 clogged and, on the other, to avoid excessive velocities such as tend 
 to erode the channels. The first consideration applies to both 
 open and closed drains, while the latter applies more especially to 
 open channels in earth since closed drains are ordinarily of materials 
 that win withstand relatively high grades and velocities. When 
 the grades of earthen ditches are too high there results a cutting 
 of the bottom or sides of the channel which undermines the banks 
 causing them to fall. There thus results an irregular and unsightly 
 ditch where the growth of noxious weeds and plants is encouraged. 
 There may also be a considerable waste of land along the sides of 
 the ditch. If there are any sections of the ditch where the grades 
 are relatively flat the materials eroded above will be deposited in 
 these sections and make the problem of maintenance more difficult. 
 
DRAINAGE 151 
 
 The limiting grades which may be allowed in drainage ditches 
 like irrigation canals will vary with the amount of water carried 
 and the character of the materials through which the drains are 
 constructed. Special attention must be given to each particular 
 case in order to determine the proper grade to be used. 
 
 Where it is necessary to reduce the grade in an open ditch to 
 prevent scouring, some form of drop shoidd be used. This may be 
 either- a vertical fall with a water cushion below or a short length 
 of channel buUt on a steep grade and protected by means of suitable 
 material to prevent erosion. 
 
 The question of grades and velocities in open drainage ditches 
 does not differ greatly from these same questions when applied to 
 irrigation canals. It must be borne in mind, however, that the 
 capacity of a drainage ditch is ordinarily much less than that of an 
 irrigation canal and that in the former depth rather than carrying 
 capacity is the principal factor to be considered. On account of 
 the small capacity of drainage ditches the amount of grade which 
 they will withstand is ordinarily much greater than in irrigation 
 canals. Drainage ditches are ordinarily excavated into firm 
 materials which erode less freely than the artificial banks of irri- 
 gation canals. For this reason also the dangers of cutting in the 
 former are less than in the latter. 
 
CHAPTER IX 
 OPERATION AND MAINTENANCE 
 
 Distribution of Water. — The primary purpose of constructing, 
 maintaining and operating a canal system is to provide water for 
 irrigation. The ultimate test of the success of the system from 
 an engineering, and ordinarily from a financial standpoint, depends 
 upon whether the water can be supplied to the lands under it at 
 the proper time when needed. This depends, first, upon the 
 character of the design and construction, and second, upon the 
 efi&ciency of operation and maintenance. Whatever the importance 
 of properly designing and constructing irrigation works, the im- 
 portance of properly maintaining and operating them is equally as 
 great. 
 
 Operation and maintenance requires the determination of the 
 best methods and policies to be pursued, and involves questions 
 of an administrative and engineering nature. Both of these are 
 complicated on account of the right of the farmer to receive water 
 from the system at the exact time when needed. The delivery of 
 water therefore must be given first consideration, and the methods 
 to be followed in making deliveries, and in maintaining canals 
 must be such as to permit operation being carried on continuously. 
 To the farmer who is dependent upon an irrigation supply of v/ater 
 for his success and livelihood nothing but most extraordinary con- 
 ditions are sufiicient to justify the cutting off of this supply even 
 for a single day at the time when it is required for the growing of 
 crops. 
 
 There are a number of ways by which water for agricultural 
 purposes is distributed to lands. These are to a limited extent the 
 results of careful experiment and scientific investigations; and to a 
 greater extent the outgrowth of the crude methods used by the first 
 irrigators. The subject of best handling water for irrigation 
 purposes is in a formative state, and much work remains to be done 
 by engineers and irrigation managers to devise means best suited to 
 each particular case. In order to improve present methods it is 
 necessary to devise others better suited to conditions, and also to 
 overcome the prejudice which commonly exists against changes in 
 agricultural operations. 
 
 152 
 
OPERATION AND MAINTENANCE 153 
 
 Generally speaking there are two quite distinct systems for the 
 distribution of water to lands, viz., continuous flow and periodic 
 rotation. In order to consider the relative merits of these two 
 systems and results which may be expected from each, it is essential 
 that there be taken into account the conditions of the soil necessary 
 for the growing of crops, and also the effect of water continuously and 
 periodically applied to it in producing these conditions. 
 
 Contiiiuous Flow. — The distribution of water by the continuous 
 flow systems assumes that a stream of water of sufficient quantity 
 to supply the needs of a given area is kept constantly flowing upon 
 it. Take for example a tract of say 50 acres, and let us assume that 
 it is desired to deliver to it 5 acre-foot per acre during a period of 
 thirty days. The volume of flow required to deliver this quantity 
 
 is — ^ ' — = 0.42 second- feet, an amount usually too small for 
 
 economical handling. For a larger or smaller area a proportionately 
 larger or smaller flow is required. 
 
 The distribution of water by continuous flow imitates natural 
 brooks or creeks. It was the system naturally adopted in the early 
 stages of irrigation development in the United States. The smaller 
 streams were diverted from their channels and carried out in long 
 lines of canals, which were divided and sub-divided, each carrying a 
 small amount of water to its respective owner. These canals were 
 diverted in meandering courses across the fields and when water was 
 not required on the lands it was allowed to waste back into the 
 stream. The amount of water which was delivered to a given area 
 was not restricted to that which could be beneficially used and 
 seldom was there an attempt made to conserve the water supply. 
 When water was plentiful (as was the case during the flood season) 
 the farmer used all he wanted without special attention being given 
 to the amount which should be applied to the soil, and when water 
 was scarce, it was regarded as a condition for which no one was to 
 blame. 
 
 As irrigation developed, and the demands for water increased, it 
 became the custom to limit the amount which each man might 
 receive, this quantity being defined by a stream of given size. From 
 the standpoint of the farmer who desires water continuously on his 
 land so that irrigation can be carried on at any time, regardless of 
 whether or not the soil is in proper condition for irrigation, such a 
 system has its advantages. Also where water is considered as a 
 commodity to be owned by an individual without reference to 
 
154 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 whether or not he can use all, or a part of it to advantage, a continu- 
 ous flow system is well adapted to measuring to each individual that 
 which he owns. The disadvantages of using this system for deliver- 
 ing water for irrigation, however, are many. 
 
 In order that the soil may be in proper condition for growing 
 plants, it is necessary that it be kept supplied with moisture to the 
 depth penetrated by the plant roots. It must not, however, be 
 given suflScient water to become saturated. The only practical 
 plan of obtaining this condition is to apply to the surface, at more or 
 less regular intervals, a sufficient supply of water to moisten the soil 
 to the required depth. The moisture thus applied is held in suspen- 
 sion by the soil particles until taken up in part by the plant roots 
 and in part by evaporation from the surface. When the supply of 
 moisture becomes exhausted so that the plants can no longer find 
 .sufficient to sustain them, another irrigation is required. 
 
 By the continuous flow system portions of the land over which 
 the water flows become saturated, or too wet for plant growth to 
 thrive upon it. This is due to the fact that the soil is not given an 
 opportunity to free itself from the excess water which is applied to 
 it. In addition to the injury of lands to which water is directly 
 applied, injury to those adjacent thereto is frequently caused. The 
 result, therefore, is ruinous to the lands of the irrigator using this 
 system, and possibly also to those of his neighbor. 
 
 The quantity of water required for the irrigation of a small tract 
 of land, as for example the ordinary farm, when delivered continu- 
 ously produces a stream too small to permit its being properly 
 distributed. This is especially true on farms the soil of which 
 absorbs water rapidly. 
 
 In general it may be said that the continuous flow system of 
 delivery is wasteful of water, detrimental to the soil and not well 
 adapted to carrying on irrigation operations. 
 
 Periodic Rotation. — This method of delivering water, as the 
 name implies, is to supply to the land at somewhat regular inter- 
 vals the amount of water it requires to keep it in proper condition 
 for plant growth. It differs from the continuous flow system 
 previously described in that the smaller canals, especially those to 
 individual water users, carry water during only a portion of the time. 
 When water is required on a given area a sufficient quantity is 
 diverted to cover it in the shortest possible time, and the supply 
 is then passed on to the next irrigator. 
 
 The advantages of this method may be enumerated as follows: 
 
OPERATION AND MAINTENANCE 155 
 
 1. It permits of more even distribution of water, since the lands 
 adjacent to the smaller canals do not become saturated as is the case 
 where water is flowing continuously in them. 
 
 2. The soU is kept in better condition by being allowed to become 
 warmed and aerated during the period when water is not applied 
 to it. 
 
 3. It permits of more economic irrigation, since the farmer re- 
 ceives his supply in sufficient quantity to permit its being carried 
 quickly over the lands. 
 
 4. The system is economical in the use of water, due to the fact 
 that unnecessary waste and losses from the smaller canals is avoided, 
 and water is delivered only when and where it is needed. 
 
 The delivery of water by periodic rotation imitates on a small 
 scale the efforts now being made to conserve the water supply of 
 a given stream or watershed, so as to make it serve the largest possible 
 area. To accomplish this the water is held in storage and diverted 
 to the streams or canals only when actually required for irrigation. 
 
 The partial drying of the soil after one irrigation and before the 
 next is applied permits greater freedom of cultivation, which serves 
 to reduce the quantity of water required. Thorough cultivation, 
 to a certain degree, can be made to supplement a deficiency in 
 water supply, by reducing evaporation from the surface. 
 
 The period of rotation in any particular case will depend upon 
 climatic conditions, character of soU, and kind of crops raised. 
 The essential requirement is that water be applied to the soil at 
 periodic intervals when required. 
 
 Length of Irrigation Season. — The actual time during the year 
 that irrigation is required, or the irrigation season, as it is commonly 
 called, varies greatly in different localities. It depends primarily 
 on the climate in regard to temperature and seasonal rainfall. 
 
 In the regions where long cold winters prevail the irrigation 
 season is necessarily limited to the late spring and summer months 
 and no water should be placed upon the lands until they have been 
 warmed sufficiently by the approach of summer to stimulate plant 
 growth. In a climate having a more or less definite season of rain- 
 fall, during the spring or early summer irrigation is frequently not 
 needed until the rainy season is passed. 
 
 Where the climate is sufficiently mild to allow crops to grow 
 during the winter season, as is the case in some of the arid regions 
 of the southwest, irrigation may be required throughout the entire 
 year. Ordinarily, in this section the natural rainfall is too 
 
156 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 small or too erratic in character to take the place of a single 
 irrigation. 
 
 During the irrigation or growing season water sufficient for the 
 plants should be applied to the soils; as soon as the growing season 
 is over it should be shut out of the canal system so that the soil 
 may become dry and aerated. With the approach of spring it is 
 then warmed and early planting may result. If irrigation is 
 practised during the non-growing season the presence of the excess 
 moisture in the soil renders it less porous and less responsive to the 
 sun's action. 
 
 In the more northern and colder portions of the United States 
 the irrigation season extends from about the ist of May to the ist 
 of October. Going southward the season gradually lengthens until, 
 as above stated, it is continuous throughout the year. 
 
 The proper time to begin irrigation in the spring and to discon- 
 tinue delivering water in the fall are questions of importance in 
 operation and maintenance work. It may happen that the bene- 
 fits of late fall irrigation to one season's crop ma,y be more than 
 offset by the damage it does in retarding the first crop of the follow- 
 ing year. No definite rule can be formulated as to when irriga- 
 tion shall be begun or ended. A careful study of soil conditions 
 and the results that may be accomplished is the only guide. 
 
 Frequency of Irrigation. — There is a wide variation in the time 
 which may elapse between irrigations. It depends upon the climate, 
 soil and character of crops raised. Coarse, porous soils, such for 
 example as sands or gravels, hold but little moisture in suspension. 
 In a climate where the rate of evaporation is high, the moisture near 
 the surface is rapidly exhausted. Shallow plants on soils of this 
 kind require irrigation at intervals of a few days. By some farmers 
 it is held that root crops planted in porous soil require water at 
 intervals of from one to two days. Experience has shown that 
 that is excessive and that better results can be obtained with less 
 frequent irrigation. 
 
 For alfalfa, the stable forage crop of the west, it is sufficient in the 
 more northern localities to apply water once for each cutting. 
 Further south in the warmer regions each crop is ordinarily irrigated 
 twice or more, water being applied in some cases every ten days 
 during the warmer months. 
 
 It is evident that for complete success the frequency of irrigation 
 must be adapted to the character of crops, time of planting, etc. 
 The schedule for supplying water to the fields in the district must be 
 
OPERATION AND MAINTENANCE 
 
 157 
 
 arranged with a full knowledge of the crops growing in that district. 
 In other words, there must be complete cooperation and good busi- 
 ness management between irrigation managers and farmers, acting 
 individually or in groups. If one crop is of such a character or is so 
 planted as to require irrigation during a certain week, the schedule 
 for water deliveries must be arranged accordingly or the crop will 
 suffer. If the crops are of such nature as to require daily application 
 of water, some special provisions must be made for supplying them. 
 In other words, it should be remembered that the primary purpose 
 of irrigation is to supply crops with water, and no rules relative to 
 times of delivery should be so iron-clad as to interfere with this 
 purpose. 
 
 An example of one of the schedules actually used by the United 
 States Reclamation for the operation of the Williston pumping 
 plant. North Dakota, is as follows: 
 
 "The operation of the Williston canal system for the season of igii, 
 will begin June 4. In order to secure economical and uniform operation, 
 deliveries of water from the different canals will be restricted in so far 
 as practicable to the dates listed below, water to be delivered in rota- 
 tion, beginning at the lower end of the system, running continuously 
 until irrigation is completed, and in such quantities as can be most 
 advantageously handled. 
 
 "Water will be delivered from: 
 
 Canals B & S, and Canal A, South of 
 Station No. 2. 
 June 4 to June 13 
 June 24 to July 3 
 July 14 to July 23 
 August 3 to August 12 
 
 Canals D & E, and Canal A, North of 
 Station No. 2. 
 June 14 to June 23 
 July 4 to July 13 
 July 24 to August 2 
 August 13 to August 22 
 
 "Application cards, stating whether water is desired during a ten-day 
 run, must be mailed and received at the project office two days prior to 
 the beginning of each ten-day run, and the water-user will be notified 
 in advance when delivery will commence. If it is not convenient to 
 take water at the time designated, it will be necessary to wait approxi- 
 mately twenty days until the next ten-day run." 
 
 Duty of Water. — The term ' ' duty of water " is a form of expression 
 for the quantity of water required for irrigation. It is sometimes 
 expressed as the area which a continuous flow of a given amount 
 will irrigate. For example, it may be said that the duty of water is 
 I second-foot for each 100 acres, meaning that i second-foot con- 
 tinuous flow will irrigate 100 acres. Another way of expressing 
 duty of water is by means of the depth applied to the land, that is, 
 the number of acre-feet per acre for a given period of time, for 
 
158 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 example, a month or a year. The larger the area irrigated by a 
 given quantity the higher the duty of water is said to be. 
 
 The determination of the proper amount of water to be used in 
 irrigation is perhaps the most diflSicult question to be solved by the 
 farmer and irrigation manager. It is affected by the kind of crop, 
 character of soil, the rate of evaporation in the particular locality 
 and also the skUl of the irrigator. When water is applied to the 
 soil a part of it is taken up by the growing plants, a part is consumed 
 by evaporation from the surface, and a varying amount is lost by 
 being carried downward through the sub-soU and eventually returned 
 as drainage water to the streams below. 
 
 It is estimated that to produce i lb. of dry vegetable matter 
 requires from 300 to 500 lb. of water. Using this as a basis, it would 
 require from about 2 1/2 to 4 1/2 in. in depth over the land to produce 
 I ton of dry matter per acre. It is of course impracticable to apply 
 the theoretically exact amount of water to the land on account of 
 evaporation and other losses which cannot be measured. 
 
 It is ordinarily impossible to irrigate lands without some water 
 being lost by its penetrating below the zone of the plant roots. 
 Various estimates of the amount of such losses have been made, 
 but on account of the varying conditions met with it is impossible 
 to apply them with safety to any particular case. It is beheved 
 that the loss by percolation below the plant root zone should not 
 exceed 25 per cent, of the total quantity placed on the land, and 
 that under careful irrigation on average soils it may be made much 
 less than this. 
 
 The determination of the proper amount of water to use, as a 
 practical question, can best be solved by observations on the condition 
 of the soil under varying water deliveries. In doing this care should 
 be taken to see that more water is not applied at any one irrigation 
 than the soil can absorb and hold in suspension. 
 
 Investigations made during the past few years seem to show that 
 in most irrigated sections where the quantity of water is not limited, 
 more is used than is necessary. The result of this excess use is a 
 decrease rather than an increase in crop production. It also has 
 the effect of impoverishing the land by leaching out valuable con- 
 stituents or rendering them waterlogged or alkaline. 
 
 On the projects of the United States Reclamation Service the 
 amount of water required for a season's irrigation varies according 
 to the best data available from 1.5 to 3.5 acre-feet per acre, the 
 average being about 2 acre-feet per acre. 
 
■OPERATION AND MAINTENANCE 159 
 
 In addition to the losses due to the application of too much water 
 to the soil there are also frequently large losses in transportation. 
 Water is carried for the most part not in tight pipes or impervious 
 conduits, but in open ditches built through more or less porous soils, 
 and distributed by furrows passing often through sand or gravel 
 areas in which a small stream may completely disappear. 
 
 The quantity which must be delivered to canals is, thus, greatly 
 in excess of the quantity theoretically needed on the land. To carry 
 this amount to a point where needed, it is necessary to send it in 
 considerable volume, or "head" so that it can flow quickly across 
 the more porous places. The larger the head of water in a canal the 
 greater the velocity and the smaller the percentage of loss due to 
 seepage. 
 
 As seepage losses only occur from the wetted perimeter of a ditch 
 or furrow, it is obvious that the quantity of water can be greatly in- 
 creased in the canal without notably adding to this wetted perimeter 
 and consequent loss; also, if the amount needed to irrigate a field can 
 be applied in half the usual time, it is apparent that the losses from 
 this source will be reduced. Quickness in applying water results in 
 economy, and the quantity needed is dependent largely on the skill 
 and rapidity of application of the water. This in turn is governed 
 to a certain extent by the size and location of the canal and structures, 
 slope of ground and character of soU. 
 
 Measurements of losses by seepage and evaporation indicate that 
 these losses in some cases are very great and that one of the most 
 important steps for securing economy in the use of water is in 
 reducing these losses. As long as open canals are used there must 
 be a steady loss through evaporation. The expense of reducing 
 these losses by covering the canals or putting the water in closed 
 pipes will probably be far in excess of the value of the water under 
 present conditions, but the seepage losses from the sides and 
 bottoms of the canals should be reduced wherever practicable, as 
 these are frequently of injury, not merely in the loss of the water 
 itself but in the seeping and rendering swampy or alkaline of lands 
 even at considerable distance from the canals. 
 
 Measurements of losses have been made on various canals giving 
 results of which the following are examples: 
 
 From the feed canal on the Umatilla project. Ore., the loss by 
 seepage and evaporation in the season of 1909 was 13.2 per cent, of 
 the amount taken into the canal, this begin equivalent to 396 acre- 
 feet per mile of canal or 98 acre-feet per acre of wetted area of canal. 
 
160 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 On the distributing system of the same project the losses by seepage 
 and evaporation amounted to 41.4 per cent, of the amount taken 
 from the reservoir. 
 
 On the Minidoka project, Idaho, the loss between the amount 
 taken into the main canal and turned to the sub-laterals was on the 
 north side gravity system 29 per cent, and on the south side 47 per 
 cent. 
 
 On the North Platte project, Wyoming and Nebraska, the losses 
 on the main canal were from 4 to 14 per cent, and on the laterals 
 from 5 to 39 per cent., dependent on the character of soil traversed. 
 The average elsewhere was about 18 per cent. 
 
 On the Truckee-Carson project, Nevada, the average losses on 
 a portion of the distributing system were 20.7 per cent., and on the 
 Okanogan project in Washington from the main canal and distribut- 
 ing system were 45 per cent. 
 
 An average series of measurements made on the Yakima pro- 
 ject, Washington, in 19 10, showed that of the total amount of 
 water taken into the main canal and branches 22.4 per cent, was 
 lost, of that taken into the lateral system 3: per cent, was lost, and 
 of that taken into the sub-lateral system 15 per cent, was lost. 
 
 Measxirement of Water Used. — Measurements of water used in 
 agriculture are as essential to the proper conduct of a system of 
 irrigation of any considerable size as are measurements of the 
 supplies sold by a produce dealer. Without accurate measurements 
 and records confusion and loss quickly result. In the case of a very 
 small system, there is obviously not the same necessity for making 
 measurements any more than there is of the individual householder 
 carefully weighing out the supplies for current use. But where 
 hundreds of individuals . are concerned, and where apparently in- 
 significant errors may accumulate in a large general loss, there 
 common sense and business rules demand accuracy and system in 
 management and in accounting. 
 
 In the accompan)dng Plate X, Figs. C and D, are shown measur- 
 ing devices as used on some of the irrigation canals. At Fig. C is a 
 weir and self-registering gage such as has been installed on the 
 Williston project. North Dakota, where water is pumped from the 
 Missouri River. Fig. D is a view of an automatic gage such as is 
 used at one of the stations on the Laramie River in Colorado. 
 
 The amount of water held, or turned out of the reservoirs, or 
 received at the head of a system, must be recorded from day to 
 day. Following down the main trunk line, there should also be 
 
OPERATION AND MAINTENANCE 161 
 
 measurements at several points in order to check losses through 
 seepage, and to verify the measurement at the head. As the water 
 is turned out in each of the principal branches, it should again be 
 measured so that for each district, or division of the canal system, 
 the amount of water received each day should be known and losses 
 again checked. Finally, the amount measured to each farm or group 
 of farms, together with the time of delivery, must be recorded in 
 order to have accurate data to settle the innumerable disputes 
 which may arise. 
 
 The measurements of larger quantities of water discharged from 
 a reservoir or received into the head of a canal are usually made 
 by some form of weir or submerged orifice. Where the latter is 
 used it is usually calibrated by means of a current meter. The 
 width and depth of the stream is obtained by direct measurement 
 and the velocity of all parts by any one of a considerable number 
 of devices on the market, most of these consisting of a rotating 
 wheel, the speed of which varies with the velocity of flow. All 
 such instruments must be rated, that is, the ratio between the speed 
 of the water and the number of turns of the wheel per second being 
 determined by direct measurement for each instrument. 
 
 Wherever there is ample fall, it is preferable to make measurements 
 by means of a weir, following the conventional forms, and using 
 tables computed from formulae based on experimental data giving 
 the ratio of water flowing to a depth on the weir. 
 
 The measurement of these large volumes of water is relatively 
 simple, and follows well-established practices. The greatest diffi- 
 culties, however, are encountered in measuring economically the 
 smaller quantity of water directly to the field of the farmer. There 
 are a great many devices for this purpose, but those which yield 
 fairly accurate results are quite expensive. The problem of in- 
 troducing and using these on an old canal system is similar to that 
 of attaching meters to the service pipes in a city. Theoretically 
 this should always be done, but practically the cost of the instru- 
 ments and care required has been a great obstacle. In the same 
 way, the cost of procuring, installing, and maintaining a suitable 
 measuring device or module at each farm has been so great as to 
 be almost prohibitory for the ordinary irrigation system. 
 
 The devices used for measuring water to the farmers have usually 
 been somewhat crude, being manufactured locally, and consisting 
 of measuring boxes made of plank or boards, in which by adjusting 
 small wooden, or iron gates, the water is allowed to escape through 
 
162 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 a rectangular orifice. Where there is sufficient head, it is sometimes 
 allowed to flow over a small weir, and for each of these weirs a table 
 is made to show the quantity of water discharged. Where it is not 
 possible to provide a fall or drop in the water from the canal or 
 lateral to the field, the water is sometimes conducted in a wooden 
 flume on a nearly level grade, in which measurements are 
 made of the width and depth, and the velocity ascertained by small 
 floats, or by current meters devised for the purpose. In this latter 
 case a table is prepared showing the quantity of water flowing for 
 different depths in the flume. 
 
 Human Element. — In the practical working out of an irrigation 
 system, and in the distribution of water to the land the most 
 serious consideration is not the engineering or mechanical difficulties, 
 but those which arise from having to deal with considerable numbers 
 of men of more or less limited education, coming from all parts of 
 the world, frequently with strong native prejudices, or with experi- 
 ence under conditions entirely different from those had under 
 successful irrigation. Many of these men must unlearn much 
 which they regard as of first importance. Others have none of 
 the qualities which lead to success in farming. Some are of a roving 
 disposition who are attracted by the novelty of a change in vocation 
 or by the glowing advertisements of land speculators. 
 
 Under these conditions factions arise, and under even the most 
 patient and tactful management there are always a number of 
 farmers or settlers who attribute their lack of success not to them- 
 selves but to the operation and management of the irrigation works. 
 
 Since the salary paid to a superintendent or manager of a system 
 is not always sufficient to attract and hold a diplomat of high order 
 especially one who also possesses the skill of an engineer and the 
 practical knowledge of an experienced farmer, it from necessity 
 follows that there is more or less friction in the management. The 
 man who can handle a large irrigation enterprise without complaints 
 from the farmers can readily obtain a salary elsewhere far too great 
 to justify his remaining on an irrigation work ! 
 
 This condition must be borne in mind at all times in the opera- 
 tion and management of any work of this kind, which has to do 
 with the untrained men working under pioneer conditions. With- 
 out any organization or means of control — each man is free to act 
 as he pleases — ^planting his own crops in his own way, and at his 
 own time. Under these circumstances, no system, however well 
 planned, can meet the individual demands of the farmers. There 
 
OPERATION AND MAINTENANCE 163 
 
 must always be criticism and complaints which require the exercise 
 of unusual patience and forbearance on the part of the management. 
 It must not be supposed that because complaints are continually 
 made, that the system is badly planned or poorly operated. The 
 engineer himself must clearly distinguish between those criticisms 
 which are important, or vital, and those which arise simply from 
 having to do with a mass of humanity not yet educated by experi- 
 ence in that particular climate, soil, and surrounding. 
 
 Maintenance. — The maintenance of an irrigation system is theo- 
 retically distinct from the operation, but practically is very inti- 
 mately connected with it, as the maintenance must be carried on 
 in the same place and often at the same time with the operation. 
 
 Theoretically a canal should be operated during the crop season 
 by a force proportioned to the number of distributions to be made 
 and the number of miles of canals and laterals to be operated, and 
 this force should report all defects, accidents, or worn-out apparatus, 
 and as a result of this, the maintenance to be taken up as a sepa- 
 rate item. As a matter of fact, however, it is economical and often- 
 times necessary for the operating force to make many of these re- 
 pairs or adjustments when they are discovered, although it is de- 
 sirable to have what is sometimes called in railroad work "an extra 
 gang" ready to go to any point to repair or renew structures needing 
 attention. ^ 
 
 The successful operation is dependent not only upon proper 
 construction originally, but also upon immediate and effective 
 maintenance of all of the structures. There is more or less deprecia- 
 tion at all times, and the gradual weakening of one part or another 
 is sometimes of such a nature that the work can be done at almost 
 any time during several months, or even years. 
 
 Successful and economical maintenance depends upon having 
 accurate knowledge of the character and extent of the gradual as 
 well as of the accidental depreciation, and of organizing the work 
 so that immediate attention is given to breaks or critical places. 
 At other times the men should be employed in improving the prop- 
 erty where wear or decay is taking place, so that the maintenance 
 cost may be kept at a fairly uniform rate. 
 
 It occasionally happens that a careful and competent superintend- 
 ent who has thoroughly understood the work, and who for the good 
 of the system has been forced from year to year to make certain 
 expenditures in maintenance, is replaced by a man who desires to 
 make a record for economy. The new management can cut down 
 
164 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 the maintenance cost notably for the time, but the inevitable result 
 happens that the entire property depreciates in value, and in the 
 course of a year or several years, breaks or accidents occur one after 
 the other, the total cost of these being far greater than the apparent 
 saving previously made. In comparing the cost of maintenance in 
 different years or different systems, this fact must be always borne 
 in mind, and careful analysis made to ascertain whether the mainte- 
 nance has been careful and complete, or whether it has neglected 
 some essential point, and exposed the system to larger loss. 
 
 Priming. — The expense of maintenance is materially affected 
 by the care and skill shown in priming the canal, especially in skill- 
 fully bringing the water against all new works. Large amounts 
 of money have been lost by lack of care in this regard, by attempting 
 to use canals before they have been properly primed. 
 
 In the case of new banks, especially those which have not been 
 thoroughly wet and compacted in construction, the water should 
 be brought against them very slowly, being raised from day to day, 
 and carefully watched. In the case of long sections of new or re- 
 cently repaired canal, it may be necessary to provide temporary dams 
 of timber and boards, or of sacks of earth, by means of which the 
 water level can be raised a few inches at a time, watching carefully 
 all possible locations where there may be signs of weakness, and 
 reducing the water level at once, if leaks are discovered; at the same 
 time puddling the points where there appear to be holes or pervious 
 places. The points of greatest danger are at the juncture between 
 the earth and the concrete, masonry, or wooden structures. Here 
 extreme care must be used in bringing water against the points 
 of junction, raising it with great slowness and with devices such 
 that the level can be immediately reduced if there is any tendency 
 to break through. 
 
 Care of Banks. — The maintenance of earthworks is a matter 
 requiring continual vigilance. Nature is perpetually endeavoring 
 to level down all surface elevations of this character, and most of the 
 ordinary operations of men aid this leveling. Cattle tramping over 
 the earth tend to loosen it, permitting the winds to blow it away, or 
 cause it to roll down the slopes. 
 
 The canal banks frequently afford convenient roads and in many 
 instances it is a matter of necessity for the men in charge of the work 
 to travel on the canal banks. This has a certain advantage in 
 compacting the soil, but it tends to make paths, or ruts, which catch 
 the rain-water. If the banks are to be used for roadways, they 
 
OPERATION AND MAINTENANCE 165 
 
 should be made higher and wider than is required for canal purposes 
 only. 
 
 The banks should be kept as symmetrical as possible, slightly 
 crowned on top and sown with grass-seed, or the growth of grass 
 and clover encouraged. Until plants of this character have taken 
 possession, the larger and more injurious weeds rapidly spread, and 
 it is necessary occasionally to cut these, especially those which break 
 off when dry and blow into the canal. 
 
 In the warmer climates Bermuda grass has been tried and while 
 this is very successful in protecting the banks it becomes a serious 
 menace to the fields of the farmer under conditions where the frost 
 is not sufficiently heavy to kill it during the winter. 
 
 Cleaning Canals. — It is necessary to clean most canals annually 
 or oftener not only to remove the accumulated silt but under some 
 conditions to get rid of the aquatic plants or moss, the latter term 
 including a great variety of growth. 
 
 This so-called "moss" growing in the bottom of the canal forces 
 the water to be carried above the normal level, presenting fresh 
 surfaces of the canal bank to the water and increasing the losses by 
 percolation, also the danger of breaks by the water finding its way 
 into holes or points of weakness left by burrowing animals. 
 
 The destruction of this moss is a serious problem in some locali- 
 ties; the attempt has been made to prevent its growth by lin- 
 ing the canal with cement, but this is not wholly effective as shown 
 by the fact that on the Twin Falls Canal in Idaho the only place 
 reported as having trouble with moss is in a concrete-lined section 
 where the velocity is stated to be as high as lo ft. per second. 
 
 This moss does not grow rapidly in the shade but is troublesome 
 where the water is clear and exposed to bright sunlight. In some 
 localities cottonwood or other quick-growing trees are planted along 
 the canal in order to provide a shade in the hopes that within two or 
 three years the shadows from the trees wUl be sufficient to practically 
 prevent or to a large extent control the growth of moss. 
 
 Mowing machines to be drawn through the canal by horses walking 
 either in the water or on the banks have been devised. These cut 
 the aquatic plants while the canal is full of water or in operation 
 and as the material rises and floats away, it is caught and pulled 
 out upon the bank. Heavy chains are also drawn along the canal 
 bottom tearing loose the plants or in some instances a metal band 
 with teeth or "moss saw" is used to cut or tear the aquatic growth. 
 Wherever it is practicable to rotate or alternate in the use of water. 
 
166 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 the canal bed is left dry a few days, so that the sun will destroy the 
 weeds; but on the main canal this is not possible. 
 
 The vegetable growth in irrigating canals include many species of 
 algae representing such genera as Spirogyra, Stichococcus; Micro- 
 spora, Ulothrix, etc., occurring in flowing water of canals. In still 
 water these may usually be eradicated with little or no difficulty by 
 the application of a small quantity of copper sulphate. The 
 different species vary greatly in their susceptibility to this poison; 
 some species are readily killed by an exposure of two to four hours 
 to a solution of one part of copper sulphate to twenty million parts 
 of water, while others resist for several hours a concentration of one 
 part of copper sulphate to one million parts of water. In addition 
 to these susceptible algae other plants such as Potamogeton, Chara, 
 etc., sometimes appear in canals, and are too resistant to the action 
 of chemical agents to be eradicated by such means. 
 
 Organization for Operation and Maintenance. — The organization 
 for operation and maintenance depends largely upon the size of the 
 system and its complications. A small system can be operated by 
 a very few men, as is the case with a small railroad, where it makes 
 little difference whether absolute accuracy as to time and service is 
 observed. With the large irrigation system, however, embracing 
 thousands of farms, where every small error in judgment may result in 
 losses to hundreds of individuals, far greater care proportionally must 
 be given to a system, and the expense is correspondingly increased, 
 the organization being more highly specialized and adapted to the 
 greater demands made upon it. 
 
 The object of this organization, and in fact of the whole works, 
 is to deliver water promptly and in necessary quantities. Reliable 
 service is of the highest importance — far more than cheapness of 
 operation. With good management the crop returns are so large, 
 and with poor management so disappointing, that the irrigators 
 have less concern about the cost than they have about the efficiency. 
 
 At the head of the organization must necessarily be the manager, 
 who must oversee the general system, decide all questions in ac- 
 cordance with the laws and regulations, and settle the innumerable 
 controversies which are inseparable with delivery of water through 
 open channels. Under the project manager are usually two or 
 more superintendents, who in turn have oversight of a sufficient 
 number of water masters or canal riders to enable the entire sys- 
 tem, including hundreds of miles of main and branch canals to be 
 traversed once or twice each day. 
 
OPERATION AND MAINTENANCE 167 
 
 In an irrigation project with farms of ordinary size the irrigated 
 acreage in each being from 40 to 60 acres or more, one canal rider 
 is required for about 3,000 acres. If every delivery is to be visited 
 each day the number of canal riders will be materially increased 
 and in case the holdings of 80 or 160 acres each the number can be 
 reduced. 
 
 The wages paid to canal riders generally range from $75 to $80 
 a month and may go as high as $90 or $95. In most cases local men 
 are employed, the more important men being kept throughout 
 the year and the others for six months or during the irrigation 
 season. Each canal rider is required usually to furnish his own 
 horse and has frequent need of an additional animal to allow suitable 
 rest, as the daily average ride is from 20 to 25 miles. The water 
 masters are paid usually I125 to $150 a month and supervise eight 
 or ten or more canal riders. There is also a clerical force the size 
 of which is dependent upon the detail with which the records are 
 kept. 
 
 Records. — Accurate records are as essential in the proper operation 
 and maintenance of a system of water supply as they are in other 
 business. Without them there is continual uncertainty with 
 resulting controversies, and although it is not possible to settle all 
 claims by reference to the records, yet most of these are quickly 
 adjusted by having the facts correctly stated. The principal 
 records are those which show the amount of water entering and 
 leaving the reservoirs day by day, the dates, and quantities taken 
 into the canals and distributed to each branch or lateral, and finally 
 turned to each wateruser. These records give by comparison 
 the losses by evaporation and seepage, call attention to possible 
 thefts of water, and form a guide by which the manager from day 
 to day controls the system. 
 
 In addition to the water measurements, it is necessary to have 
 records of acreage and of crops — these being revised at the beginning 
 and end of each crop season in order to obtain data concerning 
 the use of water, and prevent unlawful diversion from one field to 
 another. 
 
 Costs. — There are few reliable figures of cost of operation and 
 maintenance, this being due largely to the fact that there have 
 been no general agreements as to the character of items which 
 are to be included in this. As a rule it may be said that the small 
 systems operated by the farmers apparently cost them from 50 
 cents to 75 cents per acre per annum, and sometimes less; but it is 
 
168 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 not possible to ascertain whether all of the overhead charges 
 have been included in this, as much of the work is performed by 
 volunteer services, and is not made a matter of record. The 
 larger systems where better records are kept apparently cost 
 from $1 to $1.50 per acre for operation and maintenance, not 
 including in this the depreciation or cost of larger repairs due to 
 catastrophies. 
 
 As a rule it may be stated that the less the cost, the poorer the 
 results, and the larger the losses on the crop returns. For every 
 10 cents per acre saved in the apparent cost of operation and mainte- 
 nance, the ultimate crop production may have been reduced from 
 $1 to $10. 
 
 In examining the history of many of the private enterprises, it is 
 extraordinary to see how, through neglect or by false economy, 
 water has been kept out of the canal during critical times of the 
 year, with resulting crop losses aggregating tens of thousands of 
 dollars, these being regarded by the farmers as dispensations of 
 Providence rather than as a result of their own ignorance or lack 
 of organization. It has been no uncommon thing for a large canal 
 to be deprived of water for a week or ten days during the extreme 
 heat of summer, and the crops on 10,000 acres reduced in value 
 by at least $5 per acre — this loss resulting simply from an endeavor 
 to save a few hundred dollars in the management. 
 
 In keeping records of cost, the first or most obvious classification is 
 under the two heads of "operation" and "maintenance." It is 
 necessary to distinguish somewhat arbitrarily between these as one 
 merges into the other. There is also a third class of items, which is 
 sometimes considered, namely, betterments, which really belongs in 
 part in the original construction cost, but which being incurred after 
 the canal system is practically finished, must be carried as a part of 
 the maintenance or upkeep. 
 
 The operation costs are usually considered as including those items 
 which pertain to the distribution of water to the individual farmers, as 
 distinguished from the maintenance which relates to the expenditures 
 having to do with the preservation of the system. 
 
 Each of these two classes of expenditure may further be divided 
 into the principal features of which a canal system consists, namely, 
 -first, storage or reservoir division; second, the diversion dam and head- 
 works; and third, the main or trunk line canal and principal branches; 
 fourth, the lateral or sub-lateral system leading from the larger 
 branches to the individual farms. 
 
OPERATION AND MAINTENANCE 169 
 
 In turn again, these items consist of expenditures for supervision, 
 labor, materials, supplies, etc. Thus carried to the extreme, the 
 cost-keeping system should show the expenditures, for example, in 
 labor or materials in operating the diversion dam and headworks, or 
 in maintaining the main canal. 
 
CHAPTER X 
 STORAGE WORKS 
 
 Determination of Storage Supply. — ^The question of storage must 
 be considered sooner or later by the engineers of any considerable 
 irrigation system. It is true that the earlier canals taking water from 
 perennial streams, and having first rights to the natural flow, may 
 have adequate supply for most of their lands, but as the country 
 develops even these canals may be extended or enlarged. The 
 extent to which this can be done depends upon acquiring additional 
 waters, since the rights to water for new lands is secondary to those of 
 lands which have been previously irrigated. Thus it is that the 
 matter of conservation of the floods, and of the waters which occur 
 at periods of the year when not needed for irrigation becomes very 
 important. 
 
 In attempting to arrive at a determination of the storage supply, 
 there are several factors which must be taken into account. The first 
 question is relative to the total quantity of imappropriated waters, 
 and the second has to deal with the character and capacity of reser- 
 voirs feasible to construct within reasonable Hmits of cost. It is 
 necessary to consider also whether the floods occur at such times 
 and in such a manner that they can be controlled. 
 
 In every case the question of probable cost is important, and in- 
 volves taking into account the quantity of water required for the 
 lands under consideration; the latter is governed largely by the char- 
 acter and location of lands, as well as the area to be watered. 
 
 In practically every case engineering and economic questions are 
 involved, the former dealing with the physical conditions of runoff 
 and topography, the latter, with cost of conserving and value of the 
 supply. 
 
 Annual Runoff. — Of the engineering questions involved in storage, 
 the first and most quickly answered, if measurements of the stream 
 are available, is as to the annual runoff, or total quantity of water 
 which has occurred in the stream each year in the recent past. It is 
 obvious that this quantity limits all future development, unless the 
 drainage area can be increased by bringing into it one or more streams 
 from another basin. The annual runoff varies largely from year to 
 
 170 
 
STORAGE WORKS 171 
 
 year, and in any one year may be several times that of a measured 
 year, or it may be far less. 
 
 There are also to be found, in studying measurements of runoflf for 
 consecutive years, that in some one year there were practically no 
 floods, and that such a year may be preceded, or succeeded by a 
 season of drought, as dry years frequently occur in succession. 
 There are also to be expected other years when the floods surpass 
 those in the memory of the oldest inhabitant, and when structures 
 which were planned to meet ordinary conditions may be swept away. 
 In other words, all proposed works for storage must be considered 
 with a view to the fact that they must meet extraordinary flood con- 
 ditions, and may occasionally not receive much, if any, water for 
 storage. 
 
 There have been in the past many efforts to find some simple rule 
 connecting the amount of rainfall as measured on the drainage 
 basin with the quantity of water flowing from it. Some engineers 
 have assumed that the runoff would be a trifle less than one-third of 
 the rainfall. The attempt to apply such a rule, however, under 
 different topographic and climatic conditions, has led to absurd 
 results, as in the arid west, the runoff may not exceed 2 or 3 per cent, 
 of the rainfall as measured on the higher portions of the catchment 
 area. The runoff in any one year, especially that of unusual rainfall 
 may rise to 10 or 12 per cent, over the entire watershed, or in a year 
 of drought drop to less than i per cent. (For further discussion see 
 chapter on Water Supply.) 
 
 Amount of Rtmoff that can be Stored. — Not all of the water 
 shown by the measurements of river flow is available for storage. 
 The records of river flow usually show that a certain quantity of 
 water has passed a given point on a stream during certain seasons of 
 preceding years. It is frequently assumed that all the water can be 
 held, and many unwise investments have been made because of the 
 fact that extensive works have been constructed, based upon the 
 assumption that all the water known to occur in the recorded floods 
 could be held in storage basins. 
 
 The limitations upon the amount of water which can be econom- 
 ically stored are those arising from two causes; first, geographical, or 
 topographical; and second, hydrographic. Under the first are 
 included those which pertain to the relative position on the drainage 
 area of the storage basins. The best of these are usually found 
 relatively high up on the stream or on its tributaries, and in such 
 positions that the amount of flood water occurring above the dam site 
 
172 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 is relatively small. In other words, the greatest floods occur at points 
 below those at which feasible storage sites are found. It may be 
 said to be a general rule that the better the physical conditions for a 
 reservoir site, the less the amount of water available at that point. 
 In nature we frequently find broad valleys with relatively narrow out- 
 lets through which flow insignificant streams, with small, or irregular 
 floods; and, on the other hand are large streams with considerable 
 volume flowing through narrow, deep valleys, with fall so great that 
 storage reservoirs are out of the question. 
 
 These hydrographic conditions limiting storage are those which 
 arise in accordance with the volume and rapidity or intensity of the 
 flood and in the manner in which one flood may follow another in 
 immediate succession. If a large reservoir is located on the main 
 stream, it will, of course, catch all of the flood coming into it up to the 
 capacity of the reservoir; but if, as is occasionally the case, the 
 storage reservoir is on a side stream, and the floods in the main stream 
 must be diverted by a flood water canal, then the amount of water 
 which can be brought into such a reservoir is limited largely by the 
 capacity of this flood canal. If the floods occur somewhat slowly, 
 and do not exceed the capacity of this diversion canal, the maximum 
 amount can be stored; but, if the flood is flashy, with a high peak 
 exceeding the capacity of the canal, then a correspondingly less 
 amount can be conserved. 
 
 It frequently happens that droughts succeed droughts, and floods 
 follow floods, but in operating reservoirs, it is usually assumed that 
 the first flood will be caught, and held to the full extent. If, then, 
 there happens to be a second flood following upon the first, while the 
 reservoir is still full, and before it can be drawn down for storage 
 elsewhere, or for beneficial use, then it follows that the second flood 
 is largely wasted. Thus it happens that although on casual inspec- 
 tion of the data of river flow there appears to be a large volume of 
 water, yet careful study of the limitations frequently lead to dis- 
 appointing results, because of the fact that only a small portion of 
 the total amount of water can be economically held. 
 
 Each stream or catchment area must be studied by itself, with 
 referehce to the location and capacity of the proposed storage sites, 
 and of the relation of these to the particular part of the drainage 
 area tributary to each storage basin. The prior appropriations, or 
 legal claims to flood water, which may exist, and the rapidity of the 
 occurrence of floods, must also be studied carefully with reference 
 to these particular sites. As a result it is frequently necessary to 
 
STORAGE WORKS 173 
 
 exclude from consideration large and important parts of a drainage 
 basin because of the fact that these parts are not tributary to any 
 economical reservoir site. 
 
 Ordinarily it may be said that the building of a reservoir of 
 sufficient capacity to hold all of the flood waters from a given shed 
 is impracticable, both from a physical and economic viewpoint. 
 It consequently becomes a question of determining the greatest 
 amount which can be economically held. To do this, it is sometimes 
 necessary to consider carefully the future need for water and its 
 probable value. 
 
 Seepage Losses. — The full or theoretical capacity of any reservoir 
 is not always the amount which can be depended upon for beneficial 
 use. There are certain losses which must be taken into account, 
 and occasionally some gains. The principal losses are grouped 
 under the headings (i) Evaporation, and (2) Seepage. 
 
 The evaporation losses are practically continuous and so far as 
 present knowledge goes, cannot be controlled at reasonable cost. 
 If it were practicable to cover the reservoir to exclude sunlight 
 and wind movement, they could be reduced to a minimum, but the 
 necessary expenditure for this purpose would be prohibitive. In 
 cases where the spring floods are held in a reservoir and the water 
 is drawn down during the succeeding summer, these losses are 
 usually not very serious. Under these conditions there are only 
 three or four months of evaporation to consider, but if the reservoir 
 is to carry water over to years of drought, then the total annual 
 losses come into play and these usually form a large proportion 
 of the amount stored. 
 
 The seepage losses are frequently matters of great concern but 
 unUke the losses of evaporation there is a tendency for these to 
 gradually reduce by the lapse of time due to the silting up of the 
 bed of the reservoir. In new construction, where water is being 
 held for the first time in basins which have not been thoroughly 
 wet for centuries, the seepage losses are very great. Each year 
 as the reservoir is filled higher and higher and newer lands are sub- 
 merged, these losses continue, but as the underlying soil becomes 
 packed through the presence of water and layers of fine silt are 
 deposited on the bottom, there is a tendency to render the under- 
 lying earth less pervious and to prevent the free escape of the water. 
 
 The accompanying diagrams illustrate some of these conditions 
 of losses of water from recently built storage works. They are 
 especially instructive as showing the actual conditions. In these 
 
174 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 CLEAR LAKE BESEBVOIB - OiLIPOKNIA 1911 
 
 Feb. I V.O.T. I Apr. ] May | June | July 1 Aug. | Sept. [ Oct. 
 
 Fig. 37. — Diagram illustrating losses in reservoirs. 
 
STORAGE WORKS 175 
 
 comparison is made between several reservoirs of distinctly different 
 geologic structure; for example the East Park Reservoir in the 
 Orland project, California, is in a basin in crystalline rocks in the 
 mountains where the seepage losses are probably at a minimum, 
 while the other reservoirs noted are in a region of lava flow. In 
 the case of the East Park Reservoir evaporation may account for 
 most of the water which disappears. In comparison with this is 
 to be noted the Cold Springs Reservoir of the Umatilla project, 
 Oregon, which is in a basin cut in eruptive rocks of large porosity, 
 these being overlaid with somewhat heavy beds of sands, gravel, 
 and wind-deposited materials. Still larger losses are shown in 
 the Clear Lake Reservoir of the Klamath project, Oregon-Cali- 
 fornia. This has been built partly for the purpose of reducing 
 the floods in Lost River and where the seepage losses into the under- 
 lying lava were anticipated as being large. Greater losses are 
 shown from the Deerflat Reservoir in Boise project, Idaho, where 
 water storage is provided out on the rolling plains and where the 
 lava is covered with a relatively thin layer of soU, these seepage 
 losses are being steadily reduced year by year but wQl probably 
 always form a notable percentage of the amount of water stored. 
 
 Evaporation Losses. — Every body of water, large or small, 
 exposed to the sun and wind, is constantly losing from the surface 
 a greater or less amount, which is dependent mainly upon the 
 temperature and wind movement, and to a less extent upon other 
 causes — such, for example, as altitude and atmospheric conditions 
 as regards moisture. In the case of natural reservoirs, spread over 
 hundreds of acres, with exposure to winds which sweep down the 
 mountain, and with a hot sun pouring from a cloudless sky, the 
 losses are very great, and become a notable percentage of the quan- 
 tity stored. These losses have been the subject of prolonged study 
 by various observers — notably those of the Weather Bureau, and 
 officials in charge of important city waterworks. 
 
 As yet the laws governing evaporation in large bodies of water are 
 not fully understood, nor reduced to exact statements. For the 
 present the engineer must base his assumptions upon the more or less 
 empirical formulae, or arrive at them from direct comparison with 
 observations of the rate of evaporation under similar conditions of 
 climate and topography. 
 
 The evaporation during the summer season with its higher tempera- 
 ture is, of course, greater than during the winter, although there is 
 an appreciable loss during the cold weather, even from the frozen 
 
176 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 surface of the lake. The losses from the surface of a broad shallow 
 basin are also greater than those of a deep body of water, because 
 of the higher temperature of the shallow waters. The wind movement 
 also has a very important effect, in that it carries away the moisture- 
 laden air immediately over the surface, and permits a more rapid rate 
 of change from liquid to vapor. 
 
 The following table illustrates the difference in rate of evaporation 
 month by month, under different local and climatic conditions. It is 
 given merely as an illustration, and as demonstrating that the loss 
 by evaporation is large : 
 
 DEPTH OF EVAPORATION IN INCHES, BY MONTHS 
 
 Month 
 
 Neb. 
 
 Idaho 
 
 Oregon 
 
 Lake 
 Tahoe 
 
 Nevada 
 
 Wash. 
 
 N. Mex. 
 
 Arizona 
 
 Jan. . . 
 
 Feb.. 
 
 Mar. 
 
 Apr. . 
 
 May. 
 
 June. 
 
 July. 
 
 Aug.. 
 
 Sept. 
 
 Oct.. 
 
 Nov. 
 
 Dec. 
 
 I -75 
 1-75 
 300 
 4-SO 
 6.25 
 8.0s 
 IO-9S 
 9-39 
 7-44 
 SS9 
 4.00 
 3.00 
 
 I -SO 
 
 2.2s 
 
 4.00 
 
 7.2S 
 
 10.68 
 
 II. OS 
 
 II. 15 
 
 11.77 
 
 9-7S 
 
 S-40 
 
 2.70 
 
 I -5° 
 
 0.50 
 
 ■I. 25 
 
 3-27 
 6.64 
 7-iS 
 6.99 
 8.01 
 9. 21 
 6.13 
 2.50 
 1 .00 
 0.50 
 
 I.7S 
 I-7S 
 I -75 
 2.00 
 3.00 
 S.oo 
 6.49 
 7.42 
 7.75 
 4-33 
 3-13 
 2.25 
 
 75 
 7S 
 
 2S 
 2S 
 25 
 
 7.86 
 9.86 
 8.70 
 513 
 
 3-35 
 2.50 
 2.00 
 
 1-75 
 2.50 
 6.25 
 7.91 
 8.36 
 8.90 
 10.74 
 9.41 
 
 3-iS 
 2.00 
 
 2.50 
 
 2.75 
 
 450 
 
 8.00 
 
 11.50 
 
 13-45 
 
 11-57 
 
 10.48 
 
 8.58 
 
 6.76 
 
 3-86 
 
 3.00 
 
 4-59 
 
 4-75 
 
 6.25 
 
 9.00 
 
 11.50 
 
 13-50 
 
 14-25 
 
 14.23 
 
 13.76 
 
 II. 31 
 
 7-39 
 
 4-65 
 
 Totals 65.67 
 
 79.60 
 
 53-45 
 
 42.21 
 
 53.65 
 
 67.96 
 
 86.95 
 
 115-18 
 
 The above figures of depth of evaporation are probably the results 
 of observation by Professor Frank Bigelow of the U. S. Weather 
 Bureau (Engineering News, Vol. 63, p. 694, June 16, 1910). Many 
 of the figures are interpolations, but they represent the results of ob- 
 servations of evaporation — not from reservoirs, but from pans, 
 usually 4 ft. in diameter, located on the ground. The losses from a 
 large body of water may be more, but presumably are less. Ob- 
 servations indicate that there is a nearly uniform rate of evaporation 
 over the area of the water surface of a lake or pond, beginning at a 
 short distance from the shore. 
 
 It should be kept clearly in mind that these figures, and similar 
 figures frequently quoted, represent the losses from relatively small 
 
STORAGE WORKS 177 
 
 areas, and not from the lake surface itself. There is a very great 
 difference in the amount of evaporation from pans placed side by 
 side, depending upon their diameter and height of rim of the pan 
 above the surface of the water ; and there is no known relation between 
 the evaporation from a pan of a given size and an open body of water; 
 the losses in each case may be greater or less, dependent upon many 
 conditions. 
 
 In looking over these figures, it is to be noted that although the 
 total evaporation for the year may be approximately the same for 
 difiEerent localities, the distribution of this by months is variable, 
 dependent upon climatic conditions prevailing at the time. For 
 example, in Oregon observations of winter evaporations show a 
 remarkably low loss as compared with the others. All show a maxi- 
 mum in July or August, the rate of evaporation dropping off rapidly 
 after these months. 
 
 The effect of evaporation in reducing available storage capacity 
 will depend upon the size and depth of the reservoir, and also the 
 length of time that water must be held in storage; that is to say, the 
 percentage of loss from a large, shallow reservoir is far greater than 
 from a small but deep one of equal capacity; also, the relative loss 
 from a storage supply held during a single irrigation season will be 
 far less than if water must be held over from one year to the next. 
 The losses by evaporation of 6 in. in depth during a month of 
 thirty days, on a reservoir having a surface area of 3,000 acres is 
 equivalent to a steady flow throughout the thirty days, of approxi- 
 mately 25 second-feet. 
 
 Ratio of Runoff to the Storage Capacity. — The relation which 
 the total runoff or amount of water delivered from a given drainage 
 basin bears to the storage possibiHties is one of the first objects of 
 concern to the engineer interested in the conservation and develop- 
 ment of a water supply. As a rule it may be stated that the larger 
 the runoff per square mile drained, the less the probabilities of 
 finding good storage sites. This is because of the fact that with 
 large runoff the streams through past ages have eroded their channels 
 and have carved broad outlets through various obstructions, making 
 it difficult to create artificial basins. On the other hand, with 
 reduced runoff per square mile, the streams have become over- 
 loaded with sand and gravel; their beds are now choked and they 
 have not been able to cut such outlets in the natural barriers. This 
 general rule is, of course, modified by geologic conditions, especially 
 where ancient glaciers have built morains across the valleys, or 
 
178 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 where there has been the tilting of the earth's crust in one direction 
 or another, changing the former slopes and bringing in new 
 complications. 
 
 The amount of total runofiF is a quantity which cannot be modified 
 appreciably by man. It varies from year to year according to the 
 climatic oscillations. The portion of this which may be put to 
 beneficial use is, however, dependent quite largely upon human 
 agencies. It is assumed to be practicable to begin systematic 
 forest protection at the head-waters, and thus exercise a beneficial 
 influence upon the way in which the runoff comes from the steep 
 slopes. It is now generally believed to be essential to the full 
 conservation of the water supply that the catchment areas of the 
 streams be studied and controlled with reference to the covering 
 of trees, shrubs, grass, etc. Assuming that this is done, and that 
 the violence of extreme floods, or the rapidity of runoff is modified 
 as far as practicable by good forest and grazing conditions, then the 
 question next in order is that of proportion of the water flowing 
 in the stream which can be controlled. 
 
 On most streams within the irrigated region, the ordinary summer 
 flow has already been appropriated and put to beneficial use. Canals 
 have been built with capacity sufficient to take all of the normal 
 flow during the crop season. Assuming that this is the case, the 
 next question is with reference to the waters which occur in the 
 stream at times other than during the crop season, and also of the 
 floods which take place in the spring or early summer, and which 
 exceed in volume the capacity of the canals already built. 
 
 All of the water which flows before and after the crop season, 
 or at the times when not actually needed for irrigation during the 
 season, should be held for use later, and under ordinary conditions 
 it may be considered as available for storage. However, there 
 has recently grown up a practice which has resulted in some doubts 
 and legal controversies. Some of the oldest appropriators are 
 attempting to use the fall and winter waters for flooding the farming 
 lands after the crops are removed, with the idea of saturating these 
 lands as far as possible, in order to reduce the amount of water 
 needed during the succeeding crop season. There are a few con- 
 ditions of soil and climate where this can be done effectively, but 
 there is always a question as to whether this is not a wasteful use 
 of water. In the case of heavy, or loose gravels underlying the 
 soil, it appears probable that even though these gravels are filled 
 with water during the fall and winter, yet before spring they will 
 
STORAGE WORKS 179 
 
 drain out and the benefits derived will not be comparable with the 
 resulting waste. Because of this condition, conflicts have arisen 
 between the reservoir men on the one hand claiming that they are 
 entitled to this water out of the crop season, and the farmers on the 
 other, who claim that they are entitled under their appropriations 
 to all the water they desire to use throughout the year, and that they 
 should be permitted to store it in the ground in the manner described. 
 
 Regarding the floods, there has been no serious question as to 
 the fact that the portion of these in excess of the capacity of the 
 irrigating canals should be stored. These floods usually occur 
 at the beginning of the crop season, and hence the length of time 
 during which they are stored and the consequent losses by evapora- 
 tion, are at the minimum. 
 
 Determination of Storage Required. — Having ascertained the 
 limitation of the possible storage set by physical conditions, such as 
 quantity of water, and capacity of feasible storage basins, the suc- 
 ceeding questions are generally easUy answered, because it is usually 
 assumed that the entire available quantity, extreme flood excepted, 
 will be held for future use. It occasionally happens, however, that 
 the area of irrigable land which can be reached from any one storage 
 reservoir, or system of reservoirs is limited, and in that case the 
 question is narrowed to the actual needs of this particular tract of 
 land. It is, of course, not economical to go to the extreme of pro- 
 viding more storage than is actually needed, and on the other hand the 
 possible crop losses will not justify providing inadequate storage. 
 
 Theoretically, the storage reservoir should be of such capacity that 
 it can be drawn upon whenever needed to supplement the ordinary 
 supply received from the unregulated flow of the stream. Nearly 
 every irrigable tract is enabled to obtain water from a perennial or 
 intermittent stream, flowing during the early part of the crop sea- 
 son and the storage reservoir is intended to supplement this sup- 
 ply. In some cases, however, this is so irregular that the storage 
 reservoir must be large enough to take care of the entire tract. 
 
 The first question, therefore, is: What dependence, if any, should 
 be placed upon the natural flow? This varies greatly from year to 
 year, and in any period of ten or twenty years there is some one year 
 which is much lower than all the rest. Under the existing crop con- 
 ditions, is it economical to make provision to take care of this 
 exceptionally low year, or will the expense of so doing not justify the 
 results? In other words, is it not better to figure on reduced crop 
 production during this one year than to make extraordinary provision 
 
180 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 for it? In such case, knowing in advance that there may not be 
 enough water, the farmers are warned to economize the water in 
 saving the trees, and to take their risks upon the least valuable of 
 the annual crops. This question of economical importance of crop 
 failure one or more years in every ten must be balanced against the 
 probable cost and practicability of providing against the exceptional 
 year. 
 
 Having made certain assumptions as to the requirements of mini- 
 mum years, there then follows the assumption as to the amount of 
 water which can be depended upon by natural flow, if any, during 
 these years, and the amount which must be stored to provide the 
 supplemental supply. The assiimptions of minimum year require- 
 ments will, of course, vary under different conditions of climate and 
 character of crops to be raised. Under certain conditions, it may be 
 assumed that for one year in ten, or twenty, it will not be econom- 
 ically possible to provide a complete supply. This may be justified 
 by the fact that the losses during that one year will be more than 
 balanced by the saving in the cost of storage works. 
 
 This minimum flow does not occur throughout the crop season, but 
 for certain months, or portions of months; and for the other months 
 it is not necessary to provide the same amount of storage. That is 
 to say, from day to day there wUl be a greater or less quantity of 
 water available from the stream, and there will be a greater or less 
 demand for this, according to the needs of the crops. The difference 
 between the probable amount which can be had from the stream, 
 and the probable regular demands from the farmers, measures the 
 quantity which should be available in the reservoir. 
 
 The sum total, however, of these daily demands upon the reser- 
 voir do not by any means measure the storage required. This must 
 be increased to meet losses: 
 
 (a) by evaporation which is dependent upon length of time 
 stored and climatic conditions; 
 
 (b) seepage in the reservoir itself; 
 
 (c) losses of water in transit from the reservoir to the lands; 
 
 (d) other losses, often unaccountable, mainly due to improper 
 methods of handling and distribution. 
 
 The storage capacity also is modified by the fact that there is more 
 or less accumulation in the reservoir due to irregular storms, at the 
 same time that these losses are occurring, so that we have a constantly 
 fluctuating burden to be carried by the reservoir. 
 
STORAGE WORKS 181 
 
 The amount of storage required, as is obvious from the preceding 
 statements is not a simple matter directly comparable with the acry- 
 age to be served; first, because this acreage may be supplied in part be 
 a fluctuating flow of the stream; and, second, because its require- 
 ments for water vary from day to day. As far as practicable, a 
 schedule should be made in advance of the probable needs of the land, 
 depending upon the character of crop, and the time of year when the 
 various crops require certain amounts of water. If most of the 
 fields are in alfalfa, this will require water at intervals of two or three 
 weeks throughout the entire growing season, or even late in the fall; 
 whereas, if more of the land is in wheat or smaller grain, and this is 
 not followed by another crop, the irrigation may be finished early in 
 the summer, and largely by waters taken directly from the river. 
 
 In considering the question of storage, therefore, it is necessary to 
 assume what are, or will be, the principal crops of a region, and the 
 time of year when these will probably be irrigated. In other words, 
 make certain assumptions as to the total amount of water which 
 should be delivered day by day. From this is to be deducted the 
 probable amount which may be obtained without regulation from 
 the natural flow of the stream, including floods. The difference rep- 
 resents the deficiency which should be supplied by storage on the 
 given days or periods of time, and a study of these probable daily 
 demands will show that the reservoir need not be planned with ref- 
 erence to the entire amount of water which will be used during the 
 year, but rather with reference to a fluctuating quantity. The 
 problem thus is not one of simply ascertaining the details for the year 
 of river flow, and of water to be applied to the land; but, on the con- 
 trary, that of an analysis, day by day, of the varying quantities — 
 each modified by climatic conditions as regards supply and probable 
 crop conditions, as regards needs of water. 
 
 Economic Questions in Storage. — Water storage for irrigation is 
 relatively a new subject as regards the economic considerations. 
 Irrigation itself is as old as civilization, and the questions of canal 
 construction and the diversion of the water to the land by gravity 
 are fairly well understood. Water storage for agriculture also has 
 been practised to a certain extent, especially in India, but there has 
 not yet been developed a consistent theory, or set of rules, based 
 upon economic considerations. Each case of storage has been con- 
 sidered by itself with reference to local conditions, probable amount 
 of money available for expenditure, the works being built accordingly 
 and then modified on the basis of further experience. 
 
182 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 Theoretically, water conservation by storage should be extended 
 to a fuU limit of the amount of water which occurs in nature. As a 
 rule there is more good land needing water than there is water to 
 supply it; and wherever this holds true, it would seem to follow that 
 every drop of water should be held to irrigate the lands. There 
 comes in here, however, the question of cost. To take an extreme 
 case, there will be in a given period of twenty years one excessive 
 flood. The waters of this flood cannot be held indefinitely in a basin, 
 because they will escape by evaporation. Even if any considerable 
 part could be held, the question arises as to whether the cost of pro- 
 viding a large enough basin would be justified by the value of the 
 Waters, coming, say once in twenty years. The agricultural develop- 
 ment of the country could not be economically adjusted to utilize 
 this irregular supply, especially as the time of occurrence could not be 
 known in advance. In short, by considering an extreme case, it is 
 recognized that there are few conditions where all of the flood waters 
 can be economically held. We must, therefore, figure on holding less 
 than the total flow, especially in the extremely wet years. 
 
 Coming down the scale from the excessive floods, we finally reach 
 a place where it becomes an evenly balanced matter of cost and 
 benefits; that is to say, the floods which occur every year, or four 
 years out of five, should undoubtedly be saved, if possible, because 
 for the fifth, or dry year, some water may be held over, or the area of 
 annual crops can be reduced. Starting from the other extreme, it 
 may be also said that storage should not be neglected, because there 
 are known to occur certain years, once in ten or twenty, when there 
 are practically no floods. It would be unwise to assume that because 
 such a year occasionally occurs, therefore, no storage should be 
 provided. 
 
 We thus have an intermediate point somewhere between these 
 two extremes — namely, that storage in general should not be con- 
 sidered for extreme floods; nor should it be limited to the minimum 
 flood. 
 
 A determination of this intermediate point rests upon crop values 
 immediate or prospective. If the climate is cold and the principal 
 crops are such as to bring but low returns per acre, then there is 
 little justification in making a large expenditure for the storage, 
 such as would be practicable and desirable in warmer climates, 
 where crop follows crop in rapid succession and where the unit 
 value per acre of crops is large. 
 
 The immediate, or present value of the crops produced in an area 
 
STORAGE WORKS 183 
 
 should not be used as the limiting feature, because it is proper to 
 assume that with more complete development of the area, there will 
 result larger crop production, and better facilities for marketing 
 and handling this. It is also safe to assume that ordinarily when 
 the country is developed, there can be no over-production in the 
 sense that such large quantities of crops will be produced that the 
 value will decrease. This condition may exist temporarily, but 
 with irrigated lands forming such a small percentage of the arid 
 west, this condition cannot be permanent; hence, it is desirable 
 to use a reasonable optimism with regard to future crop values, 
 basing these not upon the temporary conditions of extremely high or 
 low values, but upon those which may be considered more nearly 
 normal. 
 
 Cost of Storage. — From what has been stated before, it is apparent 
 that in this, as in other operations, the determining factor in water 
 storage is cost; both absolute, as dependent upon the amount of 
 money available, and relative, as regards the benefits which may 
 be derived. To illustrate this point, we may consider two extreme 
 cases: If the area under consideration is capable of high develop- 
 ment, or is practically suburban in character, with genial climate, 
 such as that of the State of California, the conditions approach 
 those of water storage for a city where almost any amount of money 
 can be expended, the cost of storage of $ioo per acre-foot may not 
 be beyond consideration. 
 
 On the other extreme, where the lands to be supplied are mainly 
 used for forage crops, the cost of storage of $s per acre-foot may give 
 rise to hesitation. Between these two there is a wide range of 
 amounts which may be considered. The following table gives 
 some costs which have actually been incurred. In arriving at these 
 the total capacity of the reservoir is taken, irrespective of the fact 
 as to whether this is filled each year, or whether it is increased by 
 serving as a temporary or regulating reservoir, as for the present 
 purposes, it is assumed that each reservoir has been built to its 
 maximum feasible capacity. 
 
184 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 COST OF RESERVOIRS COMPLETED BY UNITED STATES RECLAMATION 
 SERVICE, DECEMBER 31. ipn 
 
 State 
 
 Name of 
 reservoir 
 
 Available' 
 capacity 
 
 Cost to December 31, 
 1911 
 
 Total 
 
 Per acre- 
 foot 
 
 Arizona 
 
 Roosevelt. 
 
 1,284,000 
 
 462,000 
 
 45, 600 
 
 173,000 
 
 150,000 
 
 40,000 
 
 50,000 
 
 203,770 
 
 13,000 
 
 34,000 
 
 1,025,000 
 
 456,000 
 
 380,000 
 
 13,746,696.41 
 127,408.61 
 264,929.66 
 904,542 . 68 
 569,278.86 
 154,019.19 
 442,786.10 
 
 1,242,438.77 
 
 328,169.26 
 
 429,121.13 
 
 1,739,675.81 
 
 I,i9i>734.2i 
 
 441,023.04 
 
 $2.92 
 
 California 
 
 
 .28 
 
 California . . 
 
 East Park . 
 
 5.82 
 
 Idaho. . . 
 
 Deer Flat 
 
 5. 22 
 
 Idaho 
 
 LakeWalcott 
 
 3.80 
 
 New Mexico 
 
 3.86 
 
 Oregon 
 
 Cold Springs 
 
 Belle Fourche 
 
 3 84 
 
 S. Dakota 
 
 6.12 
 
 Washington 
 
 Washington 
 
 2.52 
 
 Bumping Lake 
 
 Pathfinder. . 
 
 12.60 
 
 Wyoming. . . 
 
 1.70 
 
 Wyoming 
 
 Shoshone 
 
 2.62 
 
 Wyoming 
 
 Snake R. Storage. . . 
 
 1. 16 
 
 
 
 Grand totals 
 
 
 4,316,370 
 
 $11,582,649.21 
 
 Average 
 2.70 
 
 
 
 
 ' Acre-feet. 
 
CHAPTER XI 
 RESERVOIR SITES 
 
 General Requirements. — A good reservoir site, from a purely- 
 topographic standpoint, may be considered as one where a broad 
 valley or expansion may be permanently closed by a dam of reason- 
 able dimensions. In order, however, that such a site may have 
 value for storage purposes, a water supply is also necessary. In 
 his search for a reservoir site the engineer must, therefore, confine 
 his attention to the valleys of streams of undoubted water supply, 
 or to near-by valleys into which such streams may be diverted. 
 
 The capacity of a reservoir which may be formed at a given site, 
 compared with the mean annual runoff at that point, is also a 
 matter of some importance. It is obvious that to construct a 
 reservoir so large that it would be filled but once in twenty years, 
 or possibly not at all, would involve a useless expenditure. On 
 the other hand, a reservoir so small that it would hold only a portion 
 of each year's runoff would, in general, cost more per unit of capacity 
 than one of larger size. 
 
 The ideal reservoir site is one which can be economically con- 
 structed to a capacity sufficient to hold all of the runoff from its 
 tributary watershed, except that from extraordinary floods which 
 may come once in ten or twenty years, or possibly at less frequent 
 intervals. 
 
 It may sometimes occur that the amount of storage capacity 
 required is limited by the area of irrigable land in the immediate 
 vicinity. What is wanted in this particular case is not the most 
 economical storage for the entire stream's supply, but the most 
 economic for the capacity required. In such cases there are fre- 
 quently a number of sites from which to choose. Even in such 
 cases consideration should be given to possible future developments, 
 and other things being equal, or nearly so, preference given to the 
 reservoir site whose capacity may be increased to meet possible 
 future needs. 
 
 Good reservoir sites Hke good gold mines are scarce, and as in 
 the case of gold mines there are almost innumerable prospects which 
 are popularly supposed to be valuable but which, upon further 
 
 185 
 
186 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 examination, prove to have some fundamental defect. In beginning 
 a reconnaissance of any area, the inhabitants of that region will 
 call attention to the innumerable localities where in their opinion 
 water might be held, but at a glance an experienced engineer will 
 see that usually the capacity of the basin is too small to justify 
 the cost of a dam because the floor of the valley is usually found 
 to slope at such a high angle that little, if any, water covdd be held 
 behind a dam of moderate height. To the uneducated eye the 
 valley may appear to be level. 
 
 Survey of Reservoir Sites. — Before entering upon definite surveys 
 it is necessary that a reconnaissance be made of the entire lower 
 portion of the area or watershed of the stream to ascertain roughly 
 the relative value of the various possibilities. For the purpose of 
 this reconnaissance the very best field man of largest experience 
 is none too good. It is his duty to weigh carefully the apparent 
 advantages and disadvantages of each locality and then recommend 
 definite surveys. As all such surveys involve the employment 
 of a considerable number of men and are quite expensive, it is 
 incumbent upon the man making the reconnaissance to judge 
 accurately and thus avoid as far as possible useless surveys or 
 examinations involving merely negative results. 
 
 After it has been found by careful reconnaissance that the choice 
 of the reservoir sites is narrowed to a relatively few places, then 
 arrangements should be perfected for a careful topographic survey 
 resulting in a contour map of the storage basin. This map should 
 ordinarily be made with sufficient accuracy to determine the capacity 
 of the basin to within 5 per cent. Greater accuracy than this is 
 generally not necessary but in some cases is desirable. 
 
 The map of the reservoir site should be made on a scale of from 
 1,000 ft. to 2,000 ft. to the inch, dependent upon the size of the 
 basin and nature of the topography, the scale being chosen so as to 
 afford reasonable accuracy for each particular case. At the site 
 of the dam, however, where excavation is to be undertaken and where 
 large expenditures are made, it is necessary to have a far more 
 elaborate map than for the rest of the reservoir. Here a scale of 
 from 100 ft. to 400 ft. to the inch is desirable. In Fig. 38 is given 
 a portion of such a map with contour interval of 5 ft. and the final 
 location of the dam with related works sketched upon it. 
 
 These surveys may be made most quickly and economically 
 by means of the plane-table, if the engineer in charge is accustomed 
 to the use of that instrument and can sketch accurately and rapidly. 
 
RESERVOIR SITES 
 
 187 
 
 If a plane-table man and necessary instruments are not readily 
 obtainable, the survey can be made by the slower and more expensive 
 way of running out contours or marking cross-sections and locating 
 these by transit and level and then sketching in the contours from 
 these somewhat accurately determined points. 
 
 Fig. 38. — Portion of topograpliic map of dam site with related works sketched 
 upon it. Strawberry Valley Project, Utah. 
 
 Contour Maps. — The contour maps which result from the various 
 methods of survey should be drawn on a scale as above indicated 
 and should show sufficient detail to enable a thorough study in 
 the office of the essential features. For this purpose the contour 
 interval of the reservoir basin unless this is very large, should be 
 5 ft. and of the dam site should be i or 2 ft. All rock outcrops, 
 especially near the dam site, should be indicated and all cultural 
 features such as roads, buildings and fences clearly shown, together 
 with the character of vegetation and of soil. Information of this 
 kind is needed, not only in connection with the engineering features, 
 but in adjusting claims for damages, rights-of-way or interference 
 with public travel. In fact there is hardly any detail which can be 
 shown on the map but which may be needed in determining the 
 
188 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 value of the reservoir and in making plans for constructing and 
 operating it. 
 
 Computation of Capacities. — ^The capacities of a reservoir site 
 at various elevations of water surface are determined from the 
 contour maps. As a rule the area enclosed by each contour is 
 measured by a planimeter, the results being determined in acres. 
 The mean of the area in acres between any two contours multiplied 
 by the vertical distance in feet between the contours gives approxi- 
 mately the capacity in acre-feet. The mathematical inaccuracy 
 of this method is no greater than that involved in ascertaining the 
 exact area of the water surface at the different elevations. 
 
 In cases where accurate contours have not been drawn but cross- 
 sections run at short intervals the capacity may be determined by 
 taking the mean area of any two sections and multiplying this by the 
 distance between them, the sum of the various elements thus deter- 
 mined being the total capacity. Results obtained by this method 
 are usually in cubic feet which may be reduced to acre-feet by 
 dividing by 43,560. 
 
 At the bottom of the reservoir is frequently a dead space, that is, 
 water below a certain elevation dependent upon the location of the 
 lowest workable gates, is seldom if ever drawn upon. This dead 
 space is in time filled with sediment if the water is muddy. A 
 deduction should be made from the theoretical capacity of the reser- 
 voir, allowing for this unavailable capacity. 
 
 Choice of a Reservoir Site. — It occasionally happens that there is 
 opportunity for choice between different possible sites. As a rule, 
 however, good reservoir sites are so rare that there is only one that 
 is worthy of consideration, but occasionally the choice must lie be- 
 tween those which offer the fewest objections. In making choice, 
 therefore, it is a question of balancing these objections rather than of 
 considering the benefits. The first and usually the determining 
 factor is that of the cost per acre-foot, this cost being not far from 
 $5 in the case of the ordinary successful irrigation reservoir. Next 
 to the first cost is that of maintenance and depreciation, which in 
 turn is determined by the probable life of the reservoir. As a rule 
 the maintenance cost is very low excepting in case of earthen dams, 
 where continual vigilance must be exercised and frequent small 
 repairs to prevent defects developing. 
 
 The question of life of the reservoir or annual depreciation due to 
 its gradual filling up with material washed from the sides is of great 
 importance. A dam constructed in the course of main-drainage 
 
RESERVOIR SITES 189 
 
 channel which receives all of the storm waters with accumulated 
 gravels, sand, mud and debris, must hold behind it practically all of 
 this solid matter. The clearer waters may be drawn down but in 
 time this solid matter will accumulate, and in the course of decades 
 reduce the capacity of the reservoir. On the other hand, if a similar 
 dam is built on a side channel which does not habitually receive the 
 waters from the great storms the reservoir may be filled by a large 
 flood canal from the main stream and this flood canal may be manipu- 
 lated in such a way as to receive the principal parts of the flood waters 
 while rejecting and washing back into the main drainage all of the 
 gravel and sand, and most of the mud. 
 
 Shallow and Deep Reservoirs. — There is sometimes opportunity 
 for choice between two possible reservoir sites based upon the rela- 
 tive surface exposure as compared with the depth of watei. The 
 shallower one will first lose more water by evaporation because of 
 the greater rapidity with which the water is heated by the sun, 
 and second because of the larger area from which evaporation is 
 taking place. Counterbalancing this, however, is the fact that the 
 shallow reservoir is usually cheaper to construct, as it involves gen- 
 erally the building of a dam of less height. 
 
 Where the water supply is limited and must be conserved to the 
 highest degree the deep reservoir possesses decided advantages 
 over the shallow one on account of the smaller losses by evaporation. 
 Especially is this true if the storage supply must be carried over from 
 wet to dry years. In order to compare the merits of two reservoirs 
 of about the same capacity, the one deep and the other shallow, it is 
 necessary to determine the value of the extra water saved in the one 
 case and compare it with the extra cost of construction. In doing 
 this, due consideration should be given to future iriigation develop- 
 ment and the probable rise in the value of a water supply. 
 
CHAPTER XII 
 DAM SITES 
 
 General Conditions. — A feasible site for a storage dam is one 
 where topographic conditions are such that the outlet from a 
 large basin or valley may be permanently closed with a relatively 
 small amount of material. The ideal site especially for a high dam 
 is one where solid rock occurs in the bed and sides of a stream and 
 where suitable material for building, preferably good rock, can be 
 obtained in the immediate vicinity. Unfortunately good sites are 
 extremely rare and often the skill of the engineer must be exercised 
 in making use of localities not particularly favorable and in building 
 with such materials as are most accessible. From the ideal condi- 
 tions of a solid-rock foundation and a good quarry from which to 
 obtain suitable rock for a dam, he must usually depart, and seek to 
 make a safe structure upon a less firm foundation and from less 
 suitable materials. Nearly ideal conditions are those shown in 
 Plate XI, Fig. A, the site of the Roosevelt Dam, Arizona,, before work 
 was begun. 
 
 In some localities the depth to solid rock is so great that it is im- 
 practicable, if not impossible, to excavate to it for a foundation. 
 Such a condition may entirely modify the type of dam to be used and 
 even be a controlling feature in determining the height of dam that 
 can be constructed. The fundamental questions concerning a dam 
 site are (a) quantity of material required for a dam of given height; 
 (b) material in foundation; (c) character of material available for 
 construction; (d) conditions for spillway. 
 
 It is also sometimes necessary to consider the general location as 
 to the practicability of delivering and installing the necessary plant 
 and equipment for construction. It is not until the above questions 
 have been answered by careful field examinations that the feasibility 
 of any site can be established. 
 
 Surveys of Dam Site.^ — Having determined by general reconnais- 
 sance that a certain reservoir site is the best available for the storage 
 of a given supply the next step is to select a site for a dam. As a rule 
 there are several possible sites more or less contiguous to each other 
 where a dam might be built, and there must be a balancing of the 
 
 190 
 
DAM SITES 191 
 
 relative advantages and disadvantages of each. One location may 
 require a little less cubical contents for the dam itself, but may 
 require a deeper foundation. Another may be nearer the material 
 suitable for construction, but require a greater cubical content. 
 For each of these sites tentative plans should be made and careful 
 estimates prepared in order to weigh their relative costs_ and 
 merits. 
 
 The first steps in considering a given site is to prepare a careful 
 topographic map of it. This map should be on a scale sufficiently 
 large to permit quantities both for the dam itself and the foundation 
 excavations being determined to a reasonable degree of accuracy. 
 (See Fig. 38.) Ordinarily a scale of from 50 to 100 ft. to the inch 
 and contour intervals of from i to 2 ft. are required. Topographic 
 maps are not only valuable in preparing estimates, but also serve a 
 useful purpose in the laying out of a construction plant and provid- 
 ing for the handling and storage of material. 
 
 The most economic and convenient method of making such survey 
 is by means of a plane-table, as it is usually possible to cover the 
 entire site from a few well-chosen stations and to sketch with great 
 accuracy the topography of all salient points. 
 
 Foundation. — The determining factor after the consideration of 
 the general location of a dam is the character of the foundation. 
 Upon this may depend the height of dam which it is feasible to con- 
 struct and the amount of storage capacity which may be made avail- 
 able. While it is relatively a quick and easy piece of work to make 
 the topographic sketches showing surface features, it is not at all easy 
 to ascertain the underground conditions which limit the character and 
 cost of the structures. In general it may be said that the foundation 
 is the most costly as well as the most vital point of a dam. Practic- 
 ally all failures come either through lack of knowledge of the founda- 
 tion conditions or the neglect to take these conditions into account in 
 planning the structure. The fundamental requirements of a founda- 
 tion are stability or bearing power to carry the weight of the dam and 
 water-tightness to resist percolation under the artificial structure. 
 
 The bearing power of a foundation determines to a great extent 
 the character of structure which may be buUt. It must in every 
 case be sufiScient to carry the load imposed upon it without un- 
 due settlement. For high masonry dams a foundation is required 
 which is practically unyielding for its load, since settlement especially 
 under one part of the dam may produce stresses sufficient to rupture 
 the masonry. For a low dam or one buUt of non-consolidated mate- 
 
192 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 rials which require great thickness and width of base to sustain the 
 water pressure less firm foundations may be used. For example a 
 dam of loose rock and earth may be safely constructed upon a founda- 
 tion of firm earth. In a structure of this kind a slight settlement in 
 the foundation is taken care of by the large mass of non-consolidated 
 material above gradually assuming a lower position. Here also it 
 is necessary however, that unequal settlement of any considerable 
 magnitude be avoided on account of the danger of opening fissures 
 in the dam. 
 
 Water-tightness as applied to foundations is a relative term as all 
 earth and most rocks are more or less porous to water under high 
 pressures. But, hard, compact rock, without fissures may for 
 practicable purposes, be considered as water-tight. In the most 
 compact rock, however, seams or fissures are frequently found. 
 Earth, especially that found in the bed of streams or old waterways, 
 is likely to be made up of strata of varying character, some of which 
 permit the passage of water through them. While the existence of a 
 semi-porous material in a foundation may not be sufficient to pre- 
 vent its use, it is of the highest importance that a knowledge be had of 
 the character and location of such materials in order that suitable 
 plans may be prepared. 
 
 Borings and Test Pits. — ^The most complete examination which it is 
 practicable to make is really none too good in determining the char- 
 acter of foundation. There is little excuse for the engineer attempt- 
 ing to make plans for a dam without first obtaining full information 
 concerning the conditions below the surface of the ground. The cost 
 of such examinations, though large, is not prohibitory, and funds 
 expended in this manner usually result in the greatest ultimate econ- 
 omy. For making such examinations there are commonly employed 
 test pits, wash borings and core borings. 
 
 The simplest and most common method of making examinations in 
 dry earth or indurated material is by means of ordinary test pits or 
 open wells dug by hand. In all parts of the country are to be found 
 laborers who have had experience or who can be quickly instructed 
 in the matter of digging and shoring out the open hole. Such test 
 pits afford access to the ground in a way which permits very thorough 
 examination. 
 
 It frequently happens that the conditions are such that the ordi- 
 nary open test pits cannot be economically utilized over the entire 
 area. This is especially the case if the amount of water encountered 
 is too great to be handled by ordinary pumps. It then becomes 
 
Plate XI 
 
 Fig. a. — Storage dam site, Roosevelt Dam. Salt River Project, Ariz. 
 
 Fig. B. — Drilling for bed rock at storage dam site. Shoshone Project, Wye. 
 
 {Facing Page 192) 
 
Plate XI 
 
 Fig. C. — Spillway of Bumping Lake dam. Yakima Project, Wash. 
 
 Fig. D. — Spillways of Roosevelt Dam. Salt River Project, Ariz. 
 
DAM SITES 193 
 
 necessary to procure some form of apparatus for more systematic 
 work. Recourse is usually made to the ordinary well diiller who, with 
 suitable "rig" or outfit is accustomed to drilling wells through sand, 
 gravel, boulders, and solid rock. He can usually determine with 
 reasonable degree of accuracy the character and thickness of the dif- 
 ferent layers or strata, and if skillful can shut off the surface flood and 
 ascertain whether the deeper strata are fissured and carry consider- 
 able amounts of water. 
 
 Great care must be observed in taking and studying the material 
 brought up. The form of drUl ordinarily employed shatters and 
 pounds the rock into sand or powder and there is constant tendency 
 for material dislodged from the upper part of the hole to fall down 
 and become mixed with that which is being broken at the bottom. 
 The material as it is brought up in a baUer is washed with water 
 in such way that the finer particles are apt to be lost and the samples 
 examined thus represent usually the harder portions of the rocks 
 penetrated. 
 
 Where the foundation material consists of rock or indurated mate- 
 rial, it is desirable to use some form of core bit for cutting rather than 
 the chopping tool referred to above. There are various forms of core 
 bit operated with a rotary motion, sometimes armed with diamonds 
 or borts. These cut away an annular space, leave a central core which 
 can be removed for study. The softer layers tend to disappear and 
 care must be exercised in measuring the depth of the hole to account 
 for any soft layer which may be passed through and so completely 
 ground to powder as to be unrecognizable. If a continuous core 
 can be had, this will furnish a fairly complete record of the rocks 
 penetrated. 
 
 The cost of test pits and drill holes varies with the locality. This 
 in tiurn governs largely the price of labor and material. In general 
 it may be said that for ordinary test pits up to 20 or 30 ft. in depth, 
 the cost per vertical foot is between $1 and $2. For the ordinary 
 chopping bit where holes are put down to a depth of 50 or 100 ft., 
 and aggregate possibly a thousand feet or more, the cost should be 
 approximately the same. For the diamond or other core bit, the 
 cost may be from^ $3 to $5 per vertical foot. A view of a diamond 
 drill equipment mounted on a scow at the Shoshone dam site, 
 Wyoming, is given in Plate XI, Fig. B. 
 
 The cost per foot is dependent largely upon the number of feet 
 drilled in the same locality as one of the principal items of expense is 
 procuring, moving and installing the apparatus. After it is once in 
 
 13 
 
194 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 place and in operation, the number of feet drilled may be increased 
 at wiU and the cost per foot materially reduced. 
 
 The number of test pits or borings which must be made is, of course, 
 dependent upon the material encountered and can rarely be deter- 
 mined in advance, if for example, a half dozen borings are made at 
 fairly regular intervals across the proposed site and all show practic- 
 ally identical results, there is very little apparent need of iacreasing 
 the number. If, however, each test pit or boring shows some different 
 condition and gives rise to suspicion as to the safety of the foundation, 
 then the number must be increased until the experienced engineer 
 feels that he has a fairly complete knowledge of the conditions. 
 
 Character of Foundation. — The character of materials in a founda- 
 tion are as diverse as are the components of the earth's crust. 
 Passing beneath the surface cover of soil, if any, on the hill sides, 
 and of clay, sand, and gravel of the river bottom, there is usually 
 encountered a layer of disintegrated material, resulting from the 
 weathering of the underlying rocks. These may be horizontal 
 or partly inclined or even vertical. They may be shattered, faulty, 
 or may be in thin shaley layers or in massive blocks. All of the 
 essential facts concerning the material, its position, especially its 
 permeability to water under pressure, should be thoroughly under- 
 stood before the final plans are determined upon. The test pits 
 or drill holes should be continued not merely into the firm rock but, 
 depending upon the geologic structure, a few at least should be 
 put down to a depth of loo or more feet, to be certain as to the 
 still lower strata. Especially is this necessary in a region of eruptive 
 or crystalline rocks. For example, there are instances where dams 
 have been built upon lava supposed to be of great thickness, but 
 which ultimately proved to be a relatively thin shell, with clay 
 underneath. In another case, plans were made for a very elaborate 
 structure, when a deep drill-hole revealed the fact that the crystalline 
 rock on which a part of the dam was founded was in reality a clifE 
 overhanging a former pocket in the river bed and beneath this 
 was an ancient river channel fiUed with gravel. 
 
 For high masonry dams where the loading on the foundation 
 is heavy, the crushing strength of the rock should be determined, 
 especially where the softer varieties of rock are encountered. 
 
 Character of Materials for Construction. — Having determined 
 the character of materials composing the foundation, it is required 
 next to ascertain what materials in the vicinity are best suited for 
 building the dam. 
 
DAM SITES 195 
 
 Assuming that the foundation is of solid rock it is highly probable 
 that other rock can be found in the vicinity suitable for some form 
 of construction. If so, quarries should be opened by experienced 
 men at the earliest practicable date to ascertain the character and 
 size of stone which may be had. The actual opening of a quarry 
 has sometimes revealed the existence of conditions which have 
 necessitated an entire change in plans or methods of constructing 
 the work. For example, as the Laguna Dam, on the Colorado 
 River, Arizona-California, the outer shell of granite was firm and 
 could be quarried into large blocks. From this it was assumed that 
 the rock below the surface would be still better. The opening of 
 the quarries, however, revealed the fact that the surface rock was 
 the only fair material available. 
 
 If rock of large size, weighing a ton or more cannot be obtained 
 economically, the next consideration is whether the material is 
 suitable for being crushed and used in concrete. Where foundation 
 conditions are unsuitable for a masonry structure, or where suitable 
 rock for masonry cannot be obtained, consideration must be given 
 to unconsolidated material. This requires a study of the problem 
 of making a substantial and water-tight structure of loose rock, 
 gravel and earth, or in some cases of earth alone. If an uncon- 
 solidated or loose structure is to be built, the vital point, so far as 
 material is concerned, is to find a clay or combination o.f clay and 
 sand or gravel which, when mixed in proper proportions, is practi- 
 cally impervious or water tight. Such a dam in effect consists 
 merely of an impervious layer properly held and sustained in posi- 
 tion, the remaining materials being simply for the purpose of pro- 
 tecting the water-tight portion of the dam. 
 
 In a timber country, especially where dams of a relatively tempo- 
 rary character are required, consideration must frequently be given 
 to the use of wood and stone. The first question as regards material 
 is to find trees of suitable size and quality of timber for supplying 
 logs for building cribwork, and next to this is the obtaining of rock, 
 preferably large stone, for filling the cribs and preventing their 
 being washed away. 
 
 Accessibility of Materials for Construction. — Next in importance 
 to foundation conditions and materials for construction is the 
 accessibility of these materials to the site of the work. It is some- 
 times the case that the best materials for construction purposes are 
 so located or are at such a distance from the dam site as to make 
 the cost of transporting them almost prohibitive. It frequently 
 
196 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 becomes a question of judgment whether it is preferable to go to 
 some distance from the work in order to obtain the most suitable 
 material, or to attempt to make a safe structmre from less favorable 
 materials which are found in the immediate vicinity. In deciding 
 this question consideration should be given first to the item of 
 safety and second to that of cost. 
 
 In determining the cost of delivery of material to the dam, the . 
 conditions under which it must be excavated, length of haul, charac- 
 ter of roads and methods of transportation must be considered, 
 The magnitude of the work is also of prime importance in deciding 
 what means of transportation it is feasible to employ. For example, 
 a plant which would handle a million yards of material at a low 
 unit cost might result in very high unit costs if used for one-half 
 or one-fourth this amount. It consequently becomes a question of 
 determining for each particular job the most economic methods of 
 transportation. 
 
 Before it can be said that material is accessible to a given site 
 at a reasonable cost the methods of transporting the material 
 and the cost of the equipment required must be carefully determined. 
 With a good foundation and with quarries located at a reasonable 
 distance, it may be found advisable to build an earth- and rock- 
 fiU dam rather than attempt to haul stone from the quarry for a 
 masonry structure. 
 
 Spillway. — Even of more immediate importance than the determi- 
 nation of the character of foundations and materials to be used in 
 constructing the dam is the provision for the safety of the structure 
 by having ample spillway capacity for the discharge of excess waters. 
 This should be so planned and built that it cannot be obstructed by 
 any probable accident, nor be closed readily even by deliberate act. 
 It is the safety-valve which insures against loss of life and property 
 and as such should not be a subject of any possible or probable 
 closure. 
 
 The ideal situation for a spillway is at a point not immediately 
 contiguous to the dam where the water can overflow in a broad sheet 
 and be collected into a channel through which it may reach the river 
 at a point sufficiently far below the dam so as not to disturb the 
 foundations. In some situations it is impossible to find such a spot 
 and the spillway must be built on the natural rock or soil as part of 
 the dam itself, and here great precautions must be observed to hold 
 the water in check and to absorb its energy of motion in such way as 
 not to have it injure the structure. 
 
DAM SITES 197 
 
 A criticism which has been applicable to many of the dams built 
 in the past has been that the spillways have not had sufficient 
 capacity for the extraordinary floods. Provision has been made for 
 the average high water, but the failure of some of these structures 
 illustrates the fact that the great flood of the century is one which 
 far exceeds the average high water and may occur immediately after 
 an ordinary flood has filled all the basins and river channels. The 
 fact that the reservoir frequently acts in such way as to absorb most 
 of the flood water and does not permit any to escape tends to give a 
 false sense of security, or the fact may be pointed out that water has 
 never reached nor filled the existing spillway and therefore there is 
 little to be feared that it ever will. This is the fallacy which has 
 resulted directly or indirectly in many catastrophes. Succeeding 
 structures have been built with small spillways because of the fact 
 that dams already erected have not been threatened by the small 
 capacity already provided. In this, the fact is ignored that the 
 record of a few years or even of a decade or more is not to be relied 
 upon for the extraordinary conditions or combinations which may 
 occur and for which the spillway must be arranged. 
 
 The condition to be sought besides those of safe location and ample 
 capacity is solid rock which can be built upon in such way as to form a 
 long sill or weir over which the floods may pass. Usually if rock 
 exists in the right location it is necessary to cut this down to the de- 
 sired elevation. . Occasionally the quarries for supplying material 
 for the dam can be located in the proposed spillway, as at Roosevelt, 
 Arizona, (Plate XI, Fig. D) so as to make use of the material re- 
 moved. If, however, the rock is already too low it may be brought 
 up to a proper elevation by a low masonry dam forming thus a sub- 
 sidary structure to the main work. 
 
 In some localities, for example, in a narrow canyon as at the 
 Shoshone Dam in Wyoming, it has been necessary to cut a tunnel 
 through which the floods may discharge. In this case, the over- 
 flow sill is constructed on a curve at the head of the tunnel, thus 
 forming a brpad funnel approach in which the water may be 
 gathered. 
 
 Occasionally a spillway must be over earth or gravel or partly 
 indurated materials which are easily worn away by water. In such 
 cases ample protection must be provided by structures preferably 
 of concrete or masonry and the water which passes over the spillway 
 must be collected in a channel protected from backcutting by being 
 lined with concrete or timber (Plate XI, Fig. C). Provisions must 
 
198 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 also be made by means of chutes or drops by which the water will 
 expend its energy internally or against some indestructible material. 
 Timber has occasionally been used in connection with spillways, but 
 the disadvantage is that, as these spUlways receive water perhaps at 
 intervals of many months or once a year or longer, the wood is dried 
 out, warps, or decays, so that when brought into use suddenly the 
 structure may faU. For this reason, as above stated, concrete or 
 masonry is most generally employed. 
 
 Records of Stream Flow. — In considering the size of spiUway, it is 
 necessary to have records of stream flow not only giving the total 
 amount but even more important, the details of behavior of individ- 
 ual floods. It may be assumed that as far as the spillway is concerned 
 the flow through the greater part of the year is insignificant, as it is 
 stored in the reservoir, but the critical points are on the probable 
 behavior of the stream at extreme high water. It is particularly 
 important to know the intensity of the flood or the amount of water 
 delivered at short intervals during the height of the flood. Assump- 
 tions must be made, based upon a full reservoir, with a flood coming 
 from the entire drainage basin. If this basin is heavily wooded or 
 covered with a thick growth of bushes and grass, the rate at which the 
 flood will reach the reservoir and consequently must be discharged 
 over the spillway may be assumed as relatively small. If, on the 
 contrary, the drainage basin consists largely of rock and uncovered 
 soil, or is traversed by roads and paths, which in time of storm act as 
 collecting drains, then the rate at which the water will reach the 
 reservoir is greatly increased and hence the probability of need of 
 providing a large overflow. 
 
 Consulting the rainfall records, it is seen that a rate of i in. 
 per hour for the entire basin is extremely heavy, although as high 
 as 3 in. per hour have been known in tropical countries. If the 
 drainage basin consists of 12,000 acres, this would mean 1,000 acre- 
 feet occurring in an hour or at the rate of 500 second-feet continued 
 through twenty-four hours. 
 
 In other words, assuming that all of the water on this drainage 
 basin will reach the reservoir within a day a spillway of at least 500 
 second-feet must be provided. As a matter of fact, however, 
 much of this water might reach the reservoir in a shorter time and 
 the spillway must be correspondingly increased. 
 
 A large factor of safety must always be employed so that after 
 estimating the largest probable flood, it is the part of wisdom to 
 multiply this by two at least, sometimes by a larger factor, if the 
 
DAM SITES 199 
 
 records of rainfall or river flow have not been extended over several 
 decades. 
 
 Kind of Dam Best Adapted to Suit Conditions. — From what 
 has been stated above, it is evident that the kind of dam must be 
 determined by the conditions already discussed of foundation 
 and materials available. Plans may also be modified in accordance 
 with the funds which are at hand and the prospective returns from 
 the investment. If the foundations are good, that is, of solid rock 
 and quarries of suitable rock are available, a masonry structure 
 may in general be considered as the best, but something cheaper 
 may be allowable if the financial ability of the builders will not 
 permit the better structure. The great danger in this connection 
 lies in attempting to reduce the cost below reasonable limits of 
 safety. 
 
 Having determined upon the most economic type of dam and 
 then having modified this to suit financial requirements and brought 
 it to a minimum of safety under the direction of an experienced 
 and competent engineer there is sometimes a tendency to practise 
 a false economy in the character of work and quality of materials 
 used in construction. In some cases the work is entrusted to a 
 builder, who in his desire to lessen the cost reduces the dimensions 
 of the dam and still further cuts down the factor of safety. This 
 has been the cause of several failures; the plans were modified by 
 experienced men to a point where they could no longer permit 
 further reductions of cost and then the work was entrusted to men 
 who still further cut down the requirements, not letting it be known, 
 however, that the approved plans were being changed in detail. 
 These changes were not discovered until after some catastrophe 
 had occurred and the question was raised as to whether the dam 
 had been correctly designed or a proper type of structure adopted. 
 
CHAPTER XIII 
 TIMBER DAMS 
 
 Kinds of Dams. — ^A dam is an obstruction placed across a stream 
 or depression and so devised as to hold back or obstruct the flow of 
 the water. It may be buUt in such way that water will flow over 
 it, in which case it is termed an overflow or submerged dam or weir; 
 or it may be of such height that it cannot be overtopped. In the 
 latter case, if relatively long and low, it may be termed a dike or 
 levee. 
 
 The essential feature of any dam is the relatively impervious 
 layer, curtain or blanket held in place by a suitable arrangement 
 of material. The whole structure may be impervious or only a 
 thin section of it either in the interior or against the upper or water 
 face. The material which holds this impervious layer in place may 
 be of wood such as logs or of earth properly compacted, of stone either 
 loose, or carefully laid, of concrete, brick, steel, or almost any other 
 building material. 
 
 This material may be arranged simply as a great mass dumped 
 in together or may be carefully proportioned and built to secure 
 the greatest economy of material, following the rules laid down 
 by scientific observation of the strength of materials and deductions 
 based upon mathematical principles. 
 
 Dams are classified according to the material of construction and 
 its arrangement in the structure. One form grades by insensible 
 degrees into another, but the following may be distinguished: 
 
 Timber dams, including brush dams and log or crib dams. 
 
 Earth dams. 
 
 Rock-fill dam's. 
 
 Rock and earth-fill dams. 
 
 Masonry dams. 
 
 Early Stages of Development. — The most elementary form of dam, 
 so far as known, is that constructed by the beavers or their relatives. 
 Examples of the work of these animals are to be found in various 
 sections of the country and the rude skill displayed by them in using 
 timber and earth and stone to form an obstruction for holding up 
 
 200 
 
TIMBER DAMS 201 
 
 small heads of water causes us to question whether it is not from them 
 that man learned his first lesson in this branch of engineering. 
 
 The early dams built by men were constructed of small logs and 
 brush, and, like the beaver dams, were arranged in such a way as to 
 have the branches interlaced so as to form a more or less systematically 
 interwoven mat or rude fence. Man learned to improve upon these 
 methods by holding the light material in place, and prevent its being 
 floated away by means of loose rock. Larger logs were also soon 
 used, these being arranged more and more regularly until by degrees 
 there was an evolution from the irregular brush and stone dam to the 
 systematical dam in which the logs are arranged in geometrical forms 
 with the spaces between filled with carefully placed rocks, both large 
 and small. 
 
 In the earlier stages of irrigation the brush and stone dam was 
 largely used for diverting water from the stream into the canal as 
 shown in Plate XII, Fig. A. For the small irrigation systems where 
 each canal supplied water to but a few farms, it was by far the most 
 economic structure that could be used. At high water it was usually 
 wholly or in part washed away, but this did not result in any notice- 
 able loss. After the stream subsided in summer so that the water 
 no longer flowed freely into the head of the canal, the farmers 
 assembled, cut the necessary brushes from the adjacent banks of the 
 stream, floated these into position and secured the mat thus made by 
 placing boulders and small stone upon it. In plan, the dam was 
 usually placed diagonally up-stream from the intake of the canal 
 so as to force the current directly toward it. 
 
 Improvements on this rude form were later made by tying the brush 
 together with wire and anchoring it to posts. As the water still 
 further subsided, the dam was made more nearly water tight by 
 throwing gravel, sand and earth against its upper side. The total 
 outlay of time and labor required for this work was not usually great 
 and the annual cost of replacement less than the interest and depreci- 
 ation on a more permanent structure. 
 
 After crop production and land value increased a point was reached 
 when it was not economy to repair these dams annually, or after each 
 flood, and consideration was given to a more permanent form of 
 structure, one which did not necessitate men leaving their farms at 
 the critical time of crop seasons for the purpose of making repairs. 
 It also frequently happened that the inlet of the canal was at such a 
 height above the bed of the stream that the brush dam was not 
 sufladent to force the low water flow up to it. In that case, a struc- 
 
202 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 ture was required which would raise the water and which would be 
 strong enough to resist the floods. The next step was therefore the 
 consideration of a dam built of more substantial materials. It is thus 
 seen that the timber dam is, to a certain extent, the outgrowth of 
 more systematic arrangement of the same class of material used in 
 the brush and stone dam. One of the intermediate types of dam is 
 shown in Plate XII, Fig. B. 
 
 Use of Timber Dams. — In regions where timber is plentiful and 
 consequently cheap, timber or timber and stone dams are extensively 
 used. As a rule this use is confined to diversion wiers or submerged 
 obstructions the water flowing over .them at aU times when there is a 
 sufficient supply in the stream. In some cases timber dams are also 
 used for storage reservoirs where comparatively low heads are 
 required. 
 
 Where wood is exposed to both wet and dry conditions, its tendency 
 to decay is rapid. For this reason timber dams used in streams 
 •which are dry during a portion of the year, or where there is a wide 
 variation of head against them must be considered as temporary in 
 character. The conditions which will justify the construction of a 
 temporary structure of this kind will vary in each particular case and 
 locality. 
 
 Where Timber Dams are Applicable. — ^Timber dams are applicable 
 for practically all conditions where a low head (20 ft. or less) is re- 
 quired and where there are suitable materials available at reasonable 
 cost for their construction. The principal materials required are logs, 
 either rough or sawed into square timbers or planks, and stone vary- 
 ing in size up to 200 lb., or even more. They are especially adapted 
 to regions where trees of suitable size and quality for logs can be cut 
 on the upper reaches of the stream and floated into position. 
 
 Timber dams may be adapted to practically any kind of founda- 
 tion conditions, from solid rock to comparatively soft earth, by 
 giving them sufficient width of base and using cut-off walls where 
 required to avoid percolation under the dam. Except on solid-rock 
 foundation, it is necessary also to protect the lower toe from erosion 
 and undermining the structure. If properly constructed their safety 
 is not endangered by slight settlements, and for this reason the tim- 
 ber dam may be constructed on a foundation which would be unsuit- 
 able for a less elastic structure, such, for example, as .masonry. (See 
 Plate XII, Figs. A and B.) 
 
 The plan of the dam may be straight or curved, and built at 
 right angles to the current or diagonally with it. The latter plan 
 
Plate XII 
 
 Fig. a. — Brush and stone dam, typical of pioneer conditions. Las Cruces canal, 
 Rio Grande, N. Mex. 
 
 Fig. B. — ^Log and earth dam. Cimarron River, N. Mex. 
 
 (^Facing Page 202) 
 
Plate XII 
 
 Fig. C. — Foundations for timber dam. Yakima Project, Wash. 
 
 Fig. D. — Apron of partly finislied timber dam. Yakima Project, Wash. 
 
TIMBER DAMS 203 
 
 is sometimes used in order to increase the length of overflow and 
 decrease the depth of water on the crest. In this case there is a 
 tendency, however, to force the stream toward one bank, with 
 consequent danger of erosion, or if directed toward the intake of 
 the canal, with liability of throwing the floods into the head and 
 bringing in large quantities of sand, gravel and debris. 
 
 A curved plan of timber dam has occasionally been used in order 
 to gain the advantage of the effect of the arch. The water pressure 
 against the up-stream face putting the structure in compression. 
 The gain in this respect is not very great, but is worthy of con- 
 sideration if the abutments are sufficiently firm. 
 
 Conditions of Stability. — Unlike a masonry, concrete or similar 
 rigid structure, a timber dam is not dependent for stability on each 
 part being held by friction or by the resistance due to cohesion of the 
 various parts. On the contrary, it is essentially a wooden frame 
 tied together in such a way as to be moderately elastic and held 
 from floating or sliding by its loading of rock, which in turn is held 
 in place by the network of timbers. This sort of structure allows a 
 certain amount of settlement or sliding and an adjustment under 
 pressure of gravity so that a change in position which might be 
 fatal to almost any other form of dam may tend to strengthen 
 rather than weaken the structure. 
 
 Timber dams are sometimes also built with such an up-stream 
 slope that the weight or downward pressure of the water tends to 
 hold them firmly on the foundation so that the added weight of 
 water with increased head tends to strengthen the factor of safety 
 against sliding. 
 
 The principal features to be safeguarded in the construction of 
 timber dams are: 
 
 (a) Protection against sliding on the foundation. 
 
 (b) Bonding together of the various timber elements. 
 
 (c) Protection against undermining. 
 
 Sliding on the foundation, as heretofore mentioned, is provided 
 against by weighting the structure by means of heavy rock, and in 
 some cases also by constructing the up-stream slope at such an angle 
 that the weight of the water exerts a vertical component through 
 the dam on its foundation. The holding of the dam together may 
 be accomplished by means of drift bolts driven through the various 
 timbers so as to securely tie them together at each point of junction. 
 
 The dam may be protected against undermining, if it be on other 
 than solid-rock foundation, by carrying an apron for some distance 
 
204 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 down-stream below the lower tow. It is necessary also to give 
 protection against cutting around the abutments by constructing 
 the dam well into the banks or providing masonry abutments 
 against which it may rest. 
 
 Additional strength is sometimes given to timber dams by con- 
 structing them either in the form of an arch or "V" shape. Dams 
 built in this form must have solid banks against which the ends may 
 rest, or masonry bulkheads should be constructed. If artificial 
 abutments are used, they should be carried up above the flood 
 line of the stream. 
 
 Water-tightness. — Timber dams are made water-tight, or nearly 
 so, by means of a tight facing of either earth and gravel or of wood. 
 This water-tight facing should be located at the up-stream face of 
 the dam. In general, it is believed that a water-tight facing of earth 
 and gravel is superior to that of lumber on account of its greater 
 lasting qualities, and also its tendency to remain tight under low- 
 water conditions. 
 
 The interior spaces of the dam should be filled with loose rock and 
 where available, gravel should be carefully packed around the various 
 timber members in order to further protect them from decay. The 
 interior of the dam should be sufficiently porous that water which 
 may find its way through the water-tight face will be quickly 
 drained away. 
 
 Types of Timber Dams. — ^Various types of timber dams have 
 been successfully used and it is impossible to say that any one type 
 is superior to another. Each particular design should be made to 
 suit local conditions of foundation and material available for con- 
 struction, for example, in a locality remote from mills, a design 
 adapted to the use of round logs would be probably more economical 
 than one of sawed timbers, even though the amount of material 
 required in the former case was greater than in the latter. On the 
 other hand, in a locality where timber is less plentiful and where 
 dimension lumber can readily be gotten, a saving might be effected 
 by using sawed timbers and so designing the structitte as to require 
 the minimum amount. 
 
 Practically all of the different types of timber dams depend upon 
 the principles heretofore given for stability and water-tightness. 
 
 Among the more common types of timber dam which may be 
 mentioned are log and brush dams, crib dams, combination crib 
 and pile dams, and framed dams. 
 
 Log and Brush Dams. — ^This type of dam is well suited to local- 
 
TIMBER DAMS 205 
 
 ities where timber, preferably long trees, can be obtained without 
 diflSculty. It consists essentially of a series of mats of logs of various 
 lengths laid in the stream parallel with the current. The tops of the 
 trees in each case being placed up-stream. At the lower face of the 
 dam the various layers of mats are separated by means of one or 
 more rows of fairly uniform sized logs carried crosswise. This has 
 the effect of building up the lower portion of the dam more rapidly 
 than that portion further up-stream, and giving a long flat slope to 
 the upper face as shown on Plate XII, Fig. B. The horizontal and 
 longitudinal timbers which form the lower face of the dam should be 
 securely fastened together by means of drift bolts, or otherwise. 
 
 In a dam of this kind a thin layer of gravel and fine brush should 
 be placed between the various courses of the timbers and the struc- 
 ture should be given weight and stability, as well as water-tightness 
 by covering the up-stream face with earth, loose rock and gravel. 
 
 It is well to allow the first two or three courses of timbers to 
 project some distance down-stream below the toe of the main dam, 
 thus forming an apron for protection against erosion. For a dam 
 of moderate height, say from 8 to lo ft., the first, or bottom layer of 
 timbers should project down-stream from 20 to 30 ft., the second 
 layer from 10 to 15 ft. and the third layer from 5 to 8 ft. 
 
 Crib Dams. — This forni of dam consists essentially of a series of 
 timber cribs built up across the stream and fiUed with loose rock to 
 prevent their being washed away. These cribs are commonly built 
 of either round or sawn timbers. They may also be built of various 
 shapes and sizes, depending upon the material available and the 
 height of dam required. (See Plate XII, Figs. C and D.) 
 
 A common form of crib dam consists of a series of rectangular 
 cribs from 10 to 15 ft. square carried in a straight line across the 
 stream. Where the foundation is of solid rock it is a common practice 
 to excavate into the rock sufficient to receive the first row or timbers. 
 The first or second layer of timbers from the foundation are usually 
 laid close together so as to form a floor in each of the cribs for 
 holding the rock. The timbers are all securely fastened to each 
 other at their junctions by means of drift bolts or pins. Water- 
 tightness is secured by means of a facing of gravel and earth, or some- 
 times of planking. 
 
 An apron for protecting the lower toe of the dam in case of floods 
 is frequently made by constructing a second row of low cribs below 
 the main dam and filling them with rock. 
 
 In other forms of dams the cribs, instead of being built up verti- 
 
206 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 o 
 
 > 
 
 ■a 
 
 a 
 
 S 
 
 
TIMBER DAMS 
 
 207 
 
 cally, are inclined on the up-stream or 
 thus giving a triangular section. 
 A crib with the inclined face up- 
 stream has the advantage of util- 
 izing the downward pressure of 
 the water in producing a greater 
 degree of stability. Also, one 
 with an inclined down-stream 
 face tends to carry the overflow 
 in time of floods away in a more 
 nearly horizontal direction and 
 with less liability of erosion at 
 t'he toe than is the case when the 
 fall is vertical. 
 
 Crib and Pile Dams. — A com- 
 mon form of dam and one 
 adapted to a soft bottom, which 
 does not contain quicksand, is 
 the combination of driving pUes 
 and against these building the 
 crib work. 
 
 Two or more rows of piles are 
 driven directly across the river at 
 right angles to the current. The 
 cribs are then constructed between 
 the rows of piling and filled with 
 rock or rock and brush. As an 
 illustration of this tjrpe of dam, 
 is that on Yellowstone River, 
 Montana, below Glendive, a part 
 plan of which is given in Fig. 39, 
 together with location, plan and 
 cross-section of the river. 
 
 In Fig. 40 is given the cross-sec- 
 tion of the dam showing the rela- 
 tive position of the piles and the 
 braces, with apron and protecting 
 rock below. 
 
 A modification of this form 
 is to drive a double row of 
 piles across the stream with a 
 
 down-stream face or both. 
 
 B Ma's \\\ 
 
 " -si si I B- «te 
 
 iW* S|\ »-a"S "t, 
 
 
208 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 clear space of about 2 ft. between them. The piles in each row 
 are placed immediately above and below each other and spaced 
 the same distance apart as the two rows are distant from each 
 other. These spaces between the piles are then filled with logs 
 built up crib fashion and laid at right angles to each other. The 
 logs parallel to the direction of the current are allowed to project 
 some distance up-stream so as to form the upper face of the dam, and 
 terminating on the lower side just below the lower row of piling. 
 Care must be taken in driving the piles so as not to permit the river to 
 scour out the bottom between them, and thus permit a current to get 
 started under the crib work. Protection of the bottom during the 
 driving of the piles and construction of the dam may in some cases be 
 secured by means of brush mattresses. Where this cannot be done it 
 is sometimes advisable to first float the cribs into position and then 
 drive the piles through the cribs, the latter serving to protect the 
 bottom from erosion. 
 
 Framed Dams. — The frame tjrpe of dam requires far less timber 
 than the ordinary log or crib dams heretofore described. For this 
 reason it is better adapted to localities where timber is scarce. For 
 convenience in framing the timber should be sawed to regular 
 dimensions. 
 
 The dam consists essentially of framed timber bents placed 
 parallel with the current. The bottom timbers of the bents are 
 fastened to cross sills set into the foundation and securely anchored. 
 Where the foundation is on rock the anchorage may be made by 
 means of iron bolts split at the lower end and wedged into holes 
 drilled in the rock. 
 
 The upper face of the dam should be inclined at an angle sufiicient 
 that the vertical component of the water load will act as a weight to 
 prevent sliding. 
 
 Water- tightness is ordinarily seciured by means of a plank face 
 on the upper slope of the dam. The interior spaces between the 
 bents are in general filled with loose rock to give the structure greater 
 stability, although this is not absolutely necessary, safety being 
 insured by the strength of the bents and the water load on the flat 
 upper face. 
 
 The lower toe should be protected by means of an apron carried 
 well down-stream. The lower end of this apron should be further 
 protected by means of piling or rock. The force of the water may 
 also be broken by constructing the lower face of the dam in steps 
 or on an incline. 
 
TIMBER DAMS 
 
 209 
 
 A layer of loose rock or earth and gravel should be placed on the 
 upper face of the dam for some distance above the toe or in place 
 of this a mass' of concrete making a more permanent structure as 
 shown in Fig. 41. 
 
 Upper Approacli 
 Excavated to Eler.2302 
 
 u 
 
 2-8 Boat Spikes 
 to each Log 
 Elev.22S9 
 
 Section of Dam 
 
 6 Hewn Timbers 16'Lonc, Laid Close 
 aud Secured to Logs with 2-H"i 12" 
 Boat Spikes at each Intersection 
 
 -J3 " 
 
 JOS a 
 do*:? 
 
 m3> 
 
 Bottom of Concrete 
 Bottom of Stone Filling . 
 
 All Logs 12'tn Dia.at the Butt. 
 , , Log Drift Bolts I'Bd. 20'long, 
 
 l^Ba"* filled with Plan of Dam 
 
 , Selected Material / // 
 
 \ 6 Hewn Timbers 
 ^'o'-^-SC »'Long. Laid 2" 
 ~^,p, — ^1 r" apart, and Secured 
 
 South Abutment 
 
 Fig. 41. — Concrete, rock and timber diversion dam, Yakima Project, 
 
 Washington. 
 
 Limits of Height. — ^The height to which timbei dams may be built 
 is limited largely by the character of the foundation and quality of 
 material available. There are examples of timber dams with 
 
 14 
 
210 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 heights of from 30 to 40 ft., or even greater, which have stood for 
 years. On a firm rock bed not easily eroded and with heavy long 
 logs and large stone there is no reason why even these heights 
 should not be exceeded. 
 
 Ordinarily the use of timber dams is limited to low heads, gener- 
 ally not exceeding 15 or 20 ft. For such heads cribs may be built 
 of logs or planks floated into position if -the water is sufficiently deep, 
 loaded with rocks and the work carried on with a reasonable degree 
 of safety. For higher structures a greater degree of protection in 
 their building is necessary. 
 
 On account of the temporary character and the possibility of 
 failure after a few years of service, timber dams cannot be strongly 
 recommended for high heads or for localities where any large quantity 
 of water is to be held in storage. For diversion weirs and low dams, 
 especially in localities where timber is cheap they frequently are the 
 most economic form of dam that can be adopted. 
 
CHAPTER XIV 
 EARTH DAMS 
 
 Site for Earth Dam. — The site usually chosen for an earth dam 
 is of such a character that the building of a masonry structure upon 
 it is impracticable. Frequently solid rock foundation conditions 
 do not exist, or even where such conditions do exist suitable materials 
 for the building of a masonry dam may not be available in the 
 immediate vicinity. A firm rock foundation is as desirable for ar 
 earth dam as it is for any other type. It is, however, possible to 
 build an earth dam upon unconsolidated materials such as are 
 usually found in river valleys and consisting of clays, sands and 
 gravels with occasional boulders. It is also possible to use for the 
 body of an earth dam materials that are commonly found convenient 
 to any site which may be selected. 
 
 On account of the conditions above stated possible sites for earth 
 dams are far more common than those suitable for masonry struc- 
 tures. It is not to be assumed, however, that all possible sites are 
 equally satisfactory, or that any which can be found in a particular 
 locality are ideal. The choice of a site is frequently a matter of 
 compromise between alternatives any one of which may be made to 
 serve the purpose but none of which are particularly attractive. 
 It is usually possible to find points of criticism for every site as well 
 as for the type of structure best suited to it. The choice is there- 
 fore not between locations offering superior advantages but rather 
 between those possessing disadvantages which should be avoided. 
 
 Foundation. — One of the principal requirements for the foundation 
 of an earth dam is that it shall be practically water tight below the 
 lower point of the structure. It is essential also that the material 
 be firm enough to sustain the load which is imposed upon it. The 
 latter condition is less likely to give trouble than the former, and 
 there is probably no one question of more importance in connection 
 with earth dams than that of the water- tightness of the material 
 upon which they are built. 
 
 As a rule the surface and sub-surface materials have been laid 
 down by running water which results in their being stratified or 
 consisting of alternate layers of clay, sand or gravel of various 
 
 211 
 
212 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 degrees of coarseness. These layers of pervious materials may 
 consist of small horizontal courses entirely sealed within a thick 
 impervious clay stratum. Or they may extend for several hundred 
 or even a thousand feet and terminate in some open channel or near 
 the surface of the ground below. Water entering one of these sheets 
 or layers of gravel may percolate slowly through it and escape at 
 lower or more pervious points. Where such conditions exist it is 
 essential that they be known and that provisions be made to prevent 
 water in any quantity percolating under the dam. 
 
 Occasionally, the foundation consists of rock disintegrated in 
 place and which has not been rearranged by flowing waters. In 
 this case, there is no definite sorting of the sub-surface material, 
 but this is often loose or porous, because of the solution and removal 
 of the more soluble particles of rock, thus water may pass freely 
 through it or along the old bedding planes. Under other conditions 
 the foundations may be partly filled with material which has rolled 
 in from the sides, such as boulders and smaller debris, the latter 
 partly rearranged by the occasional floods but still quite pervious to 
 water. Too great care cannot be urged in determining the character 
 of the foundation materials especially under high dams. Where 
 these are porous or otherwise unsatisfactory precautionary measures 
 sufficient to insure the safety of the structure must be taken. 
 
 Selection Of Materials. — The materials to be used in an earth 
 dam are governed largely by the character of those found in its 
 immediate vicinity. It is usually not practicable to bring the earth 
 for large structures from long distances excepting possibly a small 
 amount of clay or other impervious substance. The selection 
 of materials for a dam is therefore usually confined to a choice 
 from one or two localities frequently where the formation is not ideal. 
 The location of suitable earth for forming a water-tight embank- 
 ment may govern to some extent the selection of the site for a dam. 
 
 The first and prime requisite for the filling for an earth dam is 
 water-tightness and next to this stability. Finely divided substances 
 such as silts and clays are the most nearly water tight, but frequently 
 do not possess the necessary qualities for being compacted into a 
 firm embankment. Gravel containing a small amount of fine 
 material is capable of being so compacted but does not possess the 
 requisite quaUty of water-tightness. The ideal combination is one 
 composed of gravel, sand and finely divided earth such as silt 
 or clay in such proportions as to make a stable yet impermeable 
 mixture. To meet this requirement the spaces between the larger 
 
EARTH DAMS 213 
 
 particles must be filled and the volume of voids reduced to a mini- 
 mum, and yet with the component particles of such size that they 
 will not slide freely upon each other. 
 
 Occasionally, though rarely, this combination is found in nature, 
 but more often it is necessary to combine materials taken from 
 different localities. In order to do this it is necessary to make a 
 mechanical analysis of those available and combine them in the 
 proper proportions to obtain the desired results. Where such 
 mechanical mixtures are necessary constant vigilance must be 
 exercised during the progress of the work in order to have at all 
 times the proper combination. This is especially true for the im- 
 pervious or up-stream portion of the dam. 
 
 Section of Dam. — The top width and external slopes, or cross- 
 section of an earth dam is governed by somewhat arbitrary rules 
 based upon experience in structures which have stood the test of 
 time. On acount of the varying conditions of saturation and friction 
 in different materials, there is no known law by which the resistance 
 of an earth dam can be computed. As a rule, the slope on the up- 
 stream or water face is made less steep than that on the down- 
 stream or dry side, because of the fact that the saturation leads to a 
 tendency to slide or slough, especially when the water is being drawn 
 down in the reservoir. 
 
 For the upper or wetted slope the minimum is about three hori- 
 zontal to one vertical, although there are cases where a less slope has 
 been chcsen when this could be drained and protected by a suitable 
 covering or by a paving of heavy rock. Dams have been constructed 
 with an up-stream slope of 5 to i although 3 1/2 or 4 to i is as flat as 
 are commonly used. 
 
 For the lower face, the minimum slope is usually 2 or 2 1/2 to i. 
 Occasionally, this is broken by horizontal berms or benches which 
 serve to break the smooth face, give greater thickness tc the base, 
 provide convenient location for surface drains, and for roadways 
 affording access to various parts of the structures. 
 
 The top width is rarely made less than 10 ft. for low structures 
 say up to 30 ft. in height and for dams over this height is ranges from 
 10 to 30 ft., 20 ft. being the width commonly used. 
 
 Prevention of Seepage under Dam. — The points where the arti- 
 ficial structure joins or is placed upon the original earth or rock are 
 those to which most care should be given as along this line of contact 
 water under pressure usually finds most ready access and passage. 
 Great percautions must therefore be taken in preparing the founda- 
 
214 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 tions and in arranging a junction such as to prevent or reduce the 
 amount of seepage along this plane. Such seepage is checked or 
 prevented usually by providing a cut-off trench or wall, extending 
 deep into the foundations, this being extended or sometimes replaced 
 by one or more rows of sheet piling driven as deep as practicable. 
 
 The ground to be occupied by the dam should be carefully cleaned 
 of all stumps, roots or other organic matter liable to decay and all 
 of the loose soil removed down to a depth of a foot or more beneath 
 the surface, this depth being dependent upon the character of the 
 ground. If the sub-soil is firm and free from roots or holes of 
 burrowing animals, the depth of the stripping may be reduced but 
 in general it is better to be on the safe side, and uncover the entire 
 proposed base of the dam to a depth below where the soil shows the 
 effects of penetration by roots and of weathering. 
 
 The material stripped off, if containing a loam, should be placed 
 at one side out of the way for use later on the outer slope of the dam. 
 Any day, sand or other materials of good quality should be similarly 
 disposed of to be utilized later by being incorporated in the body of 
 the structure. 
 
 Placing of Materials in the Dam. — There are in use many different 
 methods of placing materials in the dam, namely, by teams and 
 scrapers, by wagons hauled by horses or traction engines, by railroad 
 cars, by cableways, by mechanical conveyors or by the action of 
 water itself in the hydraulic processes. Selection of the particular 
 method to be used is dependent upon the size of the structure, the 
 location of the materials to be moved, and other conditions. For a 
 small dam it may be impracticable to provide an expensive system 
 of traction, while for a large structure an elaborate preliminary 
 equipment may result in the greatest final economy. 
 
 The simplest method of loosening and moving dirt and one 
 which is generally used in the construction of small earth dams is 
 by plow and drag, slip or wheel scraper. Suitable material found 
 in the vicinity, is loosened by blasting if necessary, plowed up and 
 then havded into place by the scrapers. Skill and care are necessary 
 in depositing the material in such way that it wDl be thoroughly 
 trampled by the horses. It should be kept sufficiently moist to 
 compact readily, and if not well trampled by the men and horses, 
 the earth should be further compacted by systematic rolling. 
 
 In depositing the earth or other material, it should be spread out 
 in thin layers and not allowed to accumulate in small piles. These 
 layers should average not more than 6 to 8 in. in thickness and be 
 
PLATE XIII 
 
 Fig. A.^Foundations for earth dam, showing excavation for puddled core and 
 earth being brought to the site by railroad train, then distributed and rolled in 
 thin layers. Umatilla Project, Ore. 
 
 Fig. B. — Earth dam partly protected by heavy gravel on water side. Boise 
 
 Project, Idaho. 
 
 (Facing Page 214) 
 
Plate XIII 
 
 Fig. C- — Hydraulic construction of earth dam, giant in foreground washing 
 earth and small rocks into flumes supported on trestles and conveying materials 
 to site of dam. Okanogan Project, Wash. 
 
 Fig. D. — Completed dam built by hydraulic process, shown above. 
 
EARTH DAMS 215 
 
 kept wetted by hose or other means to a degree sufficient to give the 
 most dense mass possible when compacted. 
 
 Where large quantities of material are to be handled and especially 
 where the borrow pits are located at some considerable distance 
 such as half a mile or more, it is necessary to provide more economi- 
 cal and quicker modes of conveyance than by horses and scrapers 
 or carts. In such cases, small construction railroads are generally 
 used and trains of from five to ten cars, each holding from 2 to 3 
 yd. of earth or more, are employed. (See Plate XIII, Fig. A.) The 
 earth is usually excavated by steam shovel or similar device, and the 
 cars carry it upon the embankment or upon a trestle adjacent to it. 
 The economy of this method of conveying earth is dependent largely 
 upon the arrangement of the tracks, so that the steam shovel and 
 trains will move in unison and there will always be ready a train to 
 receive the earth from the shovel and at the same time this train will 
 not be delayed in getting its load. In place of the train it is occasion- 
 ally economical to use dump wagons drawn by horses, these being 
 organized in a way similar to that in the handling of trains, the 
 wagons following a certain route, so as to come under the shovel at 
 proper intervals without delay. 
 
 The earth dumped from the side of the trains or wagons must be 
 spread and rolled by some suitable means. This spreading and 
 compacting is usually accomplished by drag scrapers and by horse 
 or steam roller, or similar device. In arranging the trestles for 
 delivering the earth by train at the site of the dam, they should be 
 so planned as not to come within the structure itself. In a few 
 instances, large earth dams have been built by simply side dumping 
 from parallel trestles, as is occasionally done in building large railroad 
 fills. This leaves the timbers embedded in the body of the embank- 
 ment which is allowable in a railroad fill or to a small extent in an 
 earth dam yet the decaying wood may become a source of danger. 
 The embedded timbers if large in aggregate bulk prevent the earth 
 from settling uniformly and there are apt to be spaces along the 
 timbers where the water can find its way and as these rot away the 
 settling becomes unequal and there is liability of leakage or failure 
 of the dam. 
 
 Placing of Materials by Hydraulic Method. — The building of a 
 dam of earth and small rock by hydraulic methods consists essentially 
 of the process of dislodging the material by means of a stream of 
 water undercutting and washing it down, collecting the mud-laden 
 stream in suitable flumes and keeping this stream moving at rela- 
 
216 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 tively high velocity so that it will not deposit the material which it 
 is carrying until the point is reached where it is desired to leave it. 
 
 In order that this process of moving and depositing earth may be 
 economically carried on, it is necessary to have, first, a small con- 
 tinuous flow of water under suf&cient head, say loo ft. or more, so 
 as to have under control a powerful stream which can be directed 
 against the unconsolidated materials, such as clay, sand and gravel, 
 to be moved; second, these materials for economical construction 
 should be at an elevation sufficiently above the location of the 
 proposed dam so that the muddy water will flow by gravity to the 
 point where the materials are to be deposited although they may be 
 lifted by centrifugal pumps; third, the earth or small rock in the bank 
 or pits to be used must be composed of large and small particles, 
 such that when placed these may be mingled to form an impervious 
 mass or core within the body of the dam. If these and other less 
 essential conditions are easily fulfilled it may be practicable to move 
 the material into place at a cost far less than by other means. 
 
 This process of hydraulic sluicing is an outgrowth of the experience 
 of the hydraulic miners of California in washing gold-bearing gravels 
 from ancient river beds. The water for washing is collected in small 
 mountain reservoirs or conducted from a perennial mountain stream 
 by flumes or small canals to a point as near as. possible above the 
 bank to be washed. Here it is turned into a pipe or penstock which 
 terminates in a flexible hose with nozzles designed to give a high 
 velocity to the stream. The arrangement of the nozzles and acces- 
 sory parts for controlling it is known as a hydraulic giant. The 
 giant is so mounted that it can be handled by one or two men, the 
 stream being allowed to play against the bank and moved up and 
 down or swung from side to side in accordance with the judgment of 
 the operator. 
 
 The water striking the bank tears out the lighter portions and 
 undermines the more solid parts. It carries in suspension the 
 smaller particles and rolls along stones up to a weight of loo lb., or 
 even more. As soon as possible after leaving the foot of the bank 
 the stream is conducted into wooden flumes, the process being 
 assisted by one or more men using long-handled shovels or forks to 
 keep the water and stones moving along and remove obstacles which 
 collect in the stream, as shown on Plate XIII, Fig. C. 
 
 The slope of the flumes must be carefully adjusted to maintain a 
 velocity sufficient to keep the material from being deposited. They 
 are continued on trestles out to the site of the dam and branches 
 
EARTH DAMS 
 
 217 
 
 are provided commanding the entire foundation. Gates or openings 
 in the sides of these flumes are provided at the necessary points for 
 discharging the water near the upper and lower faces where the 
 larger stones are needed. From these points the smaller stones and 
 fine material are carried inward toward the center of the dam. 
 Along the axis of the dam the muddy water is held temporarily in a 
 small pond in which the finer sediment is deposited thus forming 
 a water-tight core. 
 
 J Uhannel 
 ^460 (C..c.«.Il..d) ^ Drill Holes 
 
 Scale of Feet n Test Pits 
 
 ^° P 6£_H2_LSO c. Points of Control 
 
 -'^ Bock Outcrop 
 
 ft t Vitrified Drain Pipe 
 
 (Item 10 Schedule 1) 
 //////A Concrete Slope 
 
 Fig. 42. — General plan of Conconully Dam, showing location of spillway and 
 outlet works, Okanogan Project, Washington. 
 
 As a result of careful manipulation of the flumes the large rocks 
 are deposited on the outside of the dam, the smaller stones and 
 gravel inside of this and the finest sand and sUt in the center or near 
 the up-stream face. To bring about this result the flumes are shifted 
 inward on the dam as the structure increases in height; finally a 
 single flume deposits the last of the material on the crest, resulting 
 
218 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 in a symmetrical structure as shown on Plate XIII, Fig. D. The 
 general plan of the particidar work shown in this plate is given in 
 Fig. 42, this being the Conconully dam across Salmon River furnish- 
 ing water for the Okanogan Project, Wash. The area from which 
 the material has been taken by sluicing is shown on the hillside in 
 the lower part of the drawing, being nearly adjacent to the site of 
 the dam. 
 
 Among the objections to the hydraulic method of constructing 
 earth dams are those which arise from the limitations imposed by 
 the quantity of water available for sluicing the material, and the 
 difficxdty of elevating this or bringing it to the required height 
 above the dam to be built. In other words, there is usually not 
 sufficient elasticity in the limiting condition to meet aU of the 
 requirements, for example, it may be discovered after the work is 
 well opened up, that the best material to be utilized for the dam is 
 located a little too low to be effectively washed or the position of 
 attack must be changed, necessitating a reconstruction of the 
 conveying flume. 
 
 A more serious objection is that arising from the tendency of 
 material handled in this way to be sorted or stratified, for example, 
 if the work is not carefully managed, it may happen that for a brief 
 period sand may be washed into the dam and, due to the action of 
 the water, deposited as a thin layer. The finer particles or mud will 
 not penetrate this layer of sand and thus there is formed a line of 
 stratification or thin layers of different degrees of fineness, offering 
 opportunity for percolation or for sliding of one portion of the dam. 
 Another objection lies in the fact that if there is an imdue proportion 
 of fine clay in the center of the dam, this will not deliver its excess 
 water, except with great slowness, and remains a mass of unconsoli- 
 dated material liable to behave as a semi-fluid. 
 
 The principal benefit claimed for this method is the relatively 
 low cost of moving the material. When the conditions are favorable, 
 it is remarkably cheap, far less than the ordinary procedure by means 
 of plow, scraper, or hauling, but, as before stated, does not have the 
 adaptability of the latter. Some extraordinarily low figures have 
 been given of the actual cost of less than 5 cents per yard, but this is 
 where great quantities have been moved with a very conveniently 
 located bank of earth and with ample water supply. Under ordinary 
 conditions the cost is higher and for most localities the conditions 
 are so unfavorable that the cost is prohibitive. 
 
 Compacting the Material. — The proper compacting of the material 
 
EARTH DAMS 219 
 
 in an earth dam is one of the most important details of construction. 
 It may be done by simple or crude means. On smaller earth dams 
 built by hand labor or by plow and scraper the earth can usually be 
 compacted sufficiently by the trampling of men and animals. In 
 some cases, the dam has been enclosed with a suitable fence and 
 animals, bands of sheep, goats, range cattle, or horses have been 
 driven backward and forward over the area. 
 
 A more systematic procedure is to utilize a roller drawn by horses 
 or driven by steam or gasoline engine. The surface of the roller is 
 usually corrugated, or the roller may be made of rings moving 
 loosely upon an axle, so that each ring acts as an independent wheel, 
 settling Lato the inequalities of the surface. A smooth roller is 
 objectionable as tending to form distinct planes through which water 
 may seep. While the surface is being compacted it should be kept 
 moist. 
 
 Ramming by hand or by machinery is sometimes practised, 
 especially over small areas, particularly where a closure of an earth 
 dam is being made in a gap in the structure. Here, especial atten- 
 tion must be given to thoroughly compacting the earth and to the 
 details of forming a close bond with the adjacent slopes. Light 
 steam hammers have been utilized for rapid work in such confined 
 spaces to secure quick results. 
 
 Prevention of Seepage through the Dam.— The making of an 
 impervious wall or layer in an earth dam is a prime requisite. It is 
 relatively easy to put enough material in place to hold back the 
 water and to prevent the structure being washed away, but it is far 
 more difficult to arrange this material so that water cannot find its 
 way through minute channels or along contact planes. Primarily, 
 seepage is prevented by a proper selection and mixing of materials 
 and by compacting them thoroughly when deposited. There are, 
 however, a number of devices for securing impermeability, each of 
 these being used to greater or less extent, in accordance with the sur- 
 rounding conditions and especially the character of material available. 
 They may be classified as (a) core walls, (b) puddled core, and 
 (c) water-tight face. 
 
 Core Wall.— A core wall consists of a concrete, masonry, timber, 
 or metal wall or diaphram biult within the dam usually near its 
 center or toward the upper face and made as nearly impervious as 
 possible. (See Plate XIV, Fig. A.) It is usually thin (Fig. 43) 
 and is held in place by the adjacent mass of earth and rock. If 
 built of concrete or masonry it is founded, if possible, upon solid 
 
220 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 rock; where rock is some dis- 
 tance below the surface a nar- 
 row trench, is excavated to it 
 along the axis of the dam. 
 This trench is then filled with 
 the masonry or concrete. If 
 it is impracticable to reach 
 bedrock by digging the core wall 
 may be founded upon steel or 
 wooden sheet piling driven 
 sufficiently deep to penetrate 
 to an impervious stratum. 
 
 Instead of the concrete core 
 wall, the sheet piling may be 
 continued longitudinally up 
 through the dam by a stout 
 wooden or plank fence or bulk- 
 head made water tight by 
 sheathing or by plates of metal 
 suitably joined or riveted to- 
 gether. These extend through 
 the dam longitudinally from 
 side to side of the valley. An 
 objection to the use of a 
 metal or wood cut-off wall or 
 diaphragm in this connection 
 is the liability to deterioration 
 through the rotting or rusting 
 of the material. 
 
 All core walls are subject to 
 the further objection that the 
 earth or main body of the dam 
 in the course of settlement may 
 shrink or pull away or that the 
 wall may be ruptured by an 
 equal settlement thus leaving 
 plane of weakness or cracks 
 through which water may 
 percolate. It is very difficult, 
 if not impossible, to make a 
 good bond or tight joint between 
 
EARTH DAMS 
 
 221 
 
 the core and the material composing the main body of the dam. 
 It is held by some engineers that a thin core wall or diaphragm 
 should not be relied upon to produce water-tightness in an 
 earthen dam, but that it serves a useful purpose in preventing 
 animals burrowing through the embankment. Nevertheless, it 
 is believed there are some conditions where the building of 
 a thin core wall, especially of concrete and the holding of this 
 in place by earth and rock afford a satisfactory and econom- 
 ical method of construction. Such conditions have been met at the 
 earth dam closing the outlet of Strawberry Valley in Utah, the 
 section of the dam being given in Fig. 44. 
 
 ^ BWer Gravel and Olaj 
 
 Hounded Clue Limeetone fieuldeii 
 
 Toe Trenab\ Bolld Blue Limestone with Scainji 
 
 Out-off' Trench to Rock 
 
 Gore Vail to Solid Rook 
 
 Fig. 44. — Section of earth dam with concrete core wall and cut-off trenches, 
 Strawberry River, Utah. 
 
 Puddle Core. — Instead of attempting to make a tight wall or 
 diaphragm within the dam, it is practicable in most cases to secure 
 as good, or better, results by careful selection of fine earth or clay, 
 mixing this in proper amounts so as to secure a compact mud or 
 puddle impervious to water. Skill and judgment must be employed 
 in selecting, mixing, and placing the puddle, but if well done the 
 resulting condition may be preferable to the building of a concrete 
 or other core, because of the fact that the mass of the dam is more 
 nearly homogenous and settlement occurs without disrupting or the 
 opening of the joints or planes of seepage. An objection, however, 
 to the puddle core is that it may be penetrated by burrowing animals, 
 and if once punctured is eroded by the percolating waters. 
 
 Water-tight Face. — An impervious layer may under some condi- 
 tions be placed on the upper or water face of the dam to advantage. 
 This form of construction in many ways is more logical and conforms 
 
222 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 more to the theory of a dam, namely, of a water-tight wall or layer 
 held in place by suflScient material to prevent its being broken or 
 swept away. When this water-tight layer is put in the center as a 
 core wall it cannot be inspected, but if placed on the upper surface 
 it can be examined or repaired whenever water is drawn from the 
 reservoir. A water-tight face is, however, difl&cult and expensive 
 to construct and maintain. 
 
 To make this water-tight face, the simplest method employed in 
 small dams is by the use of inclined wooden covering or sheathing. 
 Planks are held Id place by suitable means and the joints closed by 
 battons or are caulked to form as nearly a water-tight sxu-face as 
 possible. In some instances sheets of iron or steel have been thus 
 used, being provided with expansion joints and carefully protected 
 from rusting by paint or various mixtures. Such metal covering is 
 held in place by steel beams, or by a backing of concrete or similar 
 material, and may be covered by a thin layer of concrete. The use 
 of wood or steel may be considered as more or less of a temporary 
 expedient, as the wood must be frequently renewed, owing to rapid 
 decay due to the rise and fall of the water and alternate exposure to 
 the waves and to the wind. The metal also corrodes, especially 
 at the joints where it is not always easy to secure perfect covering. 
 
 Cement or asphalt or a combination of both are occasionally used 
 for this water-tight layer, especially in small reservoirs for city 
 supply. The expense is prohibitory for larger works needed for 
 irrigation. 
 
 Care must be taken to provide adequate drainage for water which 
 may percolate into the center of the dam through these wooden, 
 metal or other coverings, and to see to it that the material composing 
 the mass of the dam is sufficiently pervious to let this water escape 
 without creating internal hydraulic pressure or uplift which will 
 tend to reduce the weight of the dam and permit it to slide. 
 
 Cut-off Trenches. — ^The cut-o£E trenches are located in the upper 
 portion and are made continuous with the core wall or less pervious 
 materials of the dam. Usually one cut-off trench is considered 
 sufficient, but conditions may arise where two or more may be 
 desirable. The trenches are planned and excavated in accordance 
 with evidence as to the character of the underlying material obtained 
 by the test pits or drilled holes. They are usually as narrow as can 
 be conveniently made and may be extended to an almost indefinite 
 depth, if upon opening up the material is found to be notably 
 pervious to water. In some cases, under earth dams, they have been 
 
EARTH DAMS 223 
 
 carried down to a depth of nearly loo ft. and then further extended, 
 as before stated, by driving sheet piling at the bottom. 
 
 In refilling the cut-off trenches great care must be exercised in 
 selecting the material and in packing it in place. Sufficient sand 
 or gravel should be included with the fine clay or other available 
 materials, to make a firm mixture, and one in which the voids will be 
 filled as nearly as possible. The resulting mass should be moistened 
 and tamped until thoroughly compacted. 
 
 In some cases, especially when the cut-off trench is carried to 
 rock, it is desirable to build in it a thin wall of concrete. If the 
 trench is very narrow and the walls of the excavation will stand 
 sufficiently long, it can be filled with concrete and the trench thus 
 used in place of wooden or other forms for holding the concrete in 
 place during the time of setting. 
 
 Protection of Slopes. — ^The slopes of the dam must be protected 
 from the erosive activities of the rain and wind. Any uncovered 
 bank of earth is quickly carved and corrugated unless well protected. 
 Such protection is afforded either by a pavement of stone or by a 
 growth of grass or plants whose roots hold the earth in place. 
 
 On the water side the protection must be of the firmest possible 
 nature, owing to the constant attack of the waves. As the water 
 rises and falls in the reservoir and especially at points where exposed 
 to the wind, the waves cut beaches or terraces and tend to leave the 
 banks of the reservoir in a series of horizontal lines. On the outside 
 or land side, the erosion due to the weather generally takes the form 
 of nearly vertical lines and here the less expensive covering may be 
 provided of turf or grass. 
 
 For the water slope, heavy stone or riprap is required. This 
 should be so placed that the stones interlock, and that the sweep of 
 the waves will not dislodge them. The foot of the slope must be 
 carefully arranged to sustain the weight or resist any tendency to 
 slide. The angle of the slope should be sufficiently flat so that the 
 stone pavement will rest upon it. This angle is dependent upon 
 the character of the underlying material. In the case of clay not 
 well drained, the water penetrating beneath the pavement on even 
 a relatively flat slope may cause the sloughing of the bank, carrying 
 with it the stone pavement. (See Plate XIV, Figs. C and D.) 
 
 On the dry side also, the character of covering is dependent 
 largely upon the material in the bank and plants and grasses selected 
 must be with reference to the angle of slope and constituent material. 
 
224 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 Drainage of Dam. — One of the elements of safety of an earthen 
 structure is in preventing saturation especially on the lower or land 
 side of the impervious layer or puddle core. It is assumed that the 
 dam may be saturated to this diaphram or core and that a small 
 amoimt of water will penetrate through it. This water and that 
 which falls in rain upon the surface must be quickly conducted away 
 so as to leave the lower side relatively dry and thus prevent the 
 tendency to slipping or sliding resulting from the presence of wet or 
 soggy material. In preparing foxmdations of the dam, drains must 
 be arranged and tile of suitable size placed longitudinally to the dam 
 in such a way as to catch and carry out to the lower toe any water 
 which may be percolating through the puddle core. At different 
 heights in the dam also other drains should in some cases be con- 
 structed for carrying the water out to the lower slope where it can 
 be caught in suitable gutters. 
 
 Dikes. — The term dike is applied to low, long earth dams, usually 
 built parallel to the general course of a river or along the shore of a 
 body of water to prevent the land from being overflowed by floods 
 in the river or by high tides or similar fluctuations in height of water. 
 
 H.W. 4092 
 
 Biprap to 83 
 
 Boiled 
 Embankment 
 8 Layers 
 Original Surface 
 
 XZ7 
 
 Scale 
 
 Fig. 45- — Cross-section of earth dike with pavement on water side. 
 
 The term dike is also applied to a long, relatively low extension of 
 an earth dam where the topography of the coimtry is such that the 
 dam must be continued for some distance across low grounds. It 
 frequently happens that in the prolongation of an earth dam the 
 topography is such that rising ground cuts out the necessity of the 
 dam or dike for a space of a few hundred or thousand feet and then 
 a depression occurs which must be closed by a low structure which 
 may be considered as a continuation of the main dam, in which 
 case the term dike is often used for each of these smaller earth 
 dams. 
 
 The principles of construction of dikes of this character is prac- 
 tically the same as those discussed for earth dams in general. One 
 
Pt.ate XT\' 
 
 nf^fmrnimsmm. 
 
 
 
 Fig. a. — Concrete core wall in earth dam. Carlsbad Project, N. Mex. 
 
 
 i'lG. B.- -Loose rock protection of earth dam on water side. Umatilla 
 
 Project, Ore. 
 
 (Facing Page 224.) 
 
Plate XIV 
 
 Fig. C. — Paving on water side of earth embankment. Belle Fourche River, 
 
 So. Dak. 
 
 Fig. D. — Concrete block protection against wave action on earth dam. Belle 
 Fourche Project, So. Dak. 
 
EARTH DAMS 225 
 
 or more cut-off trenches are provided and the water slopes paved, 
 as indicated in Figs. 43 and 45 and on Plate XIV, Fig. B. 
 
 Limits of Height of Earth Dams. — A few earth dams have been 
 built to a height of over 100 ft., but the majority of structures of 
 unconsolidated materials do not exceed from 50 to 70 ft. in height. 
 If carefully buUt, there is no reason for limiting the height, as it is 
 conceivable that earth may be so selected, arranged, and piled up 
 in such massive form as to form practically a range of hills or a 
 barrier comparable to that built by nature. The mechanical or 
 engineering difficulties are not great, but the limit to be placed is 
 that of cost, since the width or base of any high structure, especi- 
 ally one of earth must be correspondingly great. The cost therefore 
 increases rapidly with the height due to extra material which must 
 be selected and handled and the greater care required to prevent 
 defects in the work. 
 
 Examples of Earth Dams. — Of the higher earth dams some of the 
 more noteworthy are those recently built by the Reclamation 
 Service, the highest being that on the Belle Fourche project in South 
 Dakota, across Owl Creek, 115 ft. in height, and 6,200 ft. long, 
 containing 1,600,000 cu. yd. Also the dam on the Umatilla project 
 in Oregon, known as the Cold Springs Dam, 98 ft high and 3,800 ft. 
 long, containing 757,000 cu. yd. of earth and gravel and 32,500 cu. 
 yd., of rock fill. For comparison with these may be cited the 
 Tabeaud Dam in California, 123 ft. high, 635 ft. long and containing 
 370,350 cu. yd., also the San Leandro Dam in California, 125 ft. 
 high, 500 ft. long, and containing 542,700 cu. yd. 
 
 15 
 
CHAPTER XV 
 ROCK-FILL DAMS 
 
 Description. — A rock-fill dam consists essentially of a barrier or 
 embankment of loose rock with its up-stream face covered with an 
 impervious layer or blanket. It is the function of the rock portion 
 of the structure to resist the pressure of the water and hold in posi- 
 tion, against this pressure, the water-tight face, which in reality 
 forms the dam. 
 
 The rock section of the dam may consist of large and small stones 
 dropped or dumped into place with little or no attempt at systematic 
 arrangement, each stone being allowed to take its own position. 
 The width of base of the rock barrier is sufficient so that the weight 
 of the stones and the friction between them prevents any tendency 
 of the structure to overturn, or its parts to slide on each other. As 
 
 High Water 
 BplUTO f Cteat " 
 
 30 Trenoh to be Dug to/ 
 Bock and lUrUled ^ 
 
 (See SpecincatiotiB Par, ) Typical Section of £artli and'Bocb-Fni Dam 
 
 Fig. 46. — Typical section of earth and rock-fill dam, Clear Lake dam, 
 Klamath Project, Oregon. 
 
 compared to an earth dam, each component part or stone is relatively 
 large and heavy. It is, therefore, held in place by its weight and 
 also by the rough or angular projection of its neighbors. 
 
 The water-tight portion or face of the dam may be of various 
 materials, such for example, as wood, steel, concrete or earth. The 
 more common of these, especially for dams constructed during the 
 past few years, is earth; The thickness of this earth covering 
 is made to vary slightly, due to the character of materials available 
 and other local conditions. Its thickness also increases from the 
 top to the base of the dam as shown in Fig. 46. For high dams the 
 
 226 
 
ROCK-FILL DAMS 227 
 
 earth thus forms a considerable portion of the total materials re- 
 quired. Dams built in this manner, partly of rock and partly of 
 earth are commonly designated as rock- and earth-fill dams. 
 
 Advantages over Earth Dams. — The principal advantage of rock- 
 fill over earth dams is that the former is less likely to be injured or 
 washed away by overtopping during extraordinary floods or unex- 
 pected occurrences. There is also some advantage in the methods of 
 construction which may be employed, due to the fact that a limited 
 quantity of water can be passed through the rock portion of the dam 
 without serious injury. 
 
 If water rises in an ordinary earth dam, and finds a channel over 
 Of through it, the structure is doomed, as the component particles are 
 too small to resist erosion. Such a failure may be rapid, due to the 
 ease with which the earth is eroded and the flood thus let loose causes 
 great damage. A rock-fill dam on the other hand may pass a con- 
 siderable quantity of water over or through it without being washed 
 away, or even seriously damaged. Even though the earth portion of 
 the structure should be eroded and carried away through the loose 
 rock, there is a probability of the latter holding and reducing in a 
 great degree the magnitude of the flood. 
 
 In constructing a rock-fill dam, especially on a periodic stream, it is 
 frequently an advantage to deposit the rock, or a portion of it, in 
 running water, the earth or water-tight portion being built during 
 the low water or dry stage of the stream. The rock in this case is 
 dropped into the stream and partly washed into place, the slopes 
 adjusting themselves while the water is flowing over or through the 
 mass. This results in some waste of material, as there is a tendency 
 for the rock to be washed down-stream below the assumed toe of the 
 structure. Where plenty of material is at hand and cheaply moved, 
 this may be no serious disadvantage. It is also possible to construct 
 the water-tight portion of the dam in a stream of moderate size, by 
 first covering the upper face of the loose rock with small stones which 
 will be washed into the larger openings and then adding on top of this 
 successive layers of gravel, sand and finally clay or other fine-grained 
 material, thus forming an impervious blanket. This method of con- 
 struction also results in loss of earth, as some of the fine grains 
 are carried into or through the loose rock. Material, both earth and 
 rock, if deposited in water are as a rule more firmly compacted and 
 less liable to settlement than if built up dry. 
 
 Site to Which Adapted. — Almost any site suitable for an earth 
 dam is equally well adapted to one of the rock-fill type, provided the 
 
228 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 necessary materials for its construction are at hand. The most 
 favorable site is one with sufficient quantities of rock situated near it 
 and at sufficient elevation so that it can be shot down and easily 
 dumped into position. A soft bottom under the rock portion is not 
 always an objection, especially if the rock is placed in running water. 
 If the bed is soft, the larger rocks sink rapidly into it, the stream 
 scours out the lighter material and the mass is worked by the water 
 well into the foundation until securely held. 
 
 Foundation. — The remarks heretofore made relative to water- 
 tightness of the foundation for an earth dam apply equally for a 
 rock-fill one. The methods employed for preventing seepage under 
 the dam apply also in one case as in the other. That is to say, 
 a constituent part of the dam, such for example, ias a cuitain wall or 
 a trench filled with water-tight material should be carried down to an 
 impervious stratum such as rock or clay. 
 
 Wherever a rock-fiU dam can be built in the dry, that is, where 
 the foundation can be kept free from water during construction, 
 the site to be occupied by the dam should be prepared by removing 
 the lighter material. If a solid bottom can be reached, special 
 attention should be given to the water or upper side of the dam. 
 Here a cut-ofiE trench should be put down or sheet piling driven 
 if the underlying material is sufficiently permeable, the object 
 being to provide a continuous diaphragm or sheet of impervious 
 material extending from bedrock or from a heavy bed of clay upward 
 into the impervious covering on the upper face of the dam. Behind 
 or below this covering or blanket the stone should be arranged 
 to form as compact a mass as possible, filUng in the interstices 
 between the larger blocks with spawls and small stone but leaving 
 toward the lower side of the dam ample openings or drains for 
 taking away any water which may penetrate to the center of the dam. 
 
 Materials. — One of the most important questions for consideration 
 is that of obtaining economically a large amount of heavy stone 
 for the body of the dam. This can be had usually from the cliffs 
 or rock exposures which are to be found frequently on the sides of 
 narrow mountain valleys or gorges, through which a river has cut 
 its way. By undermining these in part or by placing explosives 
 in advantageous manner, large quantities of rock may be loosened 
 and thrown down in such position that they can be readily handled 
 and placed in the dam. The small stones can usually be had as a 
 result of the breaking up or moving of the larger pieces. 
 The size of rock used may be as large as can be handled by the 
 
ROCK-FILL DAMS 229 
 
 facilities available. In order to give stability to the structure, 
 the principal part of the rock-fill should be composed of stones 
 weighing each a thousand pounds or more. The spaces between 
 these large stones should be filled in with smaller ones. The upper 
 face of the rock embankment should contain enough small stones 
 and fine materials from the quarries to make it sufficiently tight 
 to hold the earth-fill in place and prevent its being carried into the 
 rock. 
 
 The gravel and earth covering, while it may be relatively small 
 in cubical contents, frequently necessitates relatively large expendi- 
 tures, as these must be carefully selected and placed. Where 
 rock is abundant suitable gravel and earth may not be easily obtain- 
 able but must be brought from a distance. In selecting the materials 
 for the earth-fill, the same, or greater precautions for water tight- 
 ness should be taken as in selecting those for an earth dam. When 
 a suitable mixture cannot be found in natural deposits, the materials 
 should be analyzed and properly combined. 
 
 Section and Slopes. — The most advantageous section for a 
 rock-fill dam, Uke an earth dam, cannot be determined by any known 
 mathematical formulae. It is known that dams of certain top width 
 and slopes have stood successfully, but how much their dimensions 
 might be reduced and still make a safe structure is a question which 
 cannot be positively answered. The essential requirement is that 
 the rock-fill shall be heavy enough to prevent sliding either upon 
 the foundation or within the structure. 
 
 The slope of the down-stream face should be sufficiently flat 
 to prevent any tendency of the rock sliding upon it or in other 
 words it should be less than the angle of repose for the material 
 used. The up-stream face of the rock-fill should be sufficiently 
 inclined to cause the weight of the water-tight covering to be sup- 
 ported largely upon it. This will prevent the tendency for cracks 
 being developed, due to unequal settlement. These conditions 
 are fulfilled by a slope of about i i/ 2 to i for the down-stream and 
 1 or I 1/4 to I for the up-stream face. Generally the up-stream 
 slope of the earth covering should not be less than about 3 to i. 
 
 The top width of the rock-fill may vary from 10 to 20 ft. .and that 
 of the earth-fill from 5 to 10 ft. depending upon the height of struc- 
 ture, and the distance below the top of the dam of maximum high 
 water in the reservoir. For very low dams where flood condi- 
 tions are not severe less top widths than these may be used with 
 safety. 
 
230 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 The up-stream slope, if of earth, should be protected from wave 
 action and from sloughing by means of suitable paving or other 
 covering. The down-stream slope generally needs no protection, 
 being composed of heavy rock. The rock in this slope may be 
 either hand placed or they may be dumped roughly to the neat 
 lines. Hand placing, while adding somewhat to the general 
 appearance, does not in any other way improve the work. In 
 fact, it is doubtful if a slope of hand-placed rock can be made as 
 durable as one of large stone dumped into position. 
 
 Water-tight Section. — ^There are various methods by means of 
 which rock-filLdams are made water-tight. Each of these methods 
 requires some form of water-tight face or section being placed on 
 the upper side of the loose rock-fill. 
 
 In the earliest examples of rock-fill dams a wood facing was com- 
 monly used. It was generally made of two thicknesses of matched or 
 tongue and grooved lumber held in place by being spiked to a timber 
 framework which was securely anchored into the rock. This form 
 of covering is not entirely satisfactory on account of the rapid decay 
 of the timbers and also its tendency to leak after a few years service. 
 Concrete facings have also been used to a limited extent. In these 
 there is a tendency for the concrete to crack, due to unequal settle- 
 ment in the dam. In this connection it may be well to state that no 
 structure built of unconsolidated material, such as earth or loose 
 rock is free from some slight settlement. This should be taken into 
 account in planning the work. 
 
 In the more modern construction of rock-fill dams a covering of 
 earth is commonly used on the up-stream side of the rock-fill. This 
 earth section is some cases in rendered more impermeable by means 
 of a puddle core of fine materials or by a core wall of concrete masonry 
 as shown on Plate XV, Fig. A. In some instances walls made of 
 metal plates have also been used in the body of the dams. Where 
 metal is used it is coated with asphaltum or some similar rust- 
 resisting substance and further protected from injury and corrosion 
 by being backed with thin walls of concrete. One objection which 
 has frequently been urged against the use of thin walls in a dam is 
 that they cannot be reached for purposes of inspection and repairs. 
 
 It is the opinion of the writers where suitable puddle material is 
 available that an earth section containing a carefully constructed 
 puddle core is the most satisfactory means of securing water-tightness. 
 Where a core wall is necessary on account of unsatisfactory materials 
 for the earth section, one of concrete either plain or with enough rein- 
 
ROCK-FILL DAMS 231 
 
 forcement to prevent cracking is believed to be the most satisfactory- 
 type. 
 
 Seepage through a rock-fill dam, on account of its greater stability 
 and more perfect drainage in the rock section, is not likely to prove as 
 dangerous as in the ordinary earth dam. Despite this fact however, 
 every reasonable precaution should be taken to reduce the seepage to 
 a minimum. 
 
CHAPTER XVI 
 MASONRY DAMS 
 
 Principles of Construction. — The masonry dam depends for its 
 stability upon the weight of its component particles, and also upon 
 the cohesive strength between these particles. It may be regarded 
 as a monolith of series of monoliths, each of sufficient weight to pre- 
 vent its overturning due to the pressure of the water and also having 
 sufficient cohesive strength between the parts to prevent sliding and 
 to a certain extent permit it to act as a beam or arch. 
 
 Comparing the masonry dam to earth- and rock-fill dams, these 
 may be arranged in a series according to the relative size and cohesive 
 force between the particles. At one extreme is the earth dam in 
 which each grain of earth or sand, or pebble of gravel, is infinitely 
 small compared to the total mass of the structure. These particles 
 are loosely held together and if exposed may be blown away by the 
 wind or washed away by rain or running water. The force of cohe- 
 sion, if regarded at all, is insignificant. 
 
 Next in such a series is the rock-fill dam, in which the pieces of 
 which it is composed as compared to those of the earth dam are 
 relatively large, many of them being of sufficient size to be com- 
 pared in a finite sense to the whole volume of the dam and so heavy 
 that they cannot be blown by the winds or washed away by running 
 water. With the masonry dam a further and last step in the series 
 has been taken in that the component pieces are cemented together 
 to form a single large mass, or at least to make a few blocks forming 
 an appreciable portion of the whole and each as a unit capable of 
 withstanding the force of the water against it. 
 
 In the masonry dam there is a factor of strength due to the condition 
 that a section of the dam is not dependent wholly for its stability upon 
 the weight of the component parts considered as loose particles. Any 
 vertical section standing along will resist a force tending to slide it 
 and also to a certain extent an overturning force by the cohesion of 
 its parts the section being considered to act as a monolith having 
 resistance to crushing and shear. Taking a horizontal section of the 
 masonry dam its strength is increased by each portion acting upon 
 
 232 
 
MASONRY DAMS 233 
 
 those adjacent to it which causes it to behave as an arch, if the 
 structure is curved, or to a certain extent as a beam or cantalever if 
 the structure is straight. 
 
 In designing a masonry structure, consideration is given therefore 
 not only to the weight of the material to be used, but to the form of 
 its arrangement and especially to the binding together of the parts 
 to resist the pressure brought against the whole mass and which tends 
 to overturn or Uft it. 
 
 Kinds of Masonry Dams. — Under this designation of masonry 
 are included all structures which are built of large or small blocks 
 or pieces, laid in some form of mortar or cement to cause the separate 
 pieces to adhere. There are thus included not only the dams 
 erected of carefully quarried and dressed stone with close-fitting 
 joints but also those built of rough fragments not dressed to specified 
 dimensions but which are carefully placed in mortar or cement 
 in such way as to form tight joints, the irregular intervals between 
 the large blocks being partly filled by smaller stones bedded in the 
 mortar. The large blocks may weigh many tons or the material 
 may have been crushed to small sizes, in which case, there results 
 a dam composed of concrete. The essential factor is that the com- 
 ponent masses, whether large or small, shall be carefully bedded 
 and surrounded or incorporated in mortar or cement, so as to form 
 a single mass. 
 
 An apparent exception may be noted where the masonry dam is 
 built with expansion joints or planes of weakness dividing the 
 structure into large sections, each of which is interlocked with its 
 neighbor but is of such size or shape, as to be able to stand alone — 
 acting as a separate pier or beam. 
 
 The typical masonry dam is one composed of carefully selected 
 rock, quarry dressed, and with outer covering or skin on the upper 
 and lower face, made of selected stones cut to dimensions such as 
 to form ashlar masonry. These stones or especially those on the 
 upper face resisting the water pressure are laid with extreme care, 
 so that there will be as little leakage as possible between the joints. 
 The interior of the section of the dam is usually composed of as 
 large stones as can be handled, laid carefully to avoid horizontal 
 joints, and having each stone well bedded against its neighbor, 
 care being taken to keep the top or working surface as rough as 
 possible in order that the tendency of slipping of parts of the struc- 
 ture along any plane may be avoided. 
 
 Rubble Concrete. — The masonry built of irregular masses of 
 
234 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 rock such as are obtained from the quarry, fitted into place without 
 any considerable dressing excepting to remove loose fragments 
 is included under the terms "rubble." For the construction of 
 large dams rubble carefully laid in mortar is not only more econom- 
 ical but is preferable to the ordinary dressed stone, because of the 
 fact that the joints between the rocks are irregular. If these joints 
 are carefully filled with mortar or cement the resulting structure 
 may be more nearly impervious to water. The dressing of the 
 stones from the quarry and attempting to bring them to flat sur- 
 faces not only introduces large expense but unless the work is very 
 carefully done, there is no resulting gain, so far as forming an impervi- 
 ous joint. The smooth surface introduces more or less of a plane of 
 weakness as compared with the rough surface where one stone 
 projects up into the space between others. 
 
 A typical rubble masonry dam is one in which the largest possible 
 stone and rock are used, these being put in place by derrick or over- 
 head cableways. The size of these may range from a ton up to 
 lo tons, or even 15 tons, dependent upon the strength of the machin- 
 ery. Each large stone is carefully inspected to see that it is sound 
 and that all of the loose fragments have been removed. It is then 
 thoroughly washed, before being swung into place. A bed of soft 
 mortar has previously been prepared and the large stone is placed 
 carefully in it, being lifted, if necessary, once or twice to see that 
 the stone bears firmly on all parts of the mortar bed- Spalls are 
 then rammed in, around or partly under the rock, where possible 
 and another bed is prepared alongside for a similar large rock, 
 these not being allowed to touch, but a space of two inches or more 
 is allowed between each projecting point. The result is what in 
 nature would be called a coarse breccia, in which the individual 
 fragments weigh tons, or what is sometimes called a "pudding 
 stone" in which the "plums" are large irregular fragments. For 
 the sake of appearances, such rubble structures are usually faced 
 with selected rock, or the projecting inequalities broken off, to 
 bring the structure within neat Hues, but even without such finish 
 the resulting work has a massive roughness consistent with its 
 general character. 
 
 The proportion of large rock in Cyclopean rubble is determined 
 largely by the question of expense. If the large pieces each 
 several tons in weight exceed about 12 per cent, of the volume 
 of the dam, the cost tends to increase, as it has been found that the 
 time required to make the joints is excessive and the apparent 
 
Plate XV 
 
 
 Fig. a. — Earth and rockfiU dam under construction, with low concrete core 
 wall, gravel and earth is being dumped on upper side with loose rock below, 
 Minidoka, Idaho. 
 
 Fio. B. — Concrete structure for regulating floods. East Park dam, Orland 
 
 Project, Cal. 
 
 (Facing Page 234) 
 
Plate XV 
 
 Fig. C. — Rubble masonry dam; lower portion of Roosevelt Dam, Ariz. (See 
 finished dam, Plate XI, Fig. D.) 
 
 Fig. D. — Foundations for Lahontan Dam, Nev.; showing concrete conduit, con- 
 veying water through lower part of dam, with conveying plant in background. 
 
MASONRY DAMS 
 
 235 
 
 gain in using the large rock is counterbalanced by the loss of time 
 in bedding them. 
 
 If distinctly stratified rock is used in the dam, especially any 
 pieces having a shaley structure, care should be taken not to bed 
 these horizontally, but to place the rock in the dam in a vertical 
 or inchned position so as to reduce the tendency to shear along 
 the horizontal planes. 
 
 Foundations. — On account of the great weight of a masonry 
 dam, the foundations must consist of soKd rock. There may be 
 exceptions where the masonry is of relatively small height and has 
 great breadth of base or bearing surface, in which case it may be 
 founded upon impervious clays or even on sand held in place by 
 sheet piling or even by round wooden or masonry piles. 
 
 In preparing the foundation, they must necessarily be laid bare, 
 the water being excluded by a cofferdam, or other means and all of 
 the looser and weaker portions of the rock removed. In case there 
 are open cracks or seams it may be necessary to excavate pockets or 
 shafts to a depth or extent such 
 
 as to clean out aU of the poorer 
 materials, filling in the cavities 
 thus made with carefully placed 
 concrete or masonry. The rock 
 in place after being stripped in this 
 way is left as rough as possible in 
 order to make a good joint and is 
 carefully washed to remove all of 
 the smaller particles and enable 
 the mortar to effect a complete 
 bond. 
 
 Section. — The cross-section of 
 a modern masonry dam has devel- 
 oped into a somewhat conven- 
 tional form following certain Fig- 47 —Typical section of masonry 
 general assumptions. On the dam, Boise Project, Idaho, 
 
 upper or water side the dam is nearly vertical, having in some in- 
 stances a light batter or forward projection of about i ft. horizontal 
 to 20 vertical. On the down-stream side, the slope is about i ft. 
 horizontal to from 1.5 to 2 ft. vertical. It is generally a straight 
 line, or may be gently curved, the batter or slope being increased 
 downward from about the middle height of the dam as shown in 
 Fig. 47- 
 
 Homonral Radius 662 
 Cl&Siiri 
 
 Maximum Cross Section 
 
236 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 This form of section has been developed from theoretical considera- 
 tions, verified by practical results. There are two principal forces to 
 be considered: first, the downward pressure, or weight due to gravity 
 of each portion of the dam acting upon the foundation or upon each 
 horizontal layer or section of the dam; and second, the horizontal 
 pressure or force of the water tending to push the dam down-stream or 
 overturn it. There are other forces, such as "uplift " and ice thrust, 
 of less immediate importance, but which are to be considered. 
 
 To compute the resultant of the two main forces, the dam is con- 
 sidered as consisting of an indefinite number of portions formed by 
 taking successively lower and lower sections from the top down to the 
 foundation. Beginning, for example, with the first lo ft. of the top 
 
 Fig. 48. — ^Location of dam and construction camp, Boise Project, Idaho. 
 
 section, the center of gravity of the assumed section, in this case 
 usually a rectangle, is taken and the downward force acting through 
 this center of gravity is computed. The horizontal pressure of the 
 water in the reservoir when full is also ascertained and shown as act- 
 ing upon a point in the cross-section one-third of the. height of the 
 water above the assumed base. The lines of force cross at right 
 angles. When graphically shown (Fig. 49) with length proportional 
 to the relative amount of pressure in each case they enable the con- 
 struction of a simple triangle of forces which gives the direction and 
 amount of resultant pressure. 
 
 This line of resultant force should evidently fall within the base 
 of the portion of the dam under consideration, otherwise the struc- 
 
MASONRY DAMS 
 
 237 
 
 ture might be overturned. In the earliest dams built the thickness 
 was as a rule made excessive and the resultant line fell far within the 
 section so that evidently there was a large waste of material. The 
 question as to where the resultant line should fall has been under 
 discussion among the engineers for many years, it being primarily a 
 question of the factor of safety to be used. There has finally been 
 adopted as more or less of a compromise a somewhat arbitrary rule 
 to the effect that the resulting line of pressure with the reservoir full 
 or empty should fall within the middle third of the base of each por- 
 
 FiG. 49. — Graphic computation of stresses in masonry dam. 
 
 tion of the dam. The accompanying Fig. 49 gives graphically the 
 analysis of pressures of the East Park Dam of the Orland project, 
 California, in which it is assumed that the weight of concrete is 140 
 lb. per cubic foot, the weight of the water, 62.5 lb., the weight of the 
 sand and gravel in river bed, 100 lb. per cubic foot. The only 
 stresses computed were those due to the dam acting as a gravity 
 section. The figures given at the bottom of each portion of this sec- 
 tion are the minimum and maximum vertical unit stresses per square 
 
238 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 inch for the reservou' full and empty. The general location of this 
 dam is given in Plate XV, Fig. B. 
 
 In addition to the ordinary static pressure of the water in the full 
 reservoir there should also be considered in the case of dams in north- 
 ern climates the probability of an increased pressure at the surface 
 due to the formation of ice on the reservoir. What this pressure may 
 be has not been determined. In many cases it is probable that it is 
 so small as to be negUgible. Observations on some of the large struc- 
 tures show that the ice against the dam is very thin, or in some cases 
 there is open water throughout the winter. The surrounding land 
 may be in such shape that the ice pressure if any is exerted along the 
 shore line and not appreciably against the dam. 
 
 The maximum amount of ice pressure that has. been assumed is 
 upward of 44,000 lb. per Unear foot. This adds notably to the 
 required thickness of the dam, and it has been questioned as to. 
 whether it is necessary or wise to make provision for such large 
 assumed forces. 
 
 Concrete. — The difference between rubble masonry and concrete 
 is one of size of individual stones rather than of essential difference 
 in kind. Instead of attempting to use the largest possible stones in 
 the structure, the pieces are crushed to a small and nearly uniform 
 size, and then mixed with the mortar or cement, so as to produce a 
 mass which can be readily handled by shovels or small tools or which 
 can be conveyed or allowed to flow into place through suitable 
 conduits. 
 
 One of the great advantages of concrete construction is that of 
 possible speed, the rate of depositing the concrete being dependent 
 upon the size and economical arrangement of the crushing, conveying 
 and mixing machinery which may be relatively compact; whereas, 
 in the case of masonry, including cyclopean concrete, the speed of 
 construction is often greatly reduced by congestion of the work and 
 necessity of installing bulky machinery in a relatively small space, 
 one operation interfering with or delaying another. With modern 
 methods of mixing and delivering concrete into place through con- 
 duits, it is practicable to keep flowing to the dam a nearly con- 
 tinuous stream without one portion of the work interfering with 
 another. 
 
 This speed of construction is an important consideration in the 
 building of dams in localities where work must be expedited between 
 flood seasons. By having made in advance suitable arrangements 
 of the material and machinery, it is practicable to lay a large amount 
 
MASONRY DAMS 239 
 
 of concrete in a constricted space far more rapidly and economically 
 than could be done in the case of large blocks of stone. 
 
 Another advantage possessed by concrete over ordinary masonry 
 is that the mass can be made practically homogeneous and the 
 stresses or strains in the finished structure may be more nearly antici- 
 pated and provided for by suitable expansion joints or other devices. 
 
 Upward Pressure. — No masonry or concrete structure is abso- 
 lutely impervious and it is necessary to assume that water will 
 find its way to a small extent under the foundations and into the 
 interior of the dam. In many of the modern structures elaborate 
 drains are provided to carry out to the lower side the water which 
 may thus occur as minute springs or points of moisture. In addition 
 to this certain allowances should be made in computing the strength 
 of the structure to provide for the accumulated lifting or over- 
 turning forces of the water which may percolate under or through 
 the mass and not freely escape at the lower side. 
 
 The amount of this upward pressure is dependent upon the height 
 of water against the dam. It is assumed to be maximum at the 
 water face and to decrease to nothing at the lower side. In com- 
 puting the overturning forces acting upon the dam allowance should 
 be made for the existence of this force and the thickness of the dam 
 correspondingly increased unless perfect drainage is provided. 
 
 Curved Dams. — Each section of the masonry dam is usually 
 computed as above noted on an assumption that it is to stand 
 alone, without aid from adjacent vertical sections, but wherever 
 the side walls or abutments are sufficiently firm and are not too 
 far apart, it has been the custom to design the whole dam on a 
 curved plan, so that it will act as a horizontal arch, transferring 
 the horizontal pressure of the water in part from section to section 
 and to the rock abutments. 
 
 The radius of curvature of this arch is generally from 400 to 
 600 ft. but may be more or less than this, in accordance with the 
 length of the dam. 
 
 Multiple Arch Dams. — In the types of dams already described 
 the force of the water is resisted by a solid mass of practically 
 uniform section throughout the length of the dam. In this way a 
 maximum of material is used and the question naturally arises as 
 to whether certain portions of the section of the dam cannot be 
 made thinner or, to consider it in another way, whether the retaining 
 wall Ar curtain cannot be held in place by piers or buttresses, rather 
 than by continuous mass of rock or earth. 
 
240 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 This is particularly the case with concrete construction, where 
 it is readily seen that the concrete dam being composed of more 
 or less plastic material may be moulded into any form desired. 
 The impervious blanket or curtain may be given a thickness only 
 sufficient to prevent percolation and can be held in place by but- 
 tresses or struts designed of ample shape and form to hold this 
 curtain against the pressure of the water. In other words, we may 
 design a structure upon thoroughly scientific lines and without 
 the unnecessary waste of material which is found in the usual solid 
 dam. 
 
 These multiple arch or composite dams are especially suitable 
 for conditions where economy of material is a prime requisite or 
 where the foundations are of a somewhat doubtful character. The 
 saving of the material is to a large extent offset by the difficulties 
 of construction and in many cases it has been found more satis- 
 factory to build the more simple, solid structure. There are, 
 however, a number of types of composite dams which are coming 
 into favor, in which the back or water-tight face of concrete, usually 
 reinforced, is supported by suitable concrete arches or pillars upon 
 a foundation or base adapted to the character of the underlying rock. 
 
 Internal Stresses. — In any structure where the masonry is laid 
 under varying conditions of temperature and humidity, there must 
 necessarily develop certain inequalities in loading. There is thus 
 developed strains due to these inequalities, for example, the masonry 
 laid during the extreme heat of summer when everything is expanded 
 must necessarily shrink during the extreme cold of winter. For this 
 reason, it is frequently specified that masonry structures in hot 
 countries, especially those portions where the section is relatively 
 thin, shall not be built during the time of greatest heat. 
 
 The largest stresses upon the masonry dam, especially on the thin- 
 ner portion near the top, are those due to daily change of tempera- 
 ture. During the clear nights when the radian is greatest, the 
 structure cools down and contracts. The morning sun may strike 
 upon one side of the dam, heating it rapidly, while the other side is 
 still cold, and by afternoon the conditions may be reversed, in that 
 the opposite side is exposed to the hot sunlight. Thus there is a more 
 or less continuous though minute movement of the structure and 
 tendency to form temperature cracks, due to alternate lengthening 
 and shortening of the structure. These intensify the action of 
 the waters percolating through the mass from the upper side, and 
 must be guarded against by increased thickness above what would 
 
MASONRY DAMS 241 
 
 theoretically be sufficient. The drying out of the mass of concrete 
 is also a very important factor in developing shrinkage cracks. 
 
 Safe Limits for Foundations. — The amount of load which a founda- 
 tion will sustain is dependent upon the texture and bedding of the 
 rock. A fine-grained granite, for example, with few if any visible 
 bedding planes and held in place by the weight of the adjacent strata 
 is practically incompressible and will stand almost any weight which 
 can be put upon it. On the other hand, porous volcanic rock or 
 strata with open seams may be readily compressed under the weight 
 of a mass of masonry. 
 
 It is customary to take samples of the material under considera- 
 tion for foundation as well as those of the rock to be used for the 
 structure and to apply crushing tests to determine the number of 
 pounds or tons per square inch required to fracture the stone. This, 
 of course, gives certain relative values for small samples of uniform 
 size and texture but does not demonstrate how the rock will behave 
 in large masses or when prevented from moving or expending later- 
 ally, as for example when in place and held by adjoining rock. 
 
 Based on the above assumptions the safe limits foi foundations and 
 for material for masonry dam have been taken as from 25 to 30 tons 
 per square foot or 400 lb. per square inch that is to say, in computing 
 the weight upon the foundations and in designing the thickness of 
 section of the dam, this has been increased until the pressure per 
 square foot of the superimposed mass wiU not exceed the figures 
 given. In this case, it is assumed that upon each square foot of 
 bearing surface there will be imposed the weight of a shaft i ft. 
 square and extending to a depth of the dam, plus the added pressure 
 due to the component forces which may tend to overturn the dam 
 and thus increase the pressure upon this point. 
 
 As a matter of fact, owing to the slight inequalities in bearing a 
 somewhat greater pressure may be imposed upon one square foot or 
 small area and correspondingly removed from another, so that 
 compression or crushing to a small extent must take place before 
 every square foot of the surface is brought into absolutely equal 
 bearing. 
 
 The data upon the strength of various rocks have been obtained 
 largely from tests made upon cubes of i in. or 2 in. on edge. These 
 show that under compression these cubes will withstand a weight 
 of from 20,000 to 40,000 lb. or even more per square inch, or from 10 
 to 20 tons. It is probable that in larger masses of indefinite extent 
 the ability to resist crushing would be still greater. With limestone 
 
 16 
 
242 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 likewise, the crushing strength for small cubes has been ascertained 
 to be from 14,000 to 20,000 lb. per square inch or from 7 to 10 tons. 
 Where the material underlying the foundation is relatively soft or 
 porous, the foundations must be spread correspondingly to distribute 
 the load, so that there can be no notable settlement after the struc- 
 ture is finished. Such settlements may result from either one of two 
 principal causes; first, the actual compression vertically of the rock 
 by which minute openings or joints are closed, or softer minerals 
 decreased in bulk or, second, by the gradual flow of some of the 
 lower layers. It is well known that even apparently solid rocks 
 under great stress are slightly plastic and if around the sides of the 
 foundations the rocks are not confined and held in place by adjacent 
 rocks of equal hardness, there will be a tendency to flow. If properly 
 held, however, even the softest rocks will sustain heavy weights as 
 shown, for example, by the action of partly consolidated sandstone, 
 or even of sand, which if held from lateral movement will sustain a 
 large load. 
 
 Overflow Dams. — Where the masonry is designed to be over- 
 topped by water, provision must be made not only for the increase 
 in water pressure against the dam but also for the increased weight 
 upon the structure due to carrying the water and also to the change 
 of distribution of load. The most important consideration, however, 
 is that of absorbing the energy of the falling water in such way that 
 it will not injure the dam either by direct erosion or by undercutting 
 of the toe or by impact or shock. 
 
 The^conventional type of overilow dam is that with gently curving 
 lower side on which the water overflowing the crest glides downward 
 over the smooth surface and is gently deflected from a nearly 
 vertical drop to a horizontal direction. The accompanying Fig. 
 50 gives the general outline of such a dam, together with the 
 graphic analysis of the stresses. In estimating the forces acting 
 upon the dam the assumption is made that the concrete weighs 
 147 lb. per cubic foot, that it contains 20 per cent, of rock and that 
 the weight of the rock is 156 lb. per cubic foot, the average weight 
 of the mixture in the dam being 149 lb. per cubic foot. The water 
 is assumed to weigh 62.5 lb. per cubic foot and the flowing mud 
 57 1/2 lb. per cubic foot additional. 
 
 The figure under discussion is a section of the Granite Reef Dam 
 on Salt River project, Arizona. It is provided with a tight concrete 
 curtain wall 6 ft. wide under the upper face of the dam, and another 
 curtain wall with wide holes to permit water to escape which may 
 
MASONRY DAMS 
 
 243 
 
 have penetrated beneath the dam. On the upper section the area 
 is estimated at 184 sq. ft. and the weight of a section i ft. thick is 
 given as 27,416 lb. On this the horizontal liquid pressure is esti- 
 mated at 24,750 lb., and vertical liquid pressure at 5,040 lb. 
 
 The curved section is designed on the theory that the water 
 should be forced to move in parallel lines down along the dam and 
 
 Assumed Hieb Water Elcv.1322 
 
 For ralllDElbodj 
 
 with Initial Ilarl£.nliKlt7 
 
 12>g ft. iMr Me a^d ;t = ZZ.5 
 
 y— 4u. CUpm aaa.f obL) 
 
 6 = abt.I5d en.Ct.par aai 
 
 l!^l «H^5a JOsllmft 
 
 — ? — U'- 
 
 Fig. 50. — Cross-section of overflow dam with graphic analysis of stresses, 
 Granite Reef Dam, Salt River Project, Arizona. 
 
 then be deflected to flow directly away from it. This theory is 
 followed out very well so far as the behavior of the water on the 
 face of the dam itself is concerned, but after the direction is changed 
 to a point where it should leave the dam, there is usually a retarda- 
 tion resulting in a standing wave which offers a number of curious 
 phenomena. The water, instead of continuing with gradually 
 reduced velocity down-stream, gathers in a mass on the apron of 
 
244 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 the dam and sets up a churning or rotary motion which threatens 
 to undercut the apron if near the lower edge. 
 
 Because of the difficulties involved by the standing wave or 
 whirlpool at the lower toe of the overflow masonry dams, this 
 type of dam has been made in many cases to depart from the con- 
 ventional curve and to drop the water more nearly vertically 
 rather than attempt to shoot it away from the dam in the horizontal 
 lines. In this case, it is necessary to make the cross-section of 
 the dam such that water flowing over the crest drops into a deep 
 pool or water cushion. In descending vertically it strikes the 
 return currents thus breaking up the force of water by work per- 
 formed upon itself. 
 
 Protection of Lower Toe from Erosion. — ^The vulnerable point 
 of most overflow dams is at the lower or down-stream toe. The 
 character of the protection of this determines largely the profile 
 of the lower side of the dam. If it is determined to deliver the water 
 into the stream in a horizontal direction it is necessary to provide 
 an apron extending down-stream for a considerable distance below 
 the dam. The length of apron required is of course dependent 
 upon the height of overflow and the volume of water passing over 
 the dam. The lower end of this apron in turn is usually protected 
 by heavy rock pavement, but even with the most elaborate device 
 there is liable to occur erosion of the bottom and sides wherever 
 there is a point of weakness. This is due to the whirling or gyratory 
 movement of the water set up in changing its velocity and cross- 
 section from that acquired by the fall over the dam to the relatively 
 slower movement in the horizontal channel. 
 
 Various arbitrary rules have been given for the length of the apron, 
 such, for example, that this should be five or ten times the height of 
 the overfall, but in most cases the apron has been built of what is 
 considered reasonably safe length, and then as experience is had, 
 it has been lengthened by protecting the lower end. 
 
 In the case of structures which are designed on the opposite 
 principle, namely, that of receiving into the stream channel the 
 water falling directly over the dam, an entirely different arrangement 
 is necessary. Instead of a smooth sloping apron a deep pool or 
 water cushion is provided with walls of sufficient strength to resist 
 the shock of the falling water. The theory of this form of construc- 
 tion is that the water should be forced to impinge upon itself and not 
 upon any hard substance. The container therefore must be of 
 sufficient size and strength so that the rotating or gyrating water 
 
MASONRY DAMS 245 
 
 in the pool will have sufficient volume to cushion the effect of the 
 fall without expending energy immediately on the walls. 
 
 Safe Heights. — The heights of masonry dams have been steadily 
 increased and larger structures each year are being designed on 
 the basis of experience attained in building and operating the 
 previously finished works. As in the case of ships or other structures 
 each decade appears to see the limit of size, but this is quickly 
 surpassed by the next design. Theoretically, there is no limit 
 to size, as a masonry dam is an artificial reproduction of a hUl or 
 dike, such as those built by nature to heights of thousands of feet. 
 It is merely a question of using enough material properly put to- 
 gether, the size being governed by the relation between the cost 
 and the value of the result. 
 
 With increase of depth and consequent hydraulic pressure upon the 
 natural cracks or pores in the foundations, and upon the joints in 
 the masonry, it is necessary to observe greater precautions both in 
 closing these cracks and in providing adequate weight and breadth 
 of foundation to afford an ample factor of safety. In building a very 
 high dam all of these matters are necessarily given greater study 
 and consideration than in the case of the smaller works. The 
 failures which have taken place have been of relatively low structures 
 in which the problems seemed so simple that they have been neglected 
 and the proper precautions have not been taken or the fundamentals 
 carefully worked out on a theoretical and practical basis as on the 
 higher structures. 
 
 Typical Masonry Dams. — The best-known masonry dams are 
 those which have been built in connection with the water supply of 
 large cities notably the dams on the Croton watershed for the city of 
 New York, those of the Sudbury River for Boston, and those in the 
 vicinity of San Francisco. More recently several notable structures 
 have been designed and built by the Reclamation Service, particu- 
 larly the Roosevelt Dam in Arizona and the Shoshone and Path- 
 finder in Wyoming. 
 
 The following list gives the location, name and t3rpe of the principal 
 storage and diversion dams, whether of masonry or earth, constructed 
 by the Reclamation Service, together with the maximum height, the 
 length and the volume of the dam in cubic yards. The largest 
 structure as far as cubical contents is the earth dam on the Belle 
 Fourche project in South Dakota across Owl Creek, containing 
 1,600,000 cu. yd. of earth. Next in order to this are the lower and 
 Upper Deerflat Reservoirs, Idaho, also earth banks, and then the 
 
246 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 Cold Springs Dam, also of earth, on the Umatilla project in 
 Oregon. 
 
 The largest of the masonry dams is that on the Salt River project 
 in Arizona, the Roosevelt, containing 342,000 cu.yd. of masonry with 
 a height of 280 ft. In comparison with this the Shoshone Dam in 
 Wyoming, with a height of 328 ft., contains only 75,000 yd. of con- 
 crete, and the Pathfinder, 218 ft. high, on the North Platte River, 
 in Wyoming, contains a little over 60,000 cu. yd. 
 
MASONRY DAMS 
 
 247 
 
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CHAPTER XVII 
 OUTLET WORKS 
 
 Capacity. — The capacity of the outlet of a reservoir or the means 
 of drawing down the stored supply, must be ample to provide for 
 the largest probable demand which will be made for water for irri- 
 gation and power purposes. In considering the size of outlet, ac- 
 count must be taken of the fact that it may be necessary to draw a 
 full supply when the water in the reservoir is low and the head on 
 the outlet comparatively small. For this reason computations for 
 capacity of outlet should be based upon a minimum head in the 
 reservoir. It is assumed that ample provision is made for a spill- 
 way capacity for floods but it may be desirable or even necessary 
 to supplement this spillway by large capacity of outlets because of 
 the fact that these draw water from the lower part of the reservoir 
 if not too deep, and thus aid to a certain extent in keeping it clean 
 by permitting the heavier muddy waters to escape. The spillways 
 skim off the surface of the less muddy water; if the flood discharged 
 is wholly over them, there is a tendency for the mud and silt carried 
 down by the floods to be deposited in the deeper part of the reser- 
 voir near the dam. Where practicable as much of this deposit as 
 possible should be drawn off through the lower outlets. 
 
 Location. — Experience has shown that outlet works for a deep 
 reservoir should be located at various heights. Where, for example, 
 the depth of water is considerably over loo ft. dependence should 
 not be placed wholly upon the sluices or gates placed near the 
 bottom of the reservoirs, as these are apt to be partly buried in mud 
 or silt. The erosive effects of the muddy waters under this head is 
 also so great that few materials can withstand it. In planning the 
 outlet works, therefore, arrangements should be made to draw 
 water under heads of not to greatly exceed 60 to 70 ft. and to use 
 the lower sluices only when the reservoir has been drawn down to a 
 considerable degree, or when it may be necessary to flush the lower 
 portion of the reservoir immediately adjacent to the dam. 
 
 The location of the outlet works must be governed largely by 
 consideration of the safety of the structure. Wherever practicable, 
 they should be built in tunnel in the natural rock of the side walls. 
 
 248 
 
OUTLET^ORKS 
 
 249 
 
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250 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 . Occasionally conditions are such that it is necessary to put the out- 
 let through the dam or on the foundations. In such cases extra- 
 ordinary precautions must be taken to prevent water following along 
 the outlet conduits or pipes, and to guard against any unequal 
 settling of the dam, due to this point of weakness. 
 
 Location of Gates. — The gates which control the outlet of a 
 reservoir should be so located that when closed they exclude water 
 from entering the conduit or channel through which water is to be 
 discharged. This is usually accomplished by locating the gates at 
 the upper end as shown in Fig. 51. If the gates are placed far back 
 in the body of the dam, the water standing against them when 
 closed exerts the fuU pressure of the reservoir head on the walls 
 of the conduit and may find entrance into the dam itself by per- 
 colation through these walls. For dams with flat up-stream slopes 
 the placing of the gates at the upper end of the outlet conduit 
 renders them more or less difficult of access. 
 
 The two conditions of accessibility and safety are combined with 
 difficulty and it is sometimes necessary to have more or less of a 
 compromise. As a rule, the gates are protected by being installed 
 within a solid masonry chamber as near as possible to the upper face 
 of the dam, the chamber waUs being projected upward into a tower 
 within which the necessary mechanism is located. The usual 
 practice is to provide the upper end of each outlet with valves or 
 gates in duplicate, so that if one set fails the other can be operated. 
 There is, however, opposition to this course, as it has been urged that 
 these gates may be multiplied indefinitely without eliminating all 
 risk of failure. In the recently designed Arrowrock Dam on the 
 ^pise River, Idaho, an exceedingly strong gate protected by a grill- 
 age is to be placed near the up-stream face to be used as a bottom 
 sluice and not to be opened under a head of over 60 ft. There are 
 also to be built in the lower portion of the dam several gates at vari- 
 ous elevations, each being supphed with an independent conduit. 
 Each of these openings can be closed by means of stop planks at 
 low stages of the reservoir and repairs made to the gates. By this 
 means they are rendered more accessible than would be the case 
 if placed in a tunnel. 
 
 Gate Towers. — ^Access to the gates controlling the outlets to reser- 
 voirs is usually provided by means of vertical towers or shafts 
 supported on top of the gate chambers and carried up above the high- 
 water level. Where the upper face of the dam is vertical, or nearly 
 so, as in the case of a masonry dam, the gate tower is usually built 
 
OUTLET WORKS 
 
 251 
 
252 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 against it. In some instances access to the gates is provided by 
 means of a shaft built in the body of the dam. This, however, may 
 introduce complications both of reaching and operating the gate 
 and possible unequal settlement of the structure. 
 
 For earth or rock-fill dams with flat upper slopes, the gate tower 
 is generally carried up as an independent structure, access to it 
 being provided by means of a bridge either from the shore or top 
 of the dam. In some cases inclined valves have been tried, such that 
 the operating mechanism lies along the sloping upper face of the dam 
 as shown in Fig. 52. A disadvantage of these is the difficulty of 
 operating and inspecting in this inclined position. In cold climates 
 some difficulty has been experienced, due to the pressure of ice 
 against gate towers constructed independent of the dam. The 
 strength which a tower must have to resist the pressure of ice under 
 varying conditions is difficult to determine with certainty. 
 
 Openings to gate towers are usually provided so that water may be 
 drawn from various elevations in the reservoir. Occasionally the 
 tower is divided into compartments so that water can be shut off 
 from one or other of the gates and drawn out, permitting inspection 
 and repairs. 
 
 Operation of Gates. — The gates or valves of low dams are operated 
 usually by a screw lifting device, the stem of the screw being con- 
 tinued upward through the masonry or within the tower to a point 
 above high-water level where sxiitable capstan or other mechanism 
 for raising and lowering the gates is installed. 
 
 Where the depth of the reservoir is very considerable, or over say 
 60 ft., vertical hydraulic devices have been successfully tried for 
 operating the gate, these being driven by small pump or motor. The 
 piston in this case is located as nearly as possible above the gates to be 
 raised and the piston rod operates through a stuffing box leading from 
 the top of the gate into a water-tight chamber immediately over the 
 top of the gates. 
 
 Erosion due to High Velocities. — ^Large gates or valves under high 
 pressure offer a number of problems and require special design. 
 The two chief points of difficulty encountered are, first, the 
 erosion due to water issuing through the gates under high velocity, 
 especially when carrying mud or sand, and second, the vibration or 
 chattering of the gates due to the current of the water passing over 
 the sharp edges, or around angular material. 
 
 There are some curious phenomena in connection with erosion. 
 On the one hand the hardest of materials may be rapidly cut by the 
 
Plate XVI 
 
 Fig. a. — Gate tower and bridge from earth dam, forming Cold Springs Reser- 
 voir. Umatilla Project, Ore. 
 
 Fig, B. — Grillage protecting entrance to gates. Pathfinder Jkeservoir. North 
 Platte Project, Wyo. 
 
 (Facing Page 252) 
 
Plate XVI 
 
 Fig. C. — Spillway with effective lengths increased by curved outlines. Orland 
 
 Project, Colo. 
 
 Fig. D. — Spillway for earth dam. Belle Fourche Project, So. Dak. 
 
OUTLET WORKS 253 
 
 sand blasts and the best concrete carved into fantastic forms; on 
 the other hand moss may be found growing on the edge of channels 
 where such velocities are obtained. The problem is largely that of 
 the character of the internal motions caused by the form of the 
 orifice. This is illustrated in the case of a jet or nozzle where it has 
 been shown that, for example, with a needle nozzle and with a certain 
 shape of bucket of water wheel, the water will issue in straight lines 
 and be deflected with the minimum erosion; whereas, with a slightly 
 differing form of outlet internal currents are set up, causing a large 
 amount of wear. 
 
 Experience has shown that the conduit leading away from any 
 large gate or valve operating under high pressure should have as 
 direct and straight an opening to the outer air as possible and with a 
 slight constriction beyond the gates so that the maximum pressure 
 will be borne by the outlet conduit and not by the gate itself when 
 wide open. 
 
 Vibration of Gates. — All forms of valves in which a portion is imder 
 tension are subject to serious vibration. For this reason the balanced 
 or needle valves with all the material in compression are preferable 
 wherever they can be used. The tendency to vibrate is reduced and 
 the wave movement is rendered practically negligible in well-designed 
 valves of this character. The cause of vibrations may be attributed 
 to three different classes of forces which when acting alone may be 
 negligible but when acting in unison produce serious results. Each 
 of these tends to cause a certain amount of motion, which may be 
 neutralized in part by the other but when by chance the time inter- 
 val happens to coincide the motion is amplified. 
 
 The forces causing vibration may be divided into three classes: 
 
 (i) Wave action. 
 
 (2) Pendulum action. 
 
 (3) Reed action. 
 
 (i) The wave action or rather the interval of action is that due to 
 the length of wave in the water. It is assumed that the velocity of 
 wave motion in the open air is 1,090 ft. per second. In the more 
 dense medium of fresh water, the velocity of the pressure wave is 
 generally taken at about 4,500 ft. per second in an open body of 
 water such as a lake, while a safe average in concrete-lined conduits 
 may be taken as 3 ,300 ft. per second. This pressure wave is set up on 
 the occiurence of a slight disturbance or motion of the gate and 
 continues indefinitely. 
 
254 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 (2) Any sliding gate hung vertically becomes in effect a pendulum 
 having a very slight range of swing. If this pendulum length happens 
 to coincide in some simple arithmetical relation with the length of 
 the pressure wave and thus the two happen to act in unison, the in- 
 tensity of the motion is increased. 
 
 (3) The lower edge of the partly opened gate being supported at 
 each side acts as a beam and the edge partakes of the nature of a 
 reed such as that of an organ but having an extremely low tone or 
 rate of vibration. This vibration following the laws of harmonics 
 may be synchronous at intervals with the pressure wave and pendu- 
 lum motion so that it may be conceivable that these three, namely, 
 the pressure wave, the pendulum wave and the reed wave may at 
 some interval occur on the same beat and their amplitude or destruc- 
 tive action be thus greatly increased. 
 
 Observation has shown that on structures even of great solidity the 
 opening of the gates to a certain point causes vibrations to be set up 
 and transmitted to a distance such as to be terrifying to the observer, 
 destructive to lighter machinery, and possible to the structure itself. 
 When, however, the gates are raised or lowered out of this particular 
 position, the vibrations are reduced and continue with more or less 
 magnitude, according to the dimensions and shape of the outlet. 
 
 This vibration or chattering of large gates under high head is 
 comparable in part to the action of the steam whistle, in which a 
 current of air or steam striking a thin plate or reed causes it to spring 
 forward, then it reacts backward through a minute space, these 
 alterations following with such great speed as to set up waves pro- 
 ducing sound. In the case of the gate, instead of the vibrating reed 
 we have a very large structure set in relatively slow vibration so that 
 each individual impact is noticeable. 
 
 The vibrations are dependent upon the degree to which the gates 
 are opened. As the gate is raised from its seat the motion begins 
 slightly and usually reaches its maximum with a half-opened or 
 three-quarter aperture, ceasing as the gate is pulled back into its 
 recess, unless the lower edge is fully exposed to the current of water. 
 
 The continuous vibration tends to loosen every joint and bolt, 
 finding every point of weakness so that in some cases it is necessary 
 to. open the gate completely or open and close it at short intervals, 
 in order to save the structure. The vibration when the gate is fully 
 open can be guarded against as before stated by having a constric- 
 tion in the solid conduit beyond the gate. 
 
 Character of Gates. — The lowest outlets for deep reservoir, 
 
OUTLET WORKS 255 
 
 especially where liable to be buried in sediment, should have rectangu- 
 lar slide gates without roUer or other complicated form of bearing. 
 It has been found advisable to use relatively broad, firm bearing 
 strips of composition metal somewhat of the character of bronze, 
 the two surfaces being made of slightly different composition for 
 the reason that if both bearing faces, namely that on the frame 
 and that on the valve, are identical in composition there is a tendency 
 to "freeze" in that the two metal surfaces of identical character 
 under this high head cohere probably through molecular action. 
 If, however, there is a slight difference in composition the molecular 
 structure appears to have sufficient difference to prevent this so- 
 called freezing. 
 
 These gates may be raised vertically by stems operated by oil- 
 pressure cylinders protected in such way as to prevent the entrance 
 of grit. The square form of gate has been found most desirable 
 as against the round seat, as this affords a more perfect sliding 
 surface and has less tendency to displacement when the gate is 
 partly open. For higher valves not buried in sediment various 
 forms of needle valves are preferable. All regulation of the full 
 reservoir should be done with valves of this character. 
 
 The lower slide valves or gates of the reservoir should never 
 be used for regulation but if necessary to open them they should 
 be drawn completely back into their sockets and not allowed to 
 remain in a partly open position on account of the excessive erosion 
 and vibration which is set up. The opening as before stated should 
 be into as nearly a straight smooth conduit as possible, gradually 
 changing from rectangular form at the gate to circular form and 
 lined both above and below the valve with cast-iron pipe arid con- 
 tinued by concrete sUghtly diminishing in sectional area until the 
 conduit is at least 25 per cent, smaller than the opening of the gate. 
 
 Where there are several gates each should open into a separate 
 conduit and these conduits should not unite but continue, each 
 independently to the outer air. 
 
 One of the important details of closure of flat-slide valves or gates 
 of this kind is in the character of the contact of the lower edge. 
 As this approaches the seat or bottom the scouring effect under 
 the gate is greatly increased and ordinary metal is quickly cut out 
 or destroyed. It has been found by experience that a relatively 
 soft seat composed of a bar of lead or even of timber if depressed 
 slightly below the floor will not be notably eroded and permits 
 the seating of the gate and complete closure even under high heads 
 
256 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 or unfavorable surroundings. The type of gate seat thus found 
 most advantageous is one where a groove is filled with a lead base, 
 the top of which is depressed slightly below the floor line. 
 
 In order to overcome the difficulties due to high heads a tj^ie 
 of balanced valve has been successfully used on several of the 
 reservoirs built by the Reclamation Service the general outlines of 
 which are shown in Fig. 53. The valve is easily operated by slight 
 adjustment of the pressure in the cylinder which carries the conical 
 plug or needle point, the destructive effect of the escaping water 
 being largely neutrilized by this form of orifice. 
 
 Fig. $3. — Balanced valve for regulating reservoir discharge under high heads. 
 Pathfinder dam, Wyoming. 
 
 Fishways. — Where diversion dams are placed in perennial streams, 
 it is usually required by state law that some form of fishway or 
 ladder be built so as to permit the fish to pass the obstruction. 
 The essential features are an inclined way on the slope of about 
 one in four, provided with compartments making a series of boxes 
 
OUTLET WORKS 
 
 257 
 
 T3 
 
 > 
 
 5 
 
 o 
 
 T3 
 
 ■a 
 
 
 -^W<-*-4-if4' 
 
258 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 open at the top. From the top down each is successively lower, 
 the water flowing from the higher into the lower down this slope. 
 
 A supply of water of at least 5 cu. ft. per second is usually neces- 
 sary to operate a fish ladder of this character. The water may be 
 allowed to spiU over the edges from one box or compartment to 
 the next and also a portion may flow through a small rectangular 
 opening in the lower corner of each compartment. These openings 
 are not placed in line with each other, but occupy successive alternate 
 lower corners of the partitions, so that the water entering one 
 compartment seeks the lower corner where it escapes through the 
 opening usually 8 in. high by 12 in. wide. It then flows diagonally 
 across the next compartment to the lower corner and so on, there 
 being formed a succession of pools in which the fish can rest, and 
 then dart through the submerged opening or they may leap over 
 the crest into the next pool as shown in Fig. 54. 
 
 The partitions are not arranged at right angles to the slope but 
 are incUned so that the water flowing through them will wash the 
 sediment into the lower corner and out into the next compartment. 
 For a dam 20 ft. high, the runway would extend 80 ft., and so on. 
 Care must be taken to have the lower end of the fishway brought 
 into the pool below the dam and into water where the fish will 
 readily find entrance. 
 
 SpUlway Reqiiirements. — A spillway consists of an opening or 
 space provided in or at the side of a hydraulic structure, such as a 
 dam or canal, and in such position that when the water rises above a 
 certain elevation, it will escape through this opening into a channel 
 from which it can be delivered usually to natural drainage line and 
 with the least injury or inconvenience. As a rule some form of 
 structure must be provided for a spillway, although in rare cases, 
 conditions may be utilized in such way as to permit water to escape 
 over the natural rock surface. Even in this case, however, it is 
 usually necessary to trim the rock and provide an artificially leveled 
 lip or sill over which the water may flow. 
 
 The first requirement is that the spillway shall have ample 
 length and capacity, so that before the water rises above the desig- 
 nated safe level, it wUl begin to escape in a broad thin sheet, and not 
 continue to rise rapidly to a height which will endanger the works. 
 Next to the width are the considerations of permanency and strength, 
 as a spillway may be called upon to handle large volumes of water 
 coming quickly during the time of extraordinary rains, causing 
 floods. 
 
OUTLET WORKS 259 
 
 Spillway Design. — The design of any form of spillway is largely 
 controlled by the surrounding conditions, more perhaps than in 
 many other structures in the irrigation system. In the case of the 
 storage dam the spillway location must be governed by the topo- 
 graphy and the design affected by the natural slopes which lead 
 away from the point of overflow. Sometimes it is almost impossible 
 to find a suitable point, and it becomes necessary to modify the shape 
 of the dam, lowering a part of the crest so as to provide a spillway 
 over one end, as for example, on the new Croton Dam for the City 
 of New York, where the right-hand end of the dam is curved up- 
 stream practically parallel with the side walls and prolonged in a 
 low lip over which the water pours into a broad flume cut in the 
 rocky side. A similar principle is used where a canal leading from 
 the reservoir is enlarged at its upper end, as in the case of the Avalon 
 Dam on the Carlsbad project, New Mexico. This permits taking 
 care of a part of the flood water by discharging it from behind the 
 dam into the head of the enlarged canal. It is there allowed to 
 escape by overflowing the masonry edge of the canal or let out 
 through large valves located in the bottom of a canal. 
 
 It is also desirable in some instances to design the spillway so that 
 it can be provided with automatic gates or flash boards arranged that 
 water can be held up on the spillway to the limit of safety. When 
 it rises rbove a certain point, the gates are opened automatically or 
 by hand. The simplest device of this kind is to build a small broad 
 bank or ridge of earth on top of the concrete or masonry spillway. 
 This for a time will hold back the water to a depth of say 2 or 3 ft., 
 but when it is overtopped the earth is quickly swept away, thus 
 releasing the excess water. 
 
 Deteiinination of Capacity. — The tendency in designing spillways 
 is to make them too small and in estimating the capacity required 
 to base the figures upon assumptions as to the usual flood condi- 
 tions. It should be remembered, however, that during the hfe of 
 the structure or during the coming century, there will occur some 
 one or more extraordinary combinations of rainfall or melting of 
 snow, which will produce floods, exceeding the previously known 
 maximum. It is to provide for these extraordinary conditions that 
 the spillway must be designed. For example, on Cache Creek, 
 a tributary of Sacramento River in California, the observations in- 
 dicated a maximum flood of about 20,000 second-feet, but from 
 various indications one of the engineers figured out a possible, 
 although improbable flood during earlier years reaching 60,000 
 
260 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 second-feet. This figure was generally regarded as almost absurd, 
 but upon the basis of these extreme assumptions, a spillway capac- 
 ity of 60,000 second-feet was provided. It was hardly finished 
 before a flood occurred, such as had never before been known, 
 with a probable maximum of 65,000 second-feet. Had not the 
 spillway been built of a size which was laughed at, the structure 
 would probably have been swept away. The lesson to be enforced 
 is that the engineer in such cases must be prepared for criticism 
 and ridicule by less well-informed people for buDding very large 
 and somewhat expensive spillway openings for structures, espe- 
 cially storage dams where there is a large catchment area upon 
 which storms may occur. 
 
 The determination of the size of the spillway must be based upon 
 a knowledge of the area which is drained and upon measurements or 
 estimates of floods which have previously occurred. It is essential 
 to study the rainfall records and the combinations of flood which 
 may arise from unusual storms occurring over one or another part 
 or the whole of the catchment area. 
 
 If, for example, the annual rainfall is 15 in. and the catchment area 
 consists of undulating plains and foothills, the ordinary discharge 
 following a well-distributed rain may be practically nothing at the 
 point of storage. Experience has shown, however, that the greater 
 part of the annual rainfall may occur in a few days and 6 or 7 in. of 
 rain may fall during one of these so-called cloud bursts. Where, 
 under ordinary circumstances, this rain would be distributed through 
 several weeks or months and would be lost daily by evaporation and 
 seepage, it now is brought together in the usually dry channels and 
 comes rushing down to the point of storage, creating a flood which 
 moves large boulders and overtops works which have stood perhaps 
 for several decades. 
 
 It is necessary, therefore, to assume these extreme conditions and 
 provide for a possible runoff of say 50 per cent, of the storm or for at 
 least 2 or 3 in. of rainfall over the area, even though this may not 
 occur more than once in a lifetime. 
 
 Location and Type. — Wherever practicable, the spillway should be 
 located away from the dam or principal structure which it is designed 
 to protect, in order to guard against any backcutting or other de- 
 structive action due to the passage of a great volume of water during 
 a short period. It is frequently necessary, however, on account 
 of the topography of the country to construct the spillways as part 
 of the masonry dam, and to permit the waste water to flow into the 
 
OUTLET WORKS 261 
 
 stream channel immediately below the dam. In such case provision 
 must be made against the water backing up against lower toe of the 
 dam and by the gyratory motion of the water undercutting or weak- 
 ening the foundations. In the case of earth dams, it is particularly 
 important to place the spillway upon rock, or the most solid portion 
 of the undisturbed ground protecting this with pavement of rock or 
 concrete in such way as to prevent cutting. 
 
 The type of spillway is governed by the topography of the country. 
 It is usually possible to find a depression in the rim of a reservoir 
 which may be enlarged or modified in such form as to provide a lip 
 or sill of several hundred feet in length. In some cases, as that at the 
 Shoshone Dam, Wyoming, where the works are in a narrow canyon 
 with almost vertical walls, it has been necessary to provide a spillway 
 discharging through a tunnel around the end of the dam. It was not 
 considered safe to allow the water to pour over the top of this struc- 
 ture 327 ft. high. In this case, a large funnel-shaped opening has 
 been provided with a broad curved lip, 1 5 ft. below the top of the dam, 
 the water pouring over this lip falls into a depression in which it con- 
 verges to enter the tunnel where with a velocity of upward of 20 ft. 
 per second it passes through the opening in granite walls out well 
 below the toe of the dam. 
 
 Grades and Velocities. — In every spillway device the object is to 
 take the water away as rapidly as possible, consistent with safety, 
 and therefore the maximum allowable grades should be provided, so 
 as to reduce the size of th,e channel to be made. If the discharge is 
 over a granite or similar hard rock, the spillway may consist of a 
 series of falls or rapids. If through softer materials such as shale, it 
 may be necessary to line the channel with concrete and reduce the 
 grade to prevent the excessive velocities wearing out the lining. As 
 a rule, the large spillways are only called into use once or twice a year, 
 or perhaps only once in a decade, and then for only a few hours or 
 days, so that such erosive forces are not indefinitely continued. It is 
 therefore, practicable to take larger chances on erosion than would be 
 the case with structures in continuous use, that is to say, after a large 
 flood there will usually be an interval of months of even years during 
 which any small damages may be repaired, so that it is perfectly 
 proper to assume the probability of small injuries. On the other 
 hand, it is extremely dangerous to incur any risk which may take 
 place during a large flood, creating an injury sufficient to disturb the 
 structure and to release the stored water behind the spillway. 
 Protection against Erosion.— The most effective protection against 
 
262 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 erosion is by suitably placed masses of masonry or lining of concrete 
 as shown on Plate XVI, Figs. C and D. In some cases, logs or tim- 
 ber may be used to protect the softer rocks or points of weakness, 
 as this timber, although it may be warped by the sun, will afford 
 enough protection during the short duration of flood to prevent 
 injurious action. 
 
 The concrete lining of a spillway section may be dispensed with 
 in part by building a series of drops or pools, although it is generally 
 found to be more economical to line an inclined chute with a rela- 
 tively thin mass of concrete than to attempt to concentrate the fall 
 in a few places by using heavy structures. 
 
CHAPTER XVIII 
 WATER RIGHTS 
 
 Definition. — A water right may be described as tlie ownership or 
 claim which has been sustained by the courts or some form of action 
 by suitable state officials by which there has been established the 
 right to the use of a certain quantity of water. This is usually 
 limited by seasons or periods of the year, that is to say, the right 
 to the use of water taken from the common stock, is limited not 
 only in quantity, but also in duration, being as a rule confined to the 
 crop-growing season. There are, however, water rights out of the 
 crop season which may be utilized for purposes of storage in reser- 
 voirs and in some cases the claims are made that the rights are to 
 possession of a continuous flow of water at all times, irrespective 
 of the season. 
 
 The term water right is often used loosely to imply simply the 
 claim to the right to use water and not to the actual established 
 right. For example, it may be said that a certain water right in- 
 cludes the entire flow of a given stream, meaning by this that the 
 claim is made that the entire flow belongs to or is appurtenant to 
 certain described tracts of land. The distinction should be made, 
 however, between the actual rights as properly established or con- 
 firmed and those which are more or less vague and arising simply 
 from notices posted or entered upon the county or state records 
 and which have not ripened by process of law into actual rights. 
 
 The engineer having determined from the physical standpoint 
 that there is an adequate supply of water for the proposed irriga- 
 tion works, must give careful consideration to the question as to 
 whether the rights to the use and control of this water have been or 
 can be properly guarded. Many an engineering work otherwise 
 successful has been a failure because of neglect of this precaution, 
 as, for example, where an engineer has made his plans with reference 
 to the given volume of water which he has found to exist, but, to 
 his astonishment, has later found that the title to this has been so 
 insecure that his works have never been able to operate successfully. 
 
 The legal and engineering questions relating to water rights 
 merge in such way as to be practically inseparable. This is because 
 
 263 
 
264 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of the fact that water occurring in nature in fluctuating volumes is 
 not susceptible of exact limitation by metes and bounds, as is real 
 estate and it is not possible to establish accurate lines of division in 
 the same way that farm boundaries can be laid out upon the ground. 
 In the case of a stream which on one day is carrying 300 second-feet 
 and on another 30,000 second-feet, and on which the claims to the 
 water at the various points along its course may aggregate 1,000 
 second-feet, the problem of exact limitation of the quantity avail- 
 able to each of several hundred claimants is a mixture of physical 
 and legal problems which can be solved only by the engineer and 
 lawyer working together, each having a fair comprehension of the 
 technical requirements of the other. 
 
 The proper acquirement of the rights to the use of water and the 
 perpetual protection of these are among the most vital points in 
 the planning of any irrigation project or system. While it is not to 
 be supposed that the engineer or businessman having to do with 
 irrigation works is fully versed in the details of irrigation law, yet 
 it is necessary that he have such knowledge of the fundamental 
 facts and sufficient grasp of the general principles to be reasonably 
 certain that the rights involved are adequate. At least, he should 
 have such general knowledge of the dangers as will lead him to call 
 for the best procurable legal advice upon the points involved. 
 
 The method of determination of the rights to the use of water 
 and the operations or practices are by no means uniform nor certain. 
 The whole subject of water law as pertaining to irrigation is still 
 in a state of evolution and every important point should be thor- 
 oughly questioned and carefully considered in advance of entering 
 upon any new scheme. 
 
 There is great apparent contradiction in court decisions on 
 fundamentals and their application, so that no important point should 
 be assumed as established until thoroughly examined and passed 
 upon by competent authorities. 
 
 Origin of Water Rights in the United States. — Water rights in the 
 arid western states of the Union are derived primarDy from the 
 original federal ownership or authority, as nearly all of the arid 
 lands formerly belonged to the United States. These lands have 
 been or still are at the disposal of Congress and for the most part are 
 open to settlement under the homestead laws. With the ownership of 
 the arid land was included also the ownership of the waters originat- 
 ing in the mountains or elevated plateaus of the national domain. 
 
 One of the conditions attached to the disposition of the arid 
 
WATER RIGHTS 265 
 
 areas, notably under the terms of the Desert Land Act, is to the 
 effect that they must be reclaimed by the use of waters taken from 
 the streams, and applied to the soil, the water thus taken not being 
 returned to the water course. 
 
 This requirement of taking water from the rivers enacted into 
 law by Congress, is a recognition of the common need of the country 
 of the diversion of the streams to irrigate the arid lands. It also 
 illustrates the fact that the riparian ownership of water as embodied 
 in the common law of England and in the statutes of the eastern 
 states is not applicable to the needs of the people of the arid regions. 
 
 Under the theory of riparian rights each owner along the natural 
 stream enjoys the right to have this stream flow in its natural state 
 practically undiminished in quantity, and unchanged in quality. 
 This is in accordance with the common necessities of a humid region 
 where there is usually water in excess and where no one man should 
 be allowed to interfere with the natural behavior of the stream to the 
 detriment of his neighbors. 
 
 In the arid region, however, this "let alone" policy is obviously 
 impracticable. The lands cannot be put to their best uses without 
 taking water from the stream. This water, if put to beneficial use, 
 cannot be returned to the stream, and hence the flow of rivers must 
 be systematically diminished and finally the beds will become nearly 
 if not quite depleted if the arid region is to be reclaimed. The time 
 is rapidly approaching when in the lower courses of the natural 
 streams there should be no water left, excepting possibly in times of 
 unusual floods. If water is thus found, it may be considered as an 
 indication of poor management or imperfect control of the natural 
 resources of the area. 
 
 The generally accepted theory that water in a natural stream is the 
 property of all of the people is based on the fundamental fact that 
 it is essential to all life, both animal and vegetal. In distinction 
 to natural streams, however, are the waters which occur in springs 
 or wells upon certain tracts of land and which are considered as 
 belonging to the owner of that particular tract of land. With the 
 proprietorship in springs may be classed also certain waters taken 
 from a natural stream and put in an artificial reservoir. When thus 
 severed from the common ownership such waters become the prop- 
 erty of the owner of this reservoir, and are no longer subject to the 
 rules governing flowing waters. 
 
 In some of the western states, the claim is occasionally made 
 that the natural waters belong not to the people but to the state 
 
266 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 and that the state may dispose of these waters in accordance with 
 law. But, it is more generally held that the control of the state 
 arises not through actual ownership, but throu'gh other powers. 
 It is universally recognized that the state must have such direct 
 control over the distribution of the waters to the claimants as will 
 insure an orderly use of these and prevent discord. 
 
 As there is not sufficient water in the arid region for all purposes, 
 the great question next to that of ownership is as to who shall 
 take from the common stock and who must be denied the water 
 which is necessary for life and for crop production. A rule generally 
 recognized is that of first in time is first in right, but this must 
 again be modified by other considerations, as the first man who 
 takes the water may desire to use it in ways not wholly in accordance 
 with the common good. Thus have arisen the superior claims for 
 water needed for the sustenance of life, that is, for domestic purposes, 
 for cattle, and for municipalities as being prior to all others. Next 
 comes agriculture, or the needs of crops produced for food to sustain 
 life, then manufacturing or industrial purposes, as less important 
 than the fundamentals of drink and food. 
 
 Having settled that priority of appropriation and use shall 
 govern and that within these priorities there are certain superior 
 needs, the next broad question is that connected with considerations 
 of waste of water. On this point, the most generally accepted 
 rule is that which has been incorporated in the Reclamation or 
 Newlands Act of June 17, 1902, which states "that the right to 
 the use of water acquired under the provisions of this act shall be 
 appurtenant to the land irrigated and beneficial use shall be the 
 basis, the measure, and the limit of the right." This embodies 
 two distinct and fundamental ideas vital to the proper use of the 
 common fund of water. First, of appurtenance to the lands irri- 
 gated, and second, of beneficial use. 
 
 The appurtenance to the lands irrigated means that when water 
 has been appropriated for a certain tract of land, the water needed 
 for this land goes with it and is not held separately in a way such 
 that the land may be deprived at some future time of the necessary 
 supply. The importance of this principle is not dependent wholly 
 upon the need of the particular tract of land under consideration, 
 but is in recognition of the fact that other rights grow up in time 
 such that if water is not used upon this particular piece of land, 
 but should be transferred elsewhere, confusion would ensue with 
 a consequent loss directly or indirectly to other lands. 
 
WATER RIGHTS 267 
 
 The second and perhaps more important rxUe is that of beneficial 
 use. Usually, the law does not attempt to state in engineering 
 terms how much water shall be used on any tract of land, but limits 
 this by the broad definition of beneficial use. At first, a certain 
 40-acre tract may reqtiire a large amount of water, while the sub- 
 soil is being filled and the surface subdued or filled with humus. 
 At a later time, with increase of irrigation in the vicinity and with 
 the changes which follow, a very small amount of water may be 
 applied to the surface and sometimes none at all throughout an 
 entire crop season. The rule of beneficial use works automatically 
 in that, if water is not actually needed for this particular tract, 
 none may be successfully claimed. 
 
 Riparian Rights. — Under the term riparian rights are included 
 those claims to adjacent waters established by usage or by judicial 
 processes under which the owners of land adjoining a stream enjoyed 
 the direct or indirect use of these waters. These riparian rights are 
 generally limited in such way that the abutting landowner may take 
 some of the water for domestic use or for cattle or for manufacturing 
 and other industrial purposes but his rights are limited by those of 
 the entire community. These usually require that the water be left 
 practically undiminished in quantity and unpolluted or otherwise 
 changed in quality. 
 
 The doctrine of appropriation and priority of use has been gen- 
 erally adopted throughout the arid part of the United States. This 
 is in direct opposition to the principles governing flowing water which 
 are embodied in the laws and court decisions of the eastern or humid 
 states. Within these the so-called riparian rights prevail, being 
 adopted from English practice. 
 
 Riparian rights are founded upon the theory that there is enough 
 water for every ordinary purpose and to spare, and that the flowing 
 water cannot be diverted to the exclusive use of any one, excepting as 
 far as ownership of the lands along the banks may permit such di- 
 versions. Each landed appropriator bordering upon a stream must 
 permit the flow to continue practically undiminished in quantity 
 and quality. He may take it out upon his own land, but he must 
 return it after having put the water to use for power, or for other 
 purposes. The enforcement of any such doctrine is, of course, 
 directly antagonistic to the common needs of the people of the arid 
 region where the lands have little if any value excepting by the use of 
 the water taken from the streams. 
 
 The riparian law was founded upon the common needs of the people 
 
268 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 of a humid region. It was the outgrowth of practical or common 
 sense as applied to the daily problems. In England it has been 
 modified from time to time according to the conditions of develop- 
 ment of the country and the larger needs of the people but in the 
 humid parts of the United States, the riparian doctrine has become so 
 crystallized into law and so rigid in application that to a large extent 
 it has not been conducive to the largest possible development of 
 water. 
 
 In the arid regions the riparian rules are not wholly applicable, as 
 there the common needs of the people are dependent upon taking 
 water away from the stream, using it and returning little, if any, to 
 the natural drainage. On the extreme western border in California, 
 a state partly humid, the system of laws originally adopted by the 
 Americans were copied from those of the eastern humid states and 
 included the ideas of riparian rights. In the arid portion of the state, 
 however, especially near the old Missions, there grew up in accord- 
 ance with the needs of the people, the recognition of the Spanish 
 theory of appropriation and use of waters. Thus these two antago- 
 nistic principles came into conflict as the state was developed. 
 
 The result has been innumerable controversies and court decisions 
 which at one time appear to favor riparian rights, and at another 
 the necessary rules of appropriation. Neither has yet been definitely 
 and conclusively established as against the other, but there appears to 
 be a tendency to interpret the riparian rights in accordance with 
 beneficial use, that is to say, if a riparian appropirator has put the 
 water of a stream to beneficial use either for watering his cattle or for 
 irrigating his land, he wUI be protected in this, but he may not neg- 
 lect to use the water indefinitely and then at some future time demand 
 his riparian rights to the destruction of valuable improvements and 
 irrigated lands above or below him. 
 
 It is essential that the engineer in planning his works know some- 
 thing of the extent of the riparian rights which may be claimed upon 
 the streams. He should receive definite assurance that such rights 
 do not exist, or are limited and that he may depend upon the rules 
 of appropriation for the water supply needed for success. 
 
 Acquisition of Water Rights. — Starting with the proposition that 
 the Federal Government permits and requires the diversion of streams 
 on the public domain for reclaiming desert lands, as a requisite to 
 obtaining title to these, it has followed that as new states are created 
 within the arid regions and duties of providing systematic methods 
 of administration are prescribed, these newer states of necessity 
 
WATER RIGHTS 269 
 
 have been forced to consider the orderly distribution of the waters 
 and the adoption of certain broad fundamental rules. As previously 
 noted, in most of the state constitutions of the arid region, it is 
 recognized that the waters belong to the people. In some of the 
 states the phrase is used in such a sense as to imply that they belong 
 to the state but this ownership by the state is obviously not the char- 
 acter of ownership by which the state may sell or dispose of these 
 waters or deal in them as it might in lands or buildings. 
 
 Assuming as true, the fundamental proposition that the waters 
 belong to the people, next comes the recognition of the fact that as 
 there is not enough water for all of the people and there must be 
 some orderly system for distributing these and for giving to certain 
 persons an exclusive right or an artificial monopoly. This is gener- 
 ally done in accordance with the rule that a man first in time is 
 first in right. If the first-comer should claim everything in sight 
 there will be nothing left for the next man. It follows that it is neces- 
 sary to modify this rule by another, namely, that the man first in 
 time shall be limitfed to an amount of water which he put to beneficial 
 use. Otherwise, he might file claims, as many pioneers have done, 
 to the entire flow of the river, proceed to divert a small percentage 
 of it and try to hold the rest for speculation profit. 
 
 In determining officially the amount to which each claimant is 
 entitled, it is necessary for him to show that he put the water to 
 beneficial use to a certain extent prior to a certain date, or to the 
 time when others also utilized portions of the water. This is em- 
 bodied as before pointed out in the latter part of the provision in 
 the Reclamation Act to the effect that " the right to the use of water 
 shall be appurtenant to the land irrigated, and beneficial use shall 
 be the basis, the measure, and the limit of the right." 
 
 The methods of acquiring water rights are variable; each of the 
 states has its own system or lack of system in the matter. In general, 
 it may be said that all of the states recognize rights as acquired by 
 actual construction of works and by the application of the water 
 to the land or by exercising due diligence in making such applica- 
 tion of the water. In some of the states a regular system is provided, 
 namely, of applying to a state official, usually the state engineer, 
 for permission to divert a certain stated amount of water for irri- 
 gation for a definite tract of land. It is supposed to be the duty of 
 this official to ascertain whether there is actually water available 
 for appropriation. To do this he takes into consideration what is 
 known of the flow of the stream and of the appropriations already 
 
270 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 made. If he is satisfied that there is water which as yet has not been 
 appropriated, a permit is issued. If work is pursued with diligence 
 and proof is made of actual reclamation, the right then becomes 
 established. 
 
 In case of shortage the prior appropriators receive their full supply, 
 and the later appropriators receive what is left, each in the order of 
 the date of the official records. 
 
 In other states, where an orderly or business-like system has not 
 been developed, it is customary to post notices of appropriation 
 along a stream or at the point of proposed diversion of the water, and 
 to make this notice a matter of record within the county. Thus, as 
 developments proceed to a point where there is scarcity of water and 
 controversies arise, it is necessary to bring the whole matter into 
 court, and to settle relative rights according to the testimony of the 
 older inhabitants. 
 
 This has proved an expensive and dilatory process and in some 
 counties it has been asserted that the expenses of litigation are greater 
 than those of construction. For example, "A" may bring suit 
 against " B " to settle their relative priorities, and " B " against " C," 
 and so on, with infinite combinations, and when all have been ex- 
 hausted some successors to older and apparently abandond claims 
 X, Y, or Z, may bring suits individually or against collective 
 groups, and get the whole matter again into court. Wherever 
 practicable, the attempt is now made to include in one suit all of 
 the possible claims on the river and its tributaries, and in some in- 
 stances in order to settle relative rights, suit has been brought against 
 upward of 4,000 individuals. 
 
 The recognition of the necessity of an orderly and systematic 
 procedure in establishing rights to the use of water has not yet 
 reached the point of completeness in the United States comparable 
 to that attained with reference to land titles. While great care is 
 exercised in verifying every point with reference to title to a farm, 
 there still exists a relatively chaotic condition with reference to the 
 water which in many localities alone gives value to this land. We 
 are still in many parts of the country in what may be called a medie- 
 val condition as regards titles to water, one where each man claims 
 everything in sight and the aggregate of the claims exceeds by many 
 times the amount of water available. With the rapid development 
 of a higher standard of public or civic morals must come the recogni- 
 tion of the necessity of simple and comprehensive methods of secur- 
 ing titles to the use of the flowing waters. 
 
WATER RIGHTS 271 
 
 While there is great uncertainty in these matters, and caution 
 must be used, yet this uncertainty is not such as should deter legiti- 
 mate investment, for it has been shown that good faith in the con- 
 struction of works which are adequate to hold and distribute the 
 water supply, followed by continuous beneficial application has 
 usually been sufficient to constitute an appropriation which will be 
 sustained in legal controversies. In the majority of the cases where 
 water is available and men have proceeded in good faith to utilize 
 it, and have done so, the probability is that they may continue in this 
 without molestation. 
 
 Theory Upon Which Granted. — As stated in previous para- 
 graphs, the theory upon which the right to the use of water is 
 granted by the state or confirmed by the courts is that of beneficial 
 use in the order of priority of appropriation, or of time in which 
 this has been put to such beneficial use. The man who first builds 
 a canal from a stream and utilizes it is almost invariably pro- 
 tected in such use and to the extent to which he has beneficially 
 applied it, as against all subsequent appropriators, especially if he 
 has endeavored to make record of this fact in the proper place with 
 the county or state authorities. 
 
 On nearly every stream notices have been posted at various 
 points claiming a thousand miner's inches or any other large quan- 
 tity. The amount claimed is usually some figure or phrase which 
 appeals to the fancy of the would-be appropriator rather than 
 applicable to the physical facts. Relatively few of these early 
 claimants had any conception as to what was the volume of a miner's 
 inch or of a cubic-foot per second, hence their filings have been 
 for a volume sometimes exceeding that of the stream, or even by 
 mistake for an amount so small as to be insignificant. Adding 
 these claims, the total is sometimes ten times that of the flood flow. 
 In attempting to apply these claims, however, the basis of recogni- 
 tion of appropriation has been not as to the quantity which has 
 been claimed but upon the amount which has been or is actually 
 being used, as shown by the size of the canal and the number of 
 acres irrigated. 
 
 For example, the early appropriator in his ignorance of quantities 
 of waters may have filed upon 10,000 miner's inches, or 200 second- 
 feet. His canal as first constructed may have carried 10 second- 
 feet and may have been enlarged to 20 second-feet. If he has shown 
 due diligence in this enlargement it is probable that when the matter 
 comes to final determination, he may be given a priority of 20 
 
272 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 second-feet, dating from his original notice, or he may be awarded 
 lo second-feet, as a first priority, and an additional lo second-feet 
 to cover the enlargement, this later amount being subsequent to 
 the claims of some other appropriator. If there are, say, loo such 
 appropriators along a stream, and each has made enlargements 
 at different times, it is easy to see how complicated the ofiScial 
 adjudication of water must be where the fact must be established 
 as to the relative dates at which each important enlargement of 
 the various canals has been made. 
 
 Beneficial Use of Water. — ^The principal fact to be established 
 beyond the date of original appropriation and construction is the 
 fact that the water has been put to beneficial use. The mere state- 
 ment that the original claim was initiated at a given time has rela- 
 tively little force as any one may have claimed the waters of an 
 entire river by simply posting notices to this effect. The vital test 
 must be as to whether the claimant actually took the water from 
 the stream and used it beneficially, not wasting it nor trying to hold 
 it for speculative purposes. 
 
 Unless the test of beneficial use is applied, it is easy to create a 
 monopoly of this great necessity of life. A man might lay claim 
 to the waters of many streams and in this way, although owning 
 little, if any, land, be able to levy tribute upon every industry and 
 even upon life itself within the district. Such condition is repugnant 
 to public welfare and hence there has arisen naturally the simple 
 rule that each claimant must prove beneficial use and, having made 
 proof, he should be protected in the continued use until abandon- 
 ment of it has been shown. 
 
 Beneficial use of water for irrigation may be defined as such 
 application of the water as will result in prolongation of life, animal 
 or vegetal, and in the increased value of crops or in the production 
 of power necessary in various industries. While any general 
 definition is necessarily vague, yet in each specific case it is usually 
 easy to determine whether the water has been put to beneficial 
 use by an examination of the facts. It is peculiarly the duty of 
 the engineer in connection with those of the lawyer, in considering 
 the relative rights to water, to make the measurements and deduc- 
 tions which establish the actual facts. For example, a canal con- 
 structed to carry loo second-feet and taking water to i,ooo 
 acres cannot be considered to have a proper claim to its entire 
 capacity for beneficial use, as this amount of water should be suffi- 
 cient for 10,000 acres. 
 
WATER RIGHTS 273 
 
 On the other hand, a canal of lo second-feet capacity which is 
 claimed to irrigate 10,000 acres cannot form the basis for a claim to 
 suflScient water for this 10,000 acres because it is obvious that the 
 water could not be delivered through such a canal, its capacity being 
 entirely too small. Thus, the determination of beneficial use in any 
 particular case or groups of cases is one of fact which can be deter- 
 mined only upon the ground and established by the testimony of 
 competent men. 
 
 Water Rights Apart from Lands. — Under the theory which is 
 generally accepted as correct throughout the greater part of the arid 
 region, there cannot be nor should there be any such thing as right to 
 flowing water independent of ownership of certain tracts of land. 
 In other words, public policy demands that each water right shall be 
 appurtenant to a certain specific tract of land upon which the water 
 may be put to beneficial use. Unfortunately, however, there has 
 grown up in some of the states and been recognized by the courts a 
 theory that the right to the use of water may be of the nature of per- 
 sonal property transferable from one locality to another, that is to say 
 a man may own in a certain stream enough water to irrigate 100 acres. 
 He may rent this to a neighbor one year and take it away and rent it 
 to another for the next year. The objection to this is that such 
 ownership is not consistent with the public welfare. It enables 
 the establishment of a landlordism, repugnant to the popular insti- 
 tutions, as it enables one man to absolutely control the source of life 
 for a large district. 
 
 To illustrate this point, may be taken the extreme case where in 
 medieval times certain authorities claimed the exclusive right to the 
 air over certain districts and endeavored to enforce taxes or tribute 
 upon the use of the air! 
 
 The idea of ownership of water apart from the land has grown up 
 through ownership in the shares of stock of a partnership, cooperative 
 agreement, or corporation, which has built a system of irrigation. 
 For example, a half dozen farmers owning certain lands agree among 
 themselves to build a canal to irrigate these lands. They do not have 
 su£B.cient cash capital and must purchase materials or hire additional 
 help, so a capitalist joins with them with the understanding that he 
 shall own a proportional part of the carrying capacity of the canal. 
 Thus, the farmers obtain the waters for their own lands or for a part 
 of them and from year to year rent from their associate who has furn- 
 ished the capital, the use of the additional capacity of the canal. 
 
 This is a proper and legitimate conception as far as the use of the 
 
 18 
 
274 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 canal is concerned, but it is easy to pass from this rental of the use of 
 the canal to the assumption of the ownership of the water which is 
 taken into the canal. A careful distinction should be drawn between 
 these two. It may be possible and proper to recognize that the water 
 in the canal is appurtenant to the tracts upon which it is used. The 
 persons owning this land may be required to pay a tax or license for 
 the transportation of the water by means of the canal to the lands to 
 which the waters are appurtenant. This is far different in outcome to 
 the proposition that the water is owned by the proprietors of the 
 canal which transports it. As before stated, this claim of ownership 
 of the water by the canal owners has been recognized in some states, 
 but the tendency is to acknowledge the right to carriage only and 
 the right to collect dues as by a common carrier but not as a right of 
 ownership of the flowing water apart from the land. 
 
CHAPTER XIX 
 ECONOMIC FEATURES OF IRRIGATION 
 
 Feasibility of Irrigation. — After all of the detailed studies and 
 examinations have been made of the engineering, legal and related 
 features of any proposed enterprise, then it becomes necessary to 
 study the whole project from the broad standpoint of its feasibility. 
 It is assumed as a matter of course that before starting any detailed 
 investigation, its feasibility is known to be more than probable. As 
 a result of careful studies, this question of feasibility must be prac- 
 tically determined before entering upon expensive construction. 
 
 The prime consideration as regards feasibility is based upon the 
 probable financial outcome. In other words, wiU the enterprise pay? 
 This is true not only from the individual or corporate standpoint, 
 but also from that of the state or nation. The financial reward 
 in the two cases may be estimated on a different basis, that is to 
 say, the individual or corporation considers the financial aspect with 
 reference to direct profits to be attained, while the state may con- 
 sider indirect sources of profit that resulting from a prosperous tax- 
 paying citizenship. 
 
 In either instance, the consideration of feasibility can best be 
 reduced to the easily understood expressions of dollars and cents. 
 This is the measuring stick which must ultimately be applied to all 
 proposed enterprises. 
 
 In turn, the question of financial profit rests upon an infinite 
 variety of conditions such as have been touched upon in the preced- 
 ing pages. These may be grouped under the two general headings 
 of, first, physical difficulties, and, second, obstacles of human origin. 
 The first lie directly within the cognizance of the engineer, the second, 
 and the far more important and difficult, lie only partly within his 
 technical skiU, the remainder being largely within the domain of the 
 lawyer or specialist in various lines. 
 
 Fundamental Questions to be Considered. — Of the physical 
 questions to be answered, the first and most important is usually 
 that of water supply. Throughout the arid region as a rule, there 
 is more good land than there is water, and the chief limitations as 
 before stated rest upon facts as to whether sufficient water can be 
 
 275 
 
276 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 had each year to cover a given area of land. This matter being 
 determined, the next in order is as to the extent and character of the 
 land, and its location with reference to the water supply. The 
 quality of the water should also be given thought as in many parts 
 of the west, especially during low water, the streams carry a very 
 large amount of earthy salts in solution, and in times of flood, great 
 quantities of silt, which tends to choke the canals. 
 
 The human obstacles to which reference has been made are those 
 surrounding the control of the water, or protection of the rights to 
 the continued use of the flowing streams, also those growing out of 
 questions of rights of way for structures and of the relation of the 
 management of the canal system to the irrigators upon whose 
 success as farmers depends the ultimate outcome of the investment. 
 
 Value of Land. — The profits to be made from any irrigation 
 development lie not in sale of the water but in the increased value 
 of the lands which are served. This simple fact has frequently been 
 overlooked and as a result many irrigation investments have been 
 financial failures. There has been too much dependence upon the 
 assumed profits to be made out of the sale of water rights or out of 
 the operation of water supply system, but, as a matter of fact, it 
 has been found that the only profits derived are those from the in- 
 creased value of the land. Assuming that the soil is adapted for 
 agriculture, as it is throughout the greater part of the arid region, 
 the lands without water may be considered as having little or no 
 value in their native state, hardly more than the cost of conveyanc- 
 ing. With water they have a large potential value, or will pay a 
 large rate of interest when developed, upon an investment of $ioo 
 to $500 or more per acre. The cost of bringing water to these lands 
 may be assumed to be $40 an acre and the increase in land values 
 may be several times this cost of providing water. 
 
 This gain in value of land from nothing to $100 an acre or more 
 goes not to the builders of the canal system, but to the owners of the 
 land. If these are the same persons, then the investment may be a 
 financial success, but if one set of men build the works and another 
 set own the land, the profits, whatever they may be, almost invariably 
 go to the landowners. The investors in the irrigation works as 
 distinguished from landowners as shown by past history, have al- 
 most without exception lost their investment. It is not necessary 
 at this time to trace out the reasons why this has occurred, but as 
 a historic fact, this may be stated. The men who have put then- 
 money and time into the construction of irrigation works have been 
 
ECONOMIC FEATURES OF IRRIGATION 277 
 
 "involuntary philanthropists" in that they have developed a coun- 
 try and made possible the creation of wealth for others, but have 
 not been able to bring to themselves a fair share of the reward. 
 
 Increase in Value. — ^The moment that an irrigation system is 
 projected, there attaches to the land which may be covered a specu- 
 lative value and the selling price may jump from the government 
 rate of $1.25 per acre up to I5 or $10 per acre, on the assumption 
 of eairly construction of the project. As the works advance, this 
 speculative value becomes more and more inflated, until the time 
 arrives when it becomes necessary for the owners of the land to 
 begin to repay a part of the money invested in the irrigation works. 
 Then there is usually a sharp decline in land prices. This is because 
 of the realization of the fact that payments must be met and also a 
 better appreciation of the pioneer conditions, namely, that a con- 
 siderable amount of labor and money must be invested in subduing 
 the soil to get it into good productive capacity, or tilth. 
 
 In the more northern states where the crop season is limited to the 
 summer months and where two or possibly three cuttings of alfalfa 
 can be had, the lands as they are brought to a condition of tilth 
 steadily increase in selling price. This may go up to $100 to $150 per 
 acre, dependent upon the degree of care shown in levelling the fields 
 for irrigation and in fertilizing the soil to bring it into the best 
 agricultural condition. 
 
 There is a common fallacy in the statement that the soils of the 
 arid region do not require enrichment, but that the irrigation water 
 supplies all needs. This is far from true, for, although the desert 
 soils frequently contain earthy salts of value to plant life they are 
 usually deficient in nitrogen and frequently in phosphates. The 
 nitrogen can be supplied by cultivating alfalfa, clover, or plants of 
 related families, occasionally turning the green plants under by 
 plow, so as to put the organic matter into the soil, but the phosphates, 
 if needed, must be brought in from other areas. 
 
 In the more southern region, with warmer climates, especially 
 where fruits can be grown, or where the number of cuttings of 
 alfalfa may be increased, the land values are correspondingly 
 larger. When the ground has been properly tilled and young 
 orchards set out, the values reach into hundreds of dollars per acre. 
 Much of this value is given by the labor which has been spent upon 
 the farm, but a considerable portion is what may be called the un- 
 earned increment of value, due to the bringing in of the water. 
 
 This increase in land value is several times the first cost of the 
 
278 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 water, because of the fact that the control of the water is practically 
 a monopoly, there being usually not enough water for all of the good 
 lands. The profits to be obtained are thus those which attach to the 
 creation of a monopoly, and these come, as before stated, not to the 
 builders and owners of the canal system, which transports the water, 
 but to the owners of the land to which the water must neces- 
 sarily be appurtenant. The failure to recognize this simple but 
 fundamental fact has led to many failures in financing irrigation 
 enterprises. 
 
 Soil, Climate, and Crops. — In all considerations of reclamation 
 schemes due attention should be given to the character of soil, 
 to the climatic conditions, and to the possibility of producing 
 certain classes of valuable crops. It is true that these matters 
 are of less immediate importance than those of water supply, because 
 of the fact that taking the arid region as a whole, the soil is usually 
 well adapted to agriculture and the climatic conditions are generally 
 favorable to the production of some kind of crop, but because these 
 matters are secondary they should not be overlooked. 
 
 Most of the soils, especially of the desert areas are somewhat 
 sandy, light, and easily tilled. In the lower valleys, however, 
 there are frequently large areas of clay or adobe which require 
 much more careful manipulation for success. Each class of soil 
 presents its peculiar conditions and problems and requires intelli- 
 gently directed efforts. 
 
 Fortunately, there have been established throughout the arid 
 regions experimental stations where careful observations have been 
 and are being made as to the results of different methods of treat- 
 ment and the agricultural colleges are diffusing information as to 
 peculiar conditions to be met. A book, or in fact many volumes, 
 might properly be devoted to the subject of soils in their relation to 
 irrigation, but it is sufficient in the present connection to call atten- 
 tion to this fact, and to the necessity of having an expert examination 
 of the soils which it is proposed to irrigate, in order to determine 
 in a broad way the fundamental questions as to the amount of 
 water which may be needed and especially the probable behavior 
 with respect to necessity for drainage. 
 
 As regards climate in its relation to irrigation, it may be said 
 that irrigation is most beneficial and is absolutely necessary where 
 there are droughts prevailing through a whole or part of the crop 
 season, which is usually the case where the rainfall throughout 
 the year is less than lo to 15 in. in depth. A small amount of 
 
ECONOMIC FEATURES OF IRRIGATION 279 
 
 rainfall means as a rule a large amount of sunshine. As the sun 
 is the source of all life and growth, it follows that with an artificial 
 supply of moisture in these regions where the sun shines nearly 
 every day, the plant growth must be rapid, even though during 
 much of the year the climate is notably cold. It is a matter of 
 surprise to note how successful irrigation is, for example, in portions 
 of Canada where, taking the year through, there is a very cold 
 climate. The summer season though short is notable for its long 
 hot days. Where water can be applied, the plant development 
 during this short summer is extremely vigorous, thus it results 
 that irrigation is being extended into the Canadian northwest; 
 to a country which is popularly supposed to have an almost artic 
 climate but which actually produces notably large crops during 
 the short, intense, summer period. 
 
 The largest success under irrigation is attained, of course, in 
 the truly desert areas of the southwest, where the climate is such 
 that plant growth continues throughout the winter season with 
 a very short period, if any, of rest. Here crop follows crop in rapid 
 succession; alfalfa, for example, can be cut at intervals of five or 
 six weeks, and field crops may be had in rapid rotation, sometimes 
 three cultivations on the same ground being successful during each 
 calendar year. 
 
 With respect to the crops which may be raised, this is a matter 
 which must be governed not only by the character of the soil but 
 very largely by human conditions, namely, those of transportation 
 and market. In attempting to develop any new area, it is to be 
 assumed that transportation has not yet been fully provided, and 
 the question to be given serious consideration is as to the probability 
 of early construction or improvement of railroads, and other means 
 of taking the crops directly to the centers of population. 
 
 In some localities there may be in existence a local demand for 
 crops such as that at mining camps in the mountains. In others, 
 there may be need of forage for winter feed and for cattle upon the 
 open range. For most localities crops should be selected in accord- 
 ance with the means of getting these to the cities and towns and of 
 selling them in competition with similar products from other pro- 
 ducing areas. 
 
 It is a common mistake, especially in pioneer communities, to 
 attempt the raising of varieties of crops which have been successful 
 elsewhere, but which are not adapted to the peculiar conditions. 
 The farmers coming from other localities naturally try to utilize the 
 
280 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 results of former experience, and do not realize that this experience 
 is inapplicable to the new home. 
 
 Many farmers, for example, have been successfid in raising grain 
 by the ordinary or dry-farming methods and do not appreciate that 
 the cost of irrigation does not justify continuing in this line. They 
 do not keep sufficiently accurate accounts to know where their losses 
 are occurring, and may keep on year after year planting those crops 
 which are not netting them a sufficient amount to be remunerative. 
 It is this failure to appreciate the relative cost and values of various 
 crops which has led to the lack of success and relatively low crop 
 values throughout a considerable part of the arid regions. 
 
 Permanence of Water Supply. — All values rest upon the water 
 supply. The permanence of this supply, as previously noted, must 
 be looked into not merely from the physical side, but even more 
 carefully from the legal, in order to have proper assurance that if 
 water is found to be in existence the right to the use of it may be 
 perpetually maintained. The permanence from the physical stand- 
 point is a matter which may be inferred only from an examination of 
 records of the past. The assumption is made that whatever has 
 occurred in the past wiU probably occur again in the future. It is 
 necessary, therefore, to obtain every possible fact concerning the 
 behavior of the stream from which water is to be obtained and of 
 similar streams having like conditions. If, for example, it has been 
 found through observations carried on during ten years, that the 
 average flow during the summer is i.ooo cu. ft. per second, it is 
 assumed that this average will be maintained for another ten years. 
 
 If there has been a large flood upon this or upon a similar stream, 
 provision must be made for passing such flood and even a larger one 
 around the works. On the other hand, if a drought has occurred 
 allowance must be made for a similar drought with the possibilities 
 that it may be somewhat more severe. 
 
 Provision must be made for all of these conditions based upon 
 the fundamental conception that nature repeats itself. Our 
 knowledge is, of course, confined wholly to what has happened in 
 the past; we make all plans and investments upon the assumption 
 of the permanency of natural phenomena. It may be that the 
 period during which observations have been made is abnormal, that 
 is to say, that for the ten years of observation, there may be more 
 or less available water than has occurred in previous decades of which 
 we have no exact records. This is the chance which must be taken, 
 but experience has shown that by allowing a reasonable margin 
 
ECONOMIC FEATURES OF IRRIGATION 281 
 
 for safety, works may be planned and built upon these as- 
 sumptions. 
 
 Cost of Constructing Works. — The cost of constructing works is 
 the next topic in order after considering the questions of feasibility as 
 regards water supply, soil, climate, and crops. It has come to be an 
 axiom that this cost is generally greater than the original estimate. 
 This is due not so much to lack of care and thoroughness in prepar- 
 ing estimates as to the fact that the work is pioneer in its character, 
 and improvements are suggested or new needs arise so rapidly that 
 works which were planned in one year as adequate for the purpose 
 in mind are found to be unsuited or undesirable by the time construc- 
 tion is well advanced. Many changes must be made, or additional 
 details provided which were not known or not considered necessary 
 in the original scheme. It is, of course, possible that an engineer 
 may plan works and build them exactly as planned and within the 
 original estimates, but this condition is one which with existing irri- 
 gation systems does not take place under ordinary circumstances. 
 
 The engineer may plan for certain works to meet the then pre- 
 vailing conceptions, but the owners or financiers usually conclude 
 that it is necessary to add certain extensions or modify details such, 
 for example, as increasing the size of the reservoir, or of the main 
 canal, or adding a pumping plant. Thus, as a result the works 
 cost more than anticipated, and, comparing the original statements 
 of cost with the actual expenditures made it is seen that the latter 
 are far in excess of the estimates, but the reasons for this are rarely 
 given. 
 
 Men's ideas with reference to limits of practicability or cost of the 
 works have rapidly expanded. The small canals built before 1900 
 were cheaply executed, the structures were of wood and of tempo- 
 rary character. The location was made with reference to keeping 
 the construction cost to the minimum and much of the work was 
 done by the farmers themselves, no account being taken of what is 
 generally termed the overhead cost including that of planning and 
 organization of the work. 
 
 At the same time, the estimates of the area watered were very 
 liberally made. If some water was provided for a farm, it was 
 habitually stated that the entire area say of 160 acres was under 
 irrigation, even though water had only been as a matter of fact 
 applied to a portion of it. The capacity of the canal might not be 
 enough to supply all of the lands which were claimed to be irrigated. 
 For these reasons the cost per acre of irrigation was stated at an 
 
282 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 extremely low price, less than $15 per acre. Beginning abofut the 
 year 1900, a cost of $20 per acre for irrigation was considered high, 
 but when it began to be appreciated that the 'and with a sure water 
 supply would yield a large return on a value of $50 or even $100 
 per acre, it was recognized that larger investments in construction 
 would be justified. Year by year the limits of assumed feasibility 
 have been increased, so that by 1905, it was assumed that $30 per 
 acre was large, then $40 per acre, and finally by 1910, a cost of rec- 
 lamation of $60 per acre was not considered prohibitory, for lands 
 especially in the southern part of the country. In fact, when con- 
 sideration is had of the great value of orchard lands an expenditure 
 of $100 or more per acre to provide water is feasible. In semi- 
 tropical lands, for example, in the Hawaiian Island, where pumping 
 plants have been erected for raising water for irrigation to a height 
 of 550 ft., an outlay of several hundred doUars per acre is not con- 
 sidered out of the ordinary. 
 
 In the northern temperate regions, for example, in Colorado and 
 Montana, for the ordinary field crops an investment of $40 to $60 
 per acre may be now considered as large but not prohibitory. This 
 may be increased notably for warmer regions with longer crop 
 season, such as those of southern Idaho, and portions of Oregon and 
 Washington. Going south from here to points as in Arizona and Cali- 
 fornia, where crops grow throughout the greater part of the year, an 
 increase of 50 per cent, in the amount above named may be con- 
 sidered as moderate. 
 
 If estimates are based on the crop production of thoroughly ir- 
 rigated lands it can readily be seen that these give a good income on 
 an investment of from $200 to $500 per acre, so that theoretically, 
 the figures above given could be increased several fold, but as a 
 matter of fact, under existing conditions, it is hardly safe to figure 
 on this basis, although it is possible to look forward to a time when 
 far larger investments than now considered wise will be the rule rather 
 than the exception. 
 
 Other Costs. — It must not be assumed that the cost of an irriga- 
 tion system is simply that of the engineering or construction. There 
 are other costs which may equal or exceed these and neglect of 
 which in the preliminary estimates frequently leads to financial 
 ruin. These are the somewhat vague and intangible expenses 
 of the organization, the so-called overhead charges, especially of 
 commission and interest upon bonds, or upon other securities 
 issued for construction purposes. It is not infrequently the case 
 
ECONOMIC FEATURES OF IRRIGATION 283 
 
 that after the engineer has carefully estimated all of the construction 
 cost and has allowed 15 per cent, or 20 per cent, for contingencies, 
 the business man must double this to cover the items above noted. 
 
 Taking the ordinary conditions of private irrigation systems 
 it may be said that assuming the engineer's estimate of construction 
 at 100 per cent., the other items to be added will be about as follows : 
 
 Preliminary examinations, organization and promotion, 10 per 
 cent. 
 
 General administrative, 10 per cent. This is after the funds 
 have been raised, the general plans determined upon and construction 
 carried to completion. 
 
 Interest on bond issue, 20 to 30 per cent. This is assumed to 
 cover most of the construction cost, and is estimated at 6 per cent, 
 per annum on the period required in the construction of large 
 systems. 
 
 We thus have from 40 to 50 per cent, of the construction cost 
 to be added at the time when the works are completed. 
 
 Beginning with the time of completion of the works and the 
 beginning of active irrigation from then on is the period of greatest 
 diflSculty and stress. Settlement of the lands is usually slow, the 
 farmers must experiment, the markets are to be established, and 
 five, ten or more years may elapse before the land is completely 
 irrigated and the farmers are able to make notable payments. 
 During this time the cost of operation and maintenance has been 
 large and this with the interest on bonds or other securities may 
 amount to 75 per cent, or even 100 percent, of the actual construc- 
 tion cost. 
 
 Markets and Transportation Facilities. — Ks before stated, the 
 question of markets and of transportation facilities must be con- 
 sidered in any irrigation scheme. These are not usually at hand 
 when the project is under consideration, but come as a natural out- 
 growth of the development of irrigation. As soon as it is apparent 
 that products of the soil are to be handled in quantity, there is 
 aroused an interest in the matter on the part of transportation 
 agencies and markets are created in accordance with the products 
 available. It is necessary, therefore, to place large reliance upon 
 these future developments. 
 
 Any considerable area of desert land, say 50,000 acres more or 
 less to be brought under cultivation, will attract railroad builders 
 and one or more railroads will naturally be built into the territory 
 as soon as the success of the works is assured. There is, of course. 
 
284 PRINCIPLES OF IRRIGATION ENGINEERING 
 
 an element of uncertainty in this matter, but it is suflScient to call 
 attention to the fact that it is not possible in advance of construction 
 to be sure of railroads and markets and a certain anioimt of chance 
 may properly be assumed, and in fact is always assumed, in the 
 building of these works of reclamation. 
 
 The success of the farmer and his consequent ability to repay the 
 building cost of the works and the expense of operation and main- 
 tenance, are, of course, dependent upon his ability to dispose of the 
 crops. On the other- hand, there is a certain amount of elasticity 
 in that the crops can be varied from year to year to suit the changing 
 conditions. If, for example, at first there are no railroad facilities, 
 he can raise forage crops which are, as a rule, eagerly sought by the 
 stockmen, and if prices are sufficiently low, cattle and sheep will be 
 driven into the region for winter feeding or fattening. As trans- 
 portation facilities improve, crops can be produced which may be 
 shipped and higher and higher grades of perishable fruits can be 
 produced. 
 
 Security of Investment. — ^AU of these considerations of feasibility 
 or practicability lead up to the point vital to the investor, namely, 
 as to whether the money spent in the construction of irrigation works 
 will be returned within reasonable time, with reasonable profit, and 
 reasonable interest. In general, it may be said that investments in 
 irrigation works properly planned with reference to adequate water 
 supply and climatic and other conditions should be safe and prof- 
 itable. Assuming that care and intelligence have been displayed in 
 guarding the rights to the water, in planning and building the works, 
 and in adapting them to the peculiar conditions, there is nothing 
 which should be on a similar financial basis, because of the large 
 annual profits which may be derived by the farmers from intelli- 
 gently tilling the soil. 
 
 Under the above assumptions, the security and the value of the 
 works to the community is beyond question, as they are vital not 
 merely to production of crops but to the maintenance of population 
 and even to the sustenance of life itself. As to whether they will be 
 profitable or not, this is another matter. It has already been stated 
 that the speculative profits or those growing out of the increase in 
 Values comes to the owner of the lands rather than to the builders 
 or owners of the water-supply system as distinguished from the 
 landowners. The fact that most irrigation projects as such have 
 not been financially successful, does not reflect upon the value of 
 the investment, but rather upon the lack of experience, skill and 
 
ECONOMIC FEATURES OF IRRIGATION 285 
 
 good judgment in planning and building and operating the works. 
 To illustrate the point in mind, the irrigation works may be com- 
 pared to the foundations of a building. Upon them rests the whole 
 social and economical superstructure. Their value and importance 
 is beyond doubt, but like the foundations of a building they may 
 return very little, if any, direct profits on the investment. These 
 come from the superstructure itself, which is carried by the founda- 
 tions. Of course, if they are poorly designed and imperfectly exe- 
 cuted, everything built upon them is correspondingly weakened. 
 
 Summing up the entire consideration of economic features, it 
 may be said that we are still in what may be termed the pioneer 
 stage of development, particularly in the solution of the great 
 problem of the proper relation of all these matters one to the other. 
 
 In each one of the separate details large experience has been had 
 and it is possible to find a man skilled in engineering or in economics 
 who can successfully handle each one of these questions or even 
 several of them, but when it comes to the entire combination, few 
 men, if any, have had the experience in all the parts needed to pro- 
 duce success. In other words, each separate part may be properly 
 designed and operated but the whole assemblage may be a failure. 
 
 In this respect the situation is very similar to that in the organi- 
 zation of a large manufacturing establishment which has been 
 initiated by men who have not been brought up in this particular 
 line of business. It may be assumed that each one of a group of 
 several experts is competent in his specialty; for example, one man 
 in designing and installing the machinery, another man in the 
 purchasing of raw material, another in selling, etc., but these men 
 have never before been associated together and have not grown 
 up with this particular combination. Thus, we have the condition 
 where each part may be excellent in itself but the lack of coopera- 
 tion or of so-called "team-play" prevents the success of the whole, 
 although this lack of success is not attributable to the defect in any 
 one operation. It is this condition which prevails on many of the 
 large irrigation projects in that the whole assemblage of parts and 
 their successful operation is still largely in the experimental stages. 
 
 Ultimate Results. — The engineer may derive satisfaction from his 
 work Ln irrigation not only from the financial returns but from the 
 consideration of the fact that these works have the largest direct bear- 
 ing upon the material prosperity not only of individuals and commu- 
 nities, but of the state and nation. They form the foundations 
 upon which are built agricultural communities, villages, lines of 
 
286 PRINCIPLES QF IRRIGATION ENGINEERING 
 
 railroad, and the whole social fabric, embracing not only the 
 farnaers, but all of the trades and occupations which have to do 
 with transporting or manufacturing the materials produced by the 
 farmer, or designed for his needs. 
 
 The engineering works thus not only directly make opportunities 
 for homes for the men who till the soil, but for every home thus 
 created there is possibility of another home for the mechanic or 
 artisan or railroad man who is engaged in supplying the needs of 
 the farmer or in transporting the raw and manufactured products 
 from or to the farm. To the investor also there is offered oppor- 
 tunity for not merely increasing his capital, if intelligently used, 
 but of obtaining this increase through assisting other men to utilize 
 the natural resources which otherwise go to waste. Finally, to the 
 public man or statesman, there is no subject more fascinating or more 
 important than that of watching and aiding in the development of 
 the country through the intelligent conservation and use of these 
 natural resources. 
 
INDEX 
 
 Acquiring water rights, 268 
 Acre-foot, definition, 27 
 Advantages derived from irrigation, 6 
 Alignment of canals, 38 
 AUiali, effect on soil, 138 
 Amount of water required for irriga- 
 tion, 34, 158 
 Applying water to the land, methods 
 
 of.S 
 Arid regions of the U. S , 8 
 
 topographic features of, 10 
 
 soil of, 10 
 
 regions of the world, 3 
 Aridity, causes of, 8 
 Arkansas river underflow, 119 
 Arrowrock dam, Boise River, Idaho, 
 
 250 
 Automatic gages, 160 
 
 Banks, care of, 164 
 
 erosion of, 41 
 
 material for, 43 
 
 roadways on, 56 
 
 slopes and widths of, 41 
 Belle Fourche project dam, 225, 245 
 Bench flumes, 83 
 
 Beneficial use of water, definition, 272 
 Benefits derived from irrigation, 4 
 Berm, definition and advantages, 41 
 Bermuda grass for protecting banks, 
 
 165 
 Bigelow, Prof. Frank, table of evapora- 
 tion losses, 17s 
 Boring and test pits for dam sites, 192 
 
 for drainage information, 147 
 Bridges, 96 
 Brush and log dams, 204 
 
 Canal and ditch, definition, 5 
 banks, care of, 164 
 
 slopes and width, 41 
 capacity, 35 
 
 determining, 36 
 channels, sitting of, 46 
 cross-section of, 38 
 embankments, 39-43 
 lining, 55 
 driers, 167 
 structures, classification, 61 
 
 protection of, roo 
 systems, definition, 102 
 
 Canals, alignment of, 38 
 
 and laterals, 102 
 
 cleaning, 165 
 
 economic construction of, 37 
 
 excavation, 47 
 
 grades and velocity of, 44 
 
 lateral draining of, 57 
 
 lined, 55 
 
 location, 36 
 
 measuring devices for, 97-99 
 
 moss in, 165 
 
 narrow versus wide, 39 
 
 operating and controlling de- 
 vices, 65 
 
 priming, r64 
 
 protection against seepage, 52-55 
 
 right-of-way for, 59 
 Capacities, computation of for reser- 
 voir sites, 188 
 Capacity of canals, 35 
 
 determining, 36 
 
 of culverts, 81 
 
 of drains, 147 
 
 of laterals, 105 
 
 of outlets, 248 
 
 of spillways, 197, 259 
 
 of turnouts, 70 
 Care of banks, r64 
 Cement tiling drains, 144 
 Centrifugal pumps, 120 
 Character of water supply, 15 
 Check system of applying water, 6 
 Checks and drops, 71-78 
 Cippoletti weirs, in 
 Classification of canal structures, 61 
 Classifying excavation, 49 
 Cleaning canals, 165 
 Clear Lake, Ore., dam, 226 
 Climate, soil and creeps, 278 
 Climatic, conditions, 14 
 Closed drains, 144 
 Cold Springs, Ore., dam, 225 
 Compacting earth dams, 218 
 Compressed-air pumping plant, 127 
 Conconully dam, Okanogan project, 
 
 218, 251 
 Concrete dams, 238 
 
 drops, 74 
 
 core walls in earth dams, 220 
 
 flumes, 86 
 Constancy necessarj' in water supply, 18 
 
 287 
 
288 
 
 INDEX 
 
 Construction of bridges, 96 
 
 of canals, 37 
 
 of checks and drops, 71-78 
 
 of culverts, 80-83 
 
 of dams, 194-197 
 
 of earth dams, 214 
 
 of fish ways, 257 
 
 of flumes, 83-89 
 
 of headgates, 62 
 
 of masonry dams, 232 
 
 of outlet works, 248-262 
 
 of rock-fill dams, 227 
 
 of siphons, 92-95 
 
 of sluice gates, 79 
 
 of spillways, 79, 196, 258, 259-261 
 
 of tunnels, 81-92 
 
 of turnouts, 67 
 
 of water cushions, 75 
 Continuous flow system of water dis- 
 tribution, 153 
 Contour maps, 105 
 
 for reservoir sites, 187 
 Controlling apparatus, 65 
 Core walls in earth dams, 219 
 Cost of canal riders, 167 
 
 of constructing irrigation works, 
 281 
 
 of excavating, 49 
 
 of hydroelectric pumping plants, 
 
 131 
 
 of irrigation by windmills, 123 
 
 of pumping, 132 
 
 of operation, 167 
 
 of reservoirs, 184 
 
 of storage, 183 
 
 of test pits and borings for dam 
 sites, 193 
 Crib and pile dams, 207 
 
 dams, 205 
 Crop values increased by irrigation, 6 
 Crops, soil and climate, 278 
 Cross-section of canals, 38 
 
 of laterals, 108 
 
 of masonry dam, 235 
 Cross-sectional area of culverts, 8 1 
 
 area of streams, determining, 31 
 Croton watershed. New York City, 
 
 dam, 245 
 Crushing strength of stone, 241 
 Culverts, 80-83 
 Curved masonry dams, 239 
 Curves in canal construction, 38 
 Cut-off trenches for earth dams, 222 
 
 walls, 67 
 Cycles of precipitation, 20 
 
 Dam construction, 194-197 
 Dam foundations, 191 
 
 selection of proper type of, 199 
 
 site, surveys of, 190 
 
 Dam sites, borings and test pits, 192 
 Dams, crib, 205 
 earth, 211-225 
 
 construction of, 214 
 core wall, 219 
 cut-off trenches, 222 
 drainage, 224 
 dikes, 224 
 examples, 225 
 foundation, 211 
 Umit of height, 225 
 materials for, 212 
 placing materials, 214 
 protection of slopes, 223 
 puddle core, 221 
 section of, 213 
 seepage under, 213 
 site for, 211 
 water-tight face, 221 
 elementary forms of, 200 
 framed, 208 
 internal stresses, 240 
 kinds of, 200 
 log and brush, 204 
 masonry, 232-247 
 concrete, 238 
 curved, 239 
 foimdations, 235 
 heights, 245 
 multiple arch, 239 
 overflows, 242 
 protection of toe from erosion, 
 
 244 
 rubble concrete, 223 
 safe foundation limits, 214 
 section, 235 
 typical, 24s 
 principal storage and diversion 
 
 table of, 247 
 rock-fill, 226-231 
 
 advantages over earth dams, 2 2 7 
 foundation, 228 
 materials, 228 
 section and slopes, 229 
 seepage, 231 
 site, 227 
 
 water-tighting, 230 
 timber, 200-210 
 
 conditions of stability, 203 
 Umits of height of, 209 
 types of, 204 
 use of, 202 
 water-tightntss, 204 
 when applicable, 202 
 Dthvtry boxes, no 
 
 points of water, 109 
 Depth of drains, 148 
 Desert Land Act, provisions of, 265 
 Design of spillways, 259 
 Determination of storage required, 179 
 of storage supply, 171 
 
INDEX 
 
 289 
 
 Dikes, 224 
 
 Discharge of streams, computing, 31 
 Distance between drains, 149 
 Distributaries, flume and pipe, 113 
 Distribution of water, 152 
 
 continuous flow system, 153 
 
 periodic rotation system, 154 
 
 systems, 103 
 Ditch and canal, definition, s 
 Drainage, benefits of, 138 
 
 classification, 136 
 
 effects of, on soil, 142 
 
 investigation, 146 
 
 lateral, of canals, 57 
 
 need for, 136 
 
 of earth dams, 224 
 Drains, capacity of, 147 
 
 depth of, 148 
 
 distance between, 148 
 
 grades and velocity of flow, 150 
 
 open and closed, 143 
 
 relief and intercepting, 145 
 Drops and checks, 71, 78 
 
 notched, 77 
 
 vertical and inclined, 71 
 Droughts and floods, 32 
 Duty of water, definition, 157 
 
 Early methods of irrigation, 3 
 Earth dams, 211—225 
 
 construction of, 214 
 
 core wall, 219 
 
 cut-off trenches, 222 
 
 drainage, 224 
 
 dikes, 224 
 
 examples of, 225 
 
 foundation, 211 
 
 Umit of height, 225 
 
 materials for, 212 
 
 placing materials, 214 
 
 protection of slopes, 223 
 
 puddle core, 221 
 
 section of, 213 
 
 seepage under, 213 
 
 site for, 211 
 
 water-tight face, 222 
 East Park dam, 237 
 Economic questions in storage, 181 
 Elementary forms of dams, 200 
 Embankments, 39, 43 
 
 consolidating, 49 
 Equivalents in hydraulic computation, 
 
 29 
 Erosion at flume ends, 88 
 
 of canal banks, 31 
 
 protection of dam toe from, 244 
 of spillways against, 261 
 Estimating cost of excavating, 49 
 Evaporation losses, 106 
 
 loss in storage, 175 
 Evaporation's effect on runoff, 23 
 19 
 
 Excavating, estimating cost of, 49 
 
 machinery, 48 
 Excavation, classifying, 49 
 
 of canals, 47 
 
 specifications for, 50 
 Experience valuable in irrigation, 7 
 
 Facing earth dams, 221 
 
 rock-fiU dams, 230 
 Farming, intensive, 13 
 Feasibility of irrigation, 275 
 Fishways, 256 
 Flash boards, 65 
 Flood water, value of storing, 18 
 Flooding system of applying water, s 
 Floods and droughts, 32 
 Flow in drains, velocity, 150 
 Flume distributaries, 113 
 Flumes, 83, 88 
 
 and trestles, 58 
 
 rating, iii 
 
 velocity and flow of water in, 88 
 Foundation of earth dams, 211 
 
 rock-fill dams, 228 
 Foundations of masonry dams, 23 s 
 
 for dams, 191 
 
 safe hmits for, 241 
 Forest reserves, 10 
 Framed dams, 208 
 
 Freezing, effect of on canal lining, 55 
 Frequency of irrigation, 156 
 Fresno scrapers, 48 
 Furrow system of applying water, 6 
 
 Gaging station, 31 
 Gasolene and oil plants, 124 
 Gate towers, 250 
 Gates, valves, 256 
 
 character of, 255 
 
 operation of, 252 
 
 outlet, location of, 250 
 
 vibration of, 253 
 Gila river, discharge of, 16, 17 
 Grades and velocity of canals, 44 
 
 of drains, 150 
 Granite Reef, Ariz. , dam, 242 
 Green river, discharge of, 16, 17 
 Ground water, definition, 140 
 
 Headgates, 62 
 
 Height, limit of, of timber dams, 209 
 maximum, for pumping for irriga- 
 tion, 13s 
 Human element in irrigation work, 162 
 Huntlfcy water power pumping plant, 
 
 125 
 Hydraulic computations, list of equiv- 
 alents, 29 
 rams, 125 
 sluicing, 216 
 Hydroelectrical power, 127 
 
290 
 
 INDEX 
 
 Hydroelectric power, computing, 129 
 Hydrographic conditions limiting stor- 
 age, 172 
 
 Intensive farming, 13 
 
 Intercepting drains, 14s 
 
 Internal stresses upon masonry dams, 
 240 
 
 Irrigation, amoimt of water required 
 for, 34 
 benefits derived from, 4 
 by windmills, 123 
 definition, i 
 feasibility of, 275 
 frequency of, 156 
 head, definition, 107 
 history and development, i 
 increases land values, 277 
 in the U. S., first development, 3 
 season, length of, 155 
 system, maintenance, 163 
 systems, human element in, 162 
 versus non-irrigation, 6 
 
 Kennedy, R. C. , on silting of canals, 46 
 
 Land and water ownership, 273 
 Land values, 276 
 
 Lands, arid, preparation of for irri- 
 gation, 12 
 Laguna Dam, 67, 195 
 Lateral drainage of canals, 57 
 
 systems, surveys for, 104 
 Laterals, 102 
 
 accessibility to, 114 
 
 capacity of, 105 
 
 cross-section of, 108 
 
 location of, 107 
 Laws, of early times regulating water 
 
 supply, 2 
 Length of irrigation season, r55 
 Lined canals, 55 
 Lining for tunnels, 91 
 Locating an irrigation project, 13 
 Location and type of spillways, 260 
 
 of canals, 36 
 
 of laterals, 107 
 
 of outlets, 248 
 Log and brush dams, 204 
 Loss by seepage, 173 
 
 Machinery for excavating, 48 
 Maintenance, cost of, 167 
 
 of irrigation systems, 163-169 
 Maps for dam site, 191 
 
 of reservoir sites, 186 
 Markets and transportation facilities, 
 
 283 
 Masonry dams, 232-247 
 
 rubble concrete, 233 
 
 foundations, 235 
 
 Masonry, section, 235 
 
 concrete, 238 
 
 curved, 239 
 
 multiple arch, 239 
 
 internal stress, 240 
 
 safe foimdation Umits, 241 
 
 overflows, 242 
 
 protection of toe from erosion, 244 
 
 heights, 24s 
 
 typical, 245 
 Material for canal banks, 43 
 
 for flume construction, 86 
 Materials for dams, 194 
 
 for earth dams, selection, 212 
 placing, 214 
 
 for rock-fill dams, 228 
 Measurement of water, methods, 30 
 supply, 26 
 used, 160 
 Measuring devices, 97, in, 161 
 
 miner's inches, 28 
 
 streams, 31-32 
 
 water, methods of, 27 
 Mechanical meters, 99 
 Metal flumes, 86 
 Meters, 99 
 Methods, 4 
 
 of acquiring water rights, 269 
 Miner's inch definition, 28 
 
 of application, 5 
 Minidoka project, loss by seepage, etc., 
 
 160 
 Mining and irrigation interdependent, 
 
 13 
 Moss destruction in canals, 165 
 Multiple arch masonry dams, 239 
 
 Newlands Reclamation Act, 266 
 North Platte project, loss by seepage, 
 
 etc., 160 
 North Platte River dam, 246 
 
 Oil and gasolene plants, 124 
 Okanogan project dam, 218 
 Open drainage ditches, 150 
 Operation, cost of, 167 
 
 of irrigation works, 152-169 
 Operating and controlling device, 65 
 Organic vegetable matter lacking in 
 
 arid soil, 12 
 Orifice, submerged, 112 
 Orland project, Calif., dam, 237 
 Organization for operation of irriga- 
 tion system, 166 
 Outlet gates, location of, 250 
 
 operation of, 252 
 
 vibration of, 253 
 
 character of, 255 
 Outlets, 248-262 
 
 capacity, 248 
 
 location, 248 
 
INDEX 
 
 291 
 
 Outlets, of gates, 250 
 
 gate towers, 250 
 
 operation of gates, 252 
 
 erosion, 252 
 
 vibration of gates, 253 
 
 character of gates, 254 
 
 fishways, 256 
 
 spillways, 258-262 
 Overflow masonry dams, 242 
 
 spillways, 79 
 Ownership of water apart from the 
 
 land, 273 
 Owl Creek, S. D., dam, 225 
 
 Pathfinder, Wyo. , dam, 246 
 Permanence of water supply, 280 
 Permanent canal structures, 61 
 PermeabiUty of canal banks, 43 
 Periodic droughts, 32 
 
 rotation system of water distri- 
 bution, 154 
 Piling core walls, 220 
 Pipe distributaries, 113 
 Points of delivery of water, 109 
 Possibilities derived from irrigation, 6 
 Power for pumping, 121 
 Precipitation, cycles of, 20 
 
 at Salt Lake City, 20 
 Preparing land for irrigation, 1 2 
 Priming canals, 164 
 Priority rights protected, 271 
 Protection of canal structures, 100 
 
 of priority claimants, 271 
 Puddle core walls, 221 
 Pumping, cost of, 132 
 
 feasibility of, 134 
 
 for irrigation, maximum lift, 135 
 
 plants, 116-13S 
 
 plant at Huntley Montana, 126 
 at Minidoka Project, Idaho, 130 
 
 power for, 121 
 
 steam power for, 123 
 
 systems, water supply for, 117-119 
 Pumps, character of, 120 
 
 Quality of water supply, 33 
 
 Ramming earth dams, 219 
 
 Rainfall and runoff, ratio between, 21 
 
 divergence in, 19 
 Rate of flow, definition, 27 
 Rating flumes, in 
 
 Ratio between rainfall and runoff, 21 
 Recording systems, 167 
 Records of stream flows, 198 
 Relief drains, 145 
 Reservoir losses, 174 
 
 site, choice of, 188 
 
 sites, surveys, 186 
 
 computation of capacities, 188 
 Reservoirs, requirements for sites, 185 
 
 Reservoires, shallow versus deep, 189 
 
 table of costs of, 184 
 Ridges, 103 
 Right-of-way, 115 
 
 for canals, 59 
 Rights to water, method of determina- 
 tion, 264 
 Riparian rights, 267 
 Rivers, action of waters of, 16 
 
 underflow of, 119 
 Roadways on canal banks, 56 
 Rock-fill dams, 226-231 
 
 advantages over earth dams, 227 
 
 sites, 228 
 
 foundation, 228 
 
 materials, 228 
 
 section and stapes, 229 
 
 water-tighting, 230 
 
 seepage, 231 
 Roosevelt dam, Ariz., 245 
 Rubble concrete dams, 233 
 
 masonry dam, typical, 234 
 Runoff affected by evaporation, 23 
 
 amount possible to be stored, 172 
 
 annual, .170 
 
 comparison of, 26 
 
 definition, 20 
 
 in inches, definition, 29 
 
 influences affecting, 2 1 
 
 on different watersheds, 23 
 
 ratio of, to storage capacity, 177 
 
 Sagebrush for wind shield, 12 
 San Leandro, Calif., dam, 225 
 Salt Lake City, annual precipitation 
 at, 19, 20 
 Valley, first irrigation in the U. S., 
 
 3 
 Salt River project, Ariz. , dam, 246 
 Screen, 100 
 
 Salts in water supply, 33 
 Second-foot, definition, 28 
 Section of earth dam, 213 
 
 of rock-fill dam, 229 
 Sections and slopes of some principal 
 
 canals, 47 
 Security of investment, 284 
 Seepage, guarding against, loi 
 
 loss by, 5,36, 106, 159, 173 
 
 prevention of under earth dams, 
 213 
 
 protection against, 52-55 
 
 through earth dam, 219 
 
 through rock-fill dams, 231 
 Shoshone dam, Wyoming, 197, 246 
 Side-hiU flumes, 84 
 Silt, prevention, 66 
 Silting of channels, 46 
 Siphon foundations, 94 
 
 materials, 95 
 Siphons and inverted siphons, 92-95 
 
292 
 
 INDEX 
 
 Site for earth dams, 211 
 
 Sites adapted to rock-fill dams, 227 
 
 for dams, 190-199 
 
 for reservoirs, 183-188 
 Sluice gates, 66, 79 
 Slopes of earth dams, protecting, 223 
 
 of rock-fill dam, 229 
 
 Soil, effects on, of alkali, 138 
 
 of drainage, 142 
 
 of the arid regions of U. S. , 10 
 
 studying in drainage, 150 
 Source of water supply, 15 
 Specifications for excavation, 50 
 Spillways, 79, 196, 258-262 
 
 requirements, 258 
 
 design, 259 
 
 capacity, 259 
 
 location and t3rpe, 260 
 
 grades and velocity, 261 
 
 erosion, 261 
 Stability of timber dams, 203 
 State control of water, 266 
 Steam power for pumping, 123 
 Stone, crushing strength of, 241 
 Storage capacity, ratio of runoff to, i77 
 
 cost of, 183 
 
 economic questions in, 181 
 
 hydrographic conditions limiting, 
 172 
 
 losses from seepage, 173 
 from evaporation, 175 
 
 of flood water, 18 
 
 required, determination of, 179 
 
 supply, determination of, 170 
 Strawberry River dam, 221 
 
 Valley tunnel, 89 
 Steam flows, records of, 198 
 
 measurement, 32 
 Streams, determining cross-sectional 
 area, velocity and discharge, 
 
 31 
 
 underflow of, 118 
 Sub-irrigation, 6 
 
 Sudbury River, Boston, dam, 245 
 Surface drainage, 136 
 Surveys for distribution systems, 104 
 
 of dam site, 190 
 
 of reservoir sites, 186 
 Susquehanna River, discharge of, 16, 17 
 Systems of applying water, 5, 6 
 
 Tabeaud, CaUf.,dam, 225 
 Table, cost of reservoirs, 184 
 
 monthly evaporation losses, 176 
 mean annual runoff for various 
 
 water-sheds, 24, 25 
 principal storage and diversion 
 
 dams, 247 
 sections and slopes of some 
 principal canals, 47 
 Temporary canal structures, 61 
 
 Test pits and borings for dam sites, 192 
 Timber dams, use of, 202 
 
 where applicable, 202 
 
 conditions of stabiUty, 203 
 
 water-tightness, 204 
 
 types of, 204 
 
 limits of height of, 209 
 Topographic features of arid region of 
 U. S., 10 
 
 surveys for lateral systems, 104 
 Towers, gate, 250 
 Transportation facihties, 283 
 Trestle flumes, 84 
 
 Truckee-Carson project, loss by seep- 
 age, etc., 160 
 Tunnels, 89-92 
 
 lining for, 91 
 Turbines efficiency of, igi 
 Turnouts, 67 
 Typical masonry dams, 245 
 
 Umatilla project. Ore., dam, 246, 249 
 
 loss by seepage, etc., 159 
 Uncompahgre Valley tunnel, 89 
 Underground drainage, 136 
 Underflow of streams, 118 
 Undulating areas, 103 
 Uniformly sloping planes, 103 
 United States, arid regions of, 8 
 early irrigation works in, 3 
 origin of water rights in, 264 
 rainfall of, 19 
 
 Reclamation Service canals, 47 
 Service, specifications for ex- 
 cavation, 50-52 
 Units of water measurement, 27 
 Upper Deerflat Reservoir, Idaho, dam, 
 
 24s 
 Upward pressure in masonry dams, 239 
 
 Valves, gate, 256 
 Vegetable growth in canals, 166 
 Velocities and grades in canals, 44 
 Velocity and flow of water in flumes, 
 88 
 of streams, measuring, 31 
 Vibration of outlet gates, 253 
 
 Wasteways, 79 
 
 Water, "beneficial use" rule, 267 
 
 common property of aU, 265 
 
 cushions, 75 
 
 deUvery schedule at ViUiston, N. 
 D., plant, 157 
 
 distribution, 152 
 
 continuous flow system, 153 
 
 periodic rotation system, 154 
 
 duty of, definition, 157 
 
 loss in transit, 52, 53 
 
 losses, measurements of, 159 
 
 measurement, methods, 30 
 
INDEX 
 
 293 
 
 Water measurement, units of, 27 
 methods of measuring, 27 
 plane portrayal, 147 
 points of delivery, 109 
 power for pumping, 125 
 proper amount to use, 158 
 rights, definition, 263 
 
 origin of in U. S. , 264 
 
 riparian rights, 266 
 
 acquisition of, 268 
 
 theory upon which granted, 271 
 
 apart from lands, 273 
 state control of, 266 
 soluble salts in, 33 
 supply, amount required, 34 
 
 for pumping systems, 117-119 
 
 permanence of, 280 
 
 priority of appropriation, 266 
 
 measurement of, 26 
 
 quality of, 33 
 
 source and character of, 15 
 
 study of, 18 
 
 Water-tight face of earth dams, 221 
 -tighting rock-fill dams, 230 
 -tightness of timber dams, 204 
 under-ground fallicies concerning, 
 
 118 
 used, measurement of, 160 
 velocity and flow of in flumes, 88 
 -shed, character of, 22 
 -sheds, varying runoff on, 23-25 
 
 Weight of masonry dams, 241 
 
 Weirs, rectangular and Cippoletti, 11 1 
 use of, 98 
 
 Wells, test, for drainage, 150 
 
 Williston, N. D., schedule of water 
 delivery, 157 
 
 Windmills, 123 
 
 Yadkin river, discharge of, 16, 17 
 Yakima project, loss by seepage, etc. , 
 
 160 
 Yuma siphon, 95