(Qntncll Ittiueraitg ffiibrarij Jtljata, INetn ^otk BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND THE GIFT OF HENRY W. SAGE 1891 TC 970.E46"919 '■""'""•'""'^ ^"9'"eering for land drainage; a manual f 3 1924 004 003 103 ^^s Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004003103 Engineering For Land Drainage A MANUAL FOR THE RECLAMATION OF LANDS INJURED BY WATER By CHARLES CLE A SON ELLIOTT, C.E. Member Americani.Society of Civil Engineers; Consulting Drainage Engineer; Author of "Practical Farm Drainage'' ; formerly Chief of Drainage Investigations, U. S. Department of Agriculture THIRD EDITION. REVISED TOTAL ISSUE ELEVEN THOUSAND NEW YORK JOHN WILEY & SONS, Inc. London: CHAPMAN & HALL, Limited 1919 Copyright 1903, 1912, 1919 BY CHARLES G. ELLIOTT COMPOSED AND FRINTBn BY THE PUBLISHERS PRINTING CO., NEW YORK, U.S.A. PREFACE TO THE THIRD EDITION In this, the third edition of " Engineering for Land Drainage," the author has revised some parts and added to others to make the book more useful to students and to drainage engineers. The discussion of the hydraulics of flow in underdrains has been rewritten, and new tables for the discharge of tile drains have been introduced which it is believed correspond quite closely to results obtained in practice. A diagram to facilitate the application of Kutter's formula in the design of ditches and canals has been added, as well as historical drainage matter, and a more complete text on drainage by pumps and on the drainage of irrigated lands. C. G. E. Washington, D. C, May, igig. PREFACE Since the preparation of the first edition of this book in 1902, the development and extension of land drainage have been continuous and substantial. In the course of this progress much additional data of use to engineers have become available. Increased demand for engi- neering service in reclamation projects has drawn into the field those with more or less experience in other branches of engineering as well as many just out of college. These are seeking the best information ob- tainable upon the underlying principles of drainage and methods of work. This edition of "Engineering for Land Drainage" is a new book, having been entirely rewritten. It em- bodies the essential features of drainage engineering in this country at the present time, with the latest de- velopments along each line, and is adapted to the use of the professional engineer and the student. The publications of Drainage Investigations of the U. S. Department of Agriculture are an important addi- tion to the drainage literature of the day, and I am indebted to them for miach helpful data and useful information for which credit is given wherever used in this work. VI PREFACE I take this opportunity to cordially thank A. D. Morehouse, Assistant Chief of Drainage Investigations, Arthur E. Morgan and L. L. Hidinger of the Morgan Engineering Firm, Memphis, Tenn., and S. M. Wood- ward, Professor of Hydraulics, Iowa State University, for valuable suggestions; and also, to express my deep obligations to my wife for her service in completely editing the manuscript and correcting the proof. Washington, D. C. Charles G. Elliott. November, 191 1. CONTENTS PREFACES . . ILLUSTRATIONS PAGE iii, V CHAPTER I DEVELOPMENT OF LAND DRAINAGE i The English Fens . i The Black Sluice District . . 4 Haarlem Lake .... 7 France and Italy .... 14 Field and Farm Drainage 14 Use of Drain-Tile in Europe ... . . 15 Drain-Tile in the United States . 16 Drainage in the South ... 17 The Westward Movement 17 The Present Outlook 18 Government Aid and Encouragement 18 Present Government Assistance . . . . 19 State Drainage Laws ... . 20 Advance in Methods 20 CHAPTER n THE DRAINAGE ENGINEER . . 22 Qualifications . .22 Association with Public Boards 24 Professional Enthusiasm 25 Notable European Drainage Engineers 25 Opportunities for Professional Improvement .... 27 vii VIU CONTENTS CHAPTER III VAOE ENGINEERING TECHNIQUE 29 Field- Work Equipment 29 Leveling 32 Stadia Work 35 Compass Work 35 Keeping Compass Notes . . ..'..... 40 Location of Stadia Points .4" Survey for Contour-Lines . 41 Office Equipment 45 Preparation of Maps ... 46 Plotting Angles and Locating Points . 48 Conventional Topographic Signs . ... . 51 Profiles 52 Copying Majps . -52 Reports and Estimates 54 CHAPTER IV DRAINAGE AND HOW ACCOMPLISHED 57 Soil-Water -57 Open Channels as Drains -58 Underdrainage 59 Sources of Water in the Soil 61 Relation of Soils to Drainage 62 Conservation of Moisture 62 Beneficial Effects upon the Soil 63 Visible Results of Drainage 6q CHAPTER V THE PRELIMINARY SURVEY 65 Preparatory Inspection 66 Preliminary Instrument Work 67 For Farm Lands 68 For Valleys 69 For Swamps 70 Records of Survey 71 CONTENTS IX CHAPTER VI UNDERDRAINS AND THEIR LOCATION The Outlet Principles Governing Location System of Drains . Depth of Drains Frequency of Drains Staking out Lines . Designation of Drains Taking Levels . Establishing Grade Lines Construction Figures . The Map ... Reduction Table . CHAPTER Vn FLOW IN UNDERDRAINS .... Effect of Gravity .... Velocity Formulas for Flow of Water Formulas for Flow in Tile-Drains Poncelet's Formula Modifications of Formula Illustrative Examples CHAPTER VHI THE RUNOFF FROM UNDERDRAINED AREAS Drainage Coefficient of Underdrained Soils Conditions Governing Runoff The Drainage Coefficient a Variable Examinations in Illinois and Iowa .... Coefficient for Dense Soils page; 73 73 74 76 78 8o 8i 83 83 85 87 88 92 93 93 94 97 lOI 102 105 107 108 109 109 III 116 CHAPTEI^ IX SIZE OF TILE-DRAINS 118 Application of Formulas 118 Illustrative Examples 118 Tile Mains, size of 121 Illustrative Example 123 CONTENTS Size of Laterals ' . Limitations of Size, Grade, and Length Tabulating Tile ... Preliminary Estimate of Tile per Acre . Data and Tables for Reference PAGE 124 125 125 127 127 CHAPTER X SELECTION OF DRAIN-TILE 133 Common Clay Tile ... 133 Vitrified Tile ... 134 Junction Tile . . . . i34 Large Tile • I35 Relation of Absorptive Property and Strength . 137 Porosity of Drain-Tile . . . 139 Concrete Tile . 141 CHAPTER XI CONSTRUCTION OF TILE-DRAINS Grading Excavating Trenches . Laying the Tile Inspection .... Protection of Outlets . Surface Relief-Ditches Accessories .... Difficulties in Construction Cleaning Tile-Drains . Specifications and Contracts 143 143 145 147 148 148 149 150 153 156 157 CHAPTER Xn FLOW IN OPEN CHANNELS 162 Velocity of Flow 162 Formulas for Flow 163 Kutter's Formula 164 Value of n . . .' 164 Elliott's Formula 168 Relation of Depth and Velocity 170 CONTENTS xi CHAPTER XIII THE RUNOFF FROM LARGE AREAS . PAGE . ■ . . 172 Evaporation 172 Relation of Soil to Runoff 173 Runoff Investigations 175 In Louisiana ... .... . 175 In Mississippi . . ... . 181 In Arkansas . . . . 185 In Illinois . . .188 Relation of Drainage Coefficient to Area 190 How to Select the Drainage Coefficient . 191 Drainage Curves 197 CHAPTER XIV LOCATION AND CONSTRUCTION OF OPEN DITCHES . 201 Staking the Line ... . . . 201 Establishing the Grade 202 Depth of Ditches . ..... 203 Computing the Size . . 204 Illustrative Examples 204 Side-Slopes . . 206 Berm .... 206 Dimensions of Small Ditchfes . . . 207 Cross-Sectioning . . 208 Keeping Cross-Section Notes 210 Computing Excavation ... 210 Illustrative Examples 211 Right of Way . ' .... 212 Bridges 223 Water-Inlets 223 Roadway on Bank 224 Construction . . 224 Sides of Ditch 225 Ditching Machines • 220 Specifications 228 Camping outfits 230 PAGE . . . 232 . . . 232 . . . 235 ■ • • 237 237 • 239 . 241 . . 241 Xll CONTENTS CHAPTER XV PROBLEMS IN OPEN-DITCH WORK Curvature of Ditches Erosion . . ... Decrease of Flow Due to Obstructions Cutting off Bends in Crooked Channels Waterway Between Levees Effect of Weirs and Dams Raised Outlets CHAPTER XVI DRAINAGE DISTRICTS 244 Drainage Laws ... 245 Survey and Report 245 Estimate of Costs 246 Appraisal of Damages 247 Assessments of Benefits . 249 Principles Underlying Assessments 250 Methods of Assessing Benefits 252 Arbitrary Assessment of Cost 253 Assessment of Cost According to Value of Property 254 Flat Rate or Uniform Charge per Acre 254 Difference in Value Before and After Drainage . . 255 Distribution of Cost by Division of Lands into Classes 2^ Classification by Comparison on a Basis of 100 . . 259 Assessment According to Per cent of Benefit . 260 Assessment of Irrigated Lands . . . 270 Conclusion 271 Assessments of Railroads 271 Assessments of Public Highways 272 Assessments of Town Lots 273 CHAPTER XVII LEVEE DRAINAGE SYSTEMS 275 Protection and Drainage of River Bottom-Land . . . 275 Preliminary Survey 276 The Location of the Levee . 276 CONTENTS XIU Dimensions Construction Survey . Construction ... Borrow-Pit and Berm . Intercepting Drain Maintenance Interior Drainage Sluices . Sluice Gates Diversion Ditches Drainage by Pumps Location of Pumping Station Type of Pump . To Determine Size of Pump Horse-Power Required Drainage Coefficient . PAGE 278 279 279 280 281 281 283 284 285 285 287 287 288 289 291 291 CHAPTER XVIII RECLAMATION OF TIDAL LANDS . . Causes of Failure Relation of Water-Table to Vegetation Shrinkage of Marsh Soils Dikes . Capacity of Ditches Required Construction of Sluices ... Illustrative Plan of Reclamation 294 294 295 296 297 297 301 304 CHAPTER XIX DRAINAGE OF IRRIGATED LANDS 306 Conditions which Produce Seepage 307 Preliminary Examination 308 General Drainage Plans 310 Outlets 312 Depth and Kind of Drains 313 Capacity of Drains Required . .... 314 Construction . ... 316 Gravel Covering 316 XIV CONTENTS PAGE Sand-Traps . . 316 Relief-Wells . 317 Removing Alkali . 318 Reclamation of Yakima Indian Reservation . . 319 CHAPTER XX DRAINAGE OF PEAT AND MUCK LANDS .322 Peat Lands of Europe .... Peat and Muck Lands in the United States Drainage Coefficient . . . ... Sand Subsoil ... Clay or Muck Subsoil Settling or Shrinkage CHAPTER XXI CONTROL OF HELL WATERS Drainage by Proper Plowing . Preventing Concentration of Water , Tile- Drains Needed Level Terraces . The Mangum Terrace 323 324 325 325 326 326 Regulation of Water .... . 327 329 330 330 331 332 333 Junction of Hill Watercourses with Main Stream 335 CHAPTER XXn DRAINAGE OF HOME SURROUNDINGS 336 Lawns and Grounds Gardens Orchards Cellar-Drains Roof-Water Stock- Yards Paddocks and Pastures Village Drains -,,3 Road Drainage . . ■i^n 336 336 336 337 337 337 338 CONTENTS XV CHAPTER XXIII PAGE ESTIMATES AND ACCOUNTS 341 Preliminary Estimates 342 For Owner's Benefit 343 For Boards of Assessment 344 Specific Estimates 346 For Tile- Drains . 347 For Open-Ditch Systems . . 348 Accounts and Records 349 Engineer's Charges ... .... . . 350 Code of Ethics . . 352 RECORDS NO. I. — Size of Tile Outlets in Illinois . 112 2. — Size of Tile Outlets in Iowa ... . 113 3. — Rainfall in Illinois ... .... 114 4. — Rainfall in Iowa . . . 115 5. — Breaking Strength of Clay Tile . . . 137 6. — ^Amount of Absorption and Crushing Strength of Clay Tile 138 7. — Rainfall and Runoff, New Orleans Tract 177 8. — Monthly Rainfall, New Orleans 178 9. — ^Rainfall and Runoff, Hopson Bayou, Miss. . .182 10. — Rainfall in Mississippi 183 II.— Rainfall and Runoff, St. Charles Parish, La. . . 184 12. — Relation of Drainage to Rainfall, Same Tract . . 185 13. — Rainfall and Runoff, Boggy Bayou, Ark. . . 187 14. — Rainfall and Runoff, Vermillion River District, 111. 189 15. — Flood Discharge and Rainfall in Middle West and South 192 TABLES NO. I. — Decimals of a Foot in Inches . . 89 n. — Falling Bodies 94 m. — Discharge Necessary for Various Drainage Coefficients 120 IV. A — Areas Drained by Tile Mains . ... .122 IV. B — Areas Drained by Tile Mains . 122 V. — Limit of Size of Tile to Grade and Length . 126 VI. — Square Roots of Numbers from . I to 20. . 128 Vn.— Areas of Tile 129 XVI CONTENTS PAGE Vni. — Head in Inches and Decimals of a Foot .... 130 IX. — Foot in Decimals of a Mile 131 X. — Specifications for Standard Sewer-Pipe . . .136 3t- — Values of Coefficient c 166 XII. — Mean Velocity of Water in Ditch at Different Depths . 170 Xni. — Relation of Width and Depth of Channel to Velocity 171 XTV. — Excavation and Embankment 213 XV. — Acres Required for Right of Way for Ditches . . . 222 XVI. — Curves and Radii . 232 ILLUSTRATIONS FIG. I. — Map of Black Sluice Level 2. — Map of Haarlem Lake 3. — Folding Self-reading Rod 4. — Stadia and Level-rod . . . . 5. — Leveling . . . . 6. — Taking Compass Bearings 7- — Obtaining Meridian by Equal Shadows 8. — Topography by Contours 9. — Portion of Map of Levee Districts 10. — Title of Map of Levee Districts II. — ^Title of Farm Drainage Map 12. — Plotting Compass Notes . 13. — Conventional Topographic Signs 14. — Natural System 15. — Herring-bone System 16. — Gridiron System 17. — ^Grouping System 18. — Double-main System 19. — Elkington System .... 20. — ^Guide-stakes and Hubs 21. — Profile of Main A 22. — Section of Farm Drainage Map, No. i 23. — Section of Farm Drainage Map, No. 2 24. — Guide-line for Grading . ... 25. — Methods of Using Grade-line 26. — Guides for Trenching Machine 27. — Making Curves and Junctions 28. — Plan for Concrete Outlet Protection 29. — Stone Bulkhead for Tile-drain Outlet 30. — Tile-drain with Surface-relief Ditch 31. — Surface-inlet of Broken Stone 32. — Sewer-pipe Inlet . . ... PAGE 5 9 30 31 32 37 39 44 47 49 50 51 53 76 77 77 78 79 79 82 85 90 91 144 145 146 147 149 150 151 152 152 XVIU ILLUSTRATIONS FIG. PAGE 33. — Combined Inlet and Silt-basin i53 34. — Wooden Sand-trap . i54 35. — Discharge Diagram for Ditches Opposite . . . 168 36. — Rainfall and Runoff, New Orleans Tract, Dec, 1909 174 37. — Rainfall and Runoff, New Orleans Tract, July, 1910 175 38. — Rainfall ;vnd Runoff, New Orleans Tract, March, 1911 176 39. — Rainfall and Runoff, Hopson Bayou .... 180 40. — Rainfall and Runoff, Boggy Bayou 186 41. — Rainfall and Runoff, Vermillion River District, III 190 42. — Drainage Curve No. i 198 43. — Drainage Curve No. 2 199 44. — Side-slopes ^ to i 206 45. — Setting Slope-stakes ... 208 46. — Slope-stakes on Uneven Ground 209 47.— Proper Curve for Open Ditches 233 48. — ^Action of Current on Ditch Banks at Curves . 234 49. — Proper Junction of Shallow and Deep Ditches . 236 50. — Cutting Off Bends in Crooked Channels . . 238 51. — ^Waterway between Levees 240 52. — Raised Outlet .... ... 242 53. — Map of Drainage District No. 4 26S 54. — Cross Section of River Levee . 282 SS.^Map of an Illinois Levee District 286 56. — Plan of Drainage Pumping Plant . . . 290 57. — Elevation of Drainage Pumping Plant .... 292 58. — ^Tidal Marsh Reclamation . .... 304 59. — Drains on Irrigated Tract in Colorado . . .311 60. — ^Box Drains .... 313 61. — Gravel Covering to Prevent Entr.^.nce OF Silt . . 316 62. — ^Twelve-foot Relief- well with Tile-drain Outlet 317 63. — Gravel Relief-well under Tile-drain . 318 64. — Drainage Ditches on Yakima Indian Res'n . . . 320 65. — Level Terrace 333 66. — ^The Mangum Terrace 334 Engineering for Land Drainage CHAPTER I DEVELOPMENT OF LAND DRAINAGE The importance of agricultural drainage will in a measure be appreciated when we consider the number and magnitude of land-drainage projects which have been worked out during the century which has just closed. The immense tracts of land in the Old World which have been reclaimed from the inroads of river and sea, and are now great food-producing lands, fur- nish abundant evidence of the skill of the engineers who planned and directed the work, and of the energy and persistency of the people who were responsible for its execution. The English Fens. The Fens of Eastern England, comprising over 680,000 acres of land which was formerly periodically inundated by the storm-tide of the North Sea and by rivers which discharged the waters of the interior of the island upon them, are now productive lands, dotted by thrifty towns and traversed by rail- roads of national importance. Their reclamation, which extended over a period of two centuries, was attended with difficulties and discouragements which have rarely been exceeded in the attempt of any people to enlarge its agricultural domain. I 2 ENGINEERING FOR LAND DRAINAGE The name is of Anglo-Saxon origin, corresponding in meaning to our marsh or swamp, and has come to be ap- pHed almost exclusively to the great level delta of Eastern England. The lands belonged originally to the Crown and were partially occupied by a hardy race called Penmen who, at the close of the Roman occupa- tion, 420 A.D., began to settle in what was then called the Fenland. A slightly elevated place was selected by some family or tribe and surrounded by a bank to secure it from -winter floods. This formed the nucleus of a colony which used the low lying lands for the grazing of stock and the wilder and more swampy portions for hunting and fishing. The Penmen fed a precarious life, their dwellings being subject to overflow by water which came down from the rivers and by the extremely high tides which have always been a menace to the coast lands of the North Sea. At such times the entire Fenland was submerged and the inhabitants with their cattle were obliged to seek a refuge on higher land. The people who occupied these lands were what we would call "squatters." They paid no rent but occu- pied the lands by sufferance of the Crown. When the Crown granted to others, at that time called "ad- venturers" or "undertakers," the right to reclaim the lands, they were regarded by the Penman as usurpers and enemies and often destroyed costly dikes and sluices after the lands had been drained and successfully cultivated. The Fens a National Asset. While the reclamation of the Pens, which was worked out slowly and under great difficulties, was of great national importance, no government assistance nor protection was given to those who had the courage to undertake the drainage of any part of them. The King granted to certain individuals at various times the right to reclaim tracts of land and DEVELOPMENT OF LAND DRAINAGE 3 to receive as remuneration for their labor and expense title to a portion of the reclaimed area, usually about one-third or one-fifth part. Great losses were some- times suffered by these enterprising men by reason of the failure of the Government to secure them from the depredations of the hostile Fenmen. The productive possibilities of these lands had been proven quite early in their history. During the time they were in pos- session of the Romans, great quantities of grain were grown on the borderlands and shipped out to supply their armies. It is related that in 359 a.d. a large fleet of vessels was built in the upper Rhine for the purpose of transporting food to the armies and as soon as completed was sent to Britain and loaded with wheat. Since their reclamation, the "lowlands," or "black lands," of Eastern England have remained a constant source of grain supply for the empire and as such are destined to be an area of national importance. Viewed from the standpoint of the individual farmer, agricul- ture in the Fens has been subject to uncertainties and disappointments. The history of the various stages of the improvement discloses the fact that the profits from farming, and consequently the value of the land, have fluctuated greatly, due to causes which may develop in any country. Land values in England are measured by annual rentals. Land is worth to the owner what rental the tenant can pay. That amount depends upon the cost of labor, the crop yield of the land, and the price he gets for his product. A series of wet seasons and unfavorable climatic conditions lower rentals as do also low prices of products for a term of years. As to the increase in the value of lands in the Fens as a result of their reclamation, there is no question, notwithstanding the fact that we have no figures that show the actual total cost of the work. VV. H. Wheeler 4 ENGINEERING FOR LAND DRAINAGE discusses this subject quite fully in his "History of the Fens of South Lincolnshire." The value of the Fens in the middle of the seventeenth century, before attempts were made to reclaim them, was estimated at about eight cents an acre (rental). After the work then planned was completed as stated in a petition made to the House of Lords, the value of the land was $3 to $3.75. A century later, soon after the enclosure and reclama- tion of what was known as the Holland Fen, a member of the Enclosure Commission placed the annual per acre value of 22,000 acres at $3.75, the value before improvement having been about 75 cents. In 1849 Mr. Clark, of the Royal Agricultural Society, estimated the Fenland at $10 an acre. From 1875 to 1895, there was a marked depression of agriculture in England, during which time, according to several authoritative reports, rentals fell off 25 per cent to 40 per cent. The decline is accounted for first by a series of wet seasons, 1874 to 1882, during which time the land deteriorated in production, and, secondly, to the decline in the price of products, particularly between 1882 and 1895. Dur- ing the long time in which the reclamation of the land was being worked out, the drainage was frequently shown to be deficient and the dikes and banks unable to withstand the erratic and violent high tides of the North Sea. The works were constructed by hand labor, often with insufficient funds. Discouraging losses occurred. It was only through the persistence of suc- cessive generations that the Fens have been brought to their present value and security against the ravages of tide and weather. The Black Sluice District. To illustrate some of the features of Fenland drainage, a map of the Black Sluice District,* which is tributary to the Witham River in * From Wheeler's "History of the Fens of South Lincolnshire." DEVELOPMENT OF LAND DRAINAGE 5 South Lincolnshire, is shown in Fig. i. It is a strip of level marsh, the southern part originally a lake, about four miles wide and twenty-one miles long. The LEGEND Pumping Stations tvro shown, fhus ® Boundary of Districts " " •— — — The fignrSB 10.Ii etc. show the height of the land above mean.sea level in feet. MAP OF BLACK SLUICE LEVEL LINCOLNSHIRE ENGLAND SCAtE OF MILES T~ 1 Fig. I. 6 ENGINEERING FOR LAND DRAINAGE taxable area of the district is 64,854 acres, but the total area of land which discharges its water into the ditches and through the outlet sluice into the Witham River is 134,351 acres. This area passed through successive stages of improvement from 1633 to 1886, at which latter date the system which is now in operation was per- fected. It is here proposed to briefly state some facts and lessons which we may derive from the history of those works. The main drain, called the "South Forty Foot," is 21 miles long, has a grade of 3 inches per mile, and discharges into tidewater near Boston through the Black Sluice, which has three gates each 20 feet wide. The interior drainage is accomplished through the organization of small districts bearing local names, as "Morton Fen," "Dowsby Fen," etc., which use the main drain as an outlet and pay a tax for its construc- tion and maintenance. The amount of tax for the construction of the main drain was assessed on the theory that the land most distant from the outlet should pay the greater tax. It was learned in this district, as well as elsewhere in the Fens, that the common effect produced on all Fenlands by improved drainage is a general subsidence of the soil. The removal of water from the land causes the spongy soil to consolidate or shrink gradually and the process is further assisted by plowing and cul- tivating the land. The organic matter accumulated during many centuries decomposes by being exposed to the atmosphere, and a general result is a lowering of the level of the surface of the ground. Owing to this natural and now well understood effect, gravity drains which were effective for a term of years lost their value and some of the districts were compelled to install pumps to lift the water from the lowlands into the main DEVELOPMENT OF LAND DRAINAGE 7 ditch. Numerous pumping stations are now operated to accomplish the drainage that is desired. Wheeler states that these lands have settled from 4 feet to 6 feet since 1743. The results of observations quoted by Mr. Wheeler are that the Fens in general have shrunk from 5 feet to 8 feet since their reclamation began. The uplands, comprising about 70,000 acres, shed their surplus waters into the district through small streams, which in some cases are carried across the Fens on a higher level and discharged directly into the "South Forty Foot." Such streams carry "live water " from the hills and are called "lodes." During dry seasons water is taken out of the "lodes" through small gates to replenish the drainage ditches to prevent the land from becoming too dry. It is generally conceded that the water table in peat lands should be kept within 24 inches to 30 inches from the surface. The hill lands have a chalk subsoil which rapidly absorbs the rainfall and substantially lessens the surface run-off that would otherwise take place. As a result, a considerable and constant supply of seepage water appears at the base of the slope where it is intercepted by a ditch called the "Car Dyke," which extends along the base of the slope and discharges its water into the river through an independent sluice. The elevation figures on the map show how low the land is and the little fall that the drains have. Long and costly experience has shown that all of the ditches must be kept free from obstructions at all times, or they will fail to lead the water to the outfall. Haarlem Lake, Holland. The Dutch people have been looked upon in modern times as masters of the science and art by which an important part of their dominion has been recovered from the sea. The drainage of Haarlem Lake is a striking example 8 ENGINEERING FOR LAND DRAINAGE of their ability and painstaking skill in this field of activity. Haarlem Lake was a body of fresh water oblong in shape, about i^yi miles long, 8 miles at its greatest width, and 13 feet deep. It was separated from the North Sea by a strip of land 5 miles wide, one-third of which was fertile land and the remainder sand-dunes sparsely covered with scrubby trees. Opposite the north end, about one mile distant, is the city of Haarlem, and on the east, 4 miles distant, is Amsterdam, the capital and metropolis of the kingdom. The lake, covering an area of 43,700 acres, was made to serve as a collecting basin for waters of the surrounding lands which were drained. Owing to severe storms, which rendered the overflow sluices insufficient, and to heavy rainfall in that country, the lake overflowed at times to the great injury of the adjoining lands. In conse- quence of this damage the States-General in 1839 decreed the drainage of the lake and appropriated $2,235,000 to carry out the work, and placed this work in charge of a Commission of thirteen, composed of engineers, landowners, and state counsellors. Prior to beginning operations under the commission, the details of the entire plan which was finally adopted were care- fully worked out. A survey of the bottom of the lake was made from the surface of the ice and the total volume of water that it would be necessary to pump was estimated, including the increase from rainfall and seepage. The size and arrangement of ditches, number and location of pumping stations, as well as the power that would be required to empty the lake, were carefully estimated. The plan was to build a bank or levco entirely around the lake, a distance of 37 miles, and construct outside of this a navigable canal into which the water of the lake DEVELOPMENT OF LAND DRAINAGE ^,lY>rQ.iTishse Canals are showJi thus m M Roads (First Class) '-' '• __ MAP SHOWJNG METHOD USED FOR DRAINAGE OF HAARLEM LAKE HOLLAND 8CALE OF FEET 6000 lO.ffljO 15,000 20,000 6C>>LE OF MILES Fig. 2. lO ENGINEERING FOR LAND DRAINAGE was to be pumped. When the water in the canal should become higher than the navigable level, the surplus would pass northward to the North Sea Canal through gates at Spaarndam and at Halfweg, and southward to the river Rhine through those at Katwig. The dimensions of this canal were as follows; Width of bottom 95 ft- Width of top 140 " Side slopes 2 to i Top of bank above high water 9.6 ft. Depth of canal from top of bank 17.4 " Width of top of bank 13 " A roadway was located between the canal and the levee. The canal occupied 665 acres and the bank with its slopes and the road 1,030 acres. The levee and canal were begun in 1840 and finished, except the closures, in 1843. Owing to delays in the adjustment of the rights of the owners of the surrounding lands which had formerly drained into the lake, the closures were not completed until 1848. The cost of the levee and canal was $807,500. Three pumping stations were located: one at the north extremity of the lake, one at the south, and one at the west side, each to have a 350 horse-power plant. Each plant consisted of a group of plunger or bucket pumps operated by huge reciprocating beams. The first of these was set up at the south end of the lake in 1845 and thoroughly tested. The engine worked II cylinder pumps, each 63 inches in diameter, the plunger having a lo-foot stroke and a speed of 10 strokes per minute. One stroke of the 11 pumps combined will lift 2,376 cubic feet of water a height of i6>^ feet. In a run of twenty-four hours 1,069,000 tons of water an- raised and ilelivered on a large floor from which it flows in ;i cascade into the receiving canal at the side. DEVELOPMENT OF LAND DRAINAGE II Similar pumps with 8 cylinders each were placed at the other two stations. The lake was pumped dry in July, 1852, the plants combined having been operated 39 months. It is claimed that the actual working time of the pumps was only ig}4 months. The total quantity actually pumped was 831,000,000 cubic meters against 764,000,000 originally calculated. In establishing the depth of the ditches, it was decided to fix the height of water level at 30 inches for grass and pasture lands, and 40 inches for cultivated land. Some portions of the lake bottom are sandy and there it has been found desirable to allow the water to rise within 24 inches of the surface. Since settling takes place after the water has been removed from the soil, 13^ inches were allowed for shrinkage. Two main drains 82 feet wide on the bottom were made, one north and south through the middle of the lake bottom, and the other east and west across it leading to the three pumping stations. Main ditches were made parallel to the trunk drains which lead to the pumps, each being 18 inches less in depth, and 26 feet wide on the bottom. Those running north and south were i}4 miles apart, and those east and west were placed 2 miles apart. The grades of the ditches were level, the velocity of flow being produced by the slope of the surface of the water, caused by drawing the water down at one extremity. Two inches slope per mile is allowed, and is considered sufificient to produce the required velocity. The land between the main ditches was then divided by boundary ditches into fields of 50 acres. Roads were located midway between the main ditches north and south, each having a large ditch on one side, and a small one on the other. Roads were also made along the east and west ditches. The water line of the soil in the fields distant from the main drains is economi- 12 ENGINEERING FOR LAND DRAINAGE cally controlled by making the distant ditches of less depth than the mains, so that when the water is lowered to the desired limit in the main the smaller ditches will be nearly or quite empty. The extent of the works which were required in the reclamation of Haarlem Lake may be concisely stated as follows: Length of encircling canal and levee 37 miles' Total length of large collecting canals leading to pumps . . 18.6 " Total length of main canals 93.1 " Total length of all canals and drains 750 " Total length of roads 122 " Number of bridges 65 Number of pumping plants 3 The works for the drainage of the lake deliver the water into the "Ringvart," or encircling canal. During the greater part of each year the surplus from the canal flows by gravity through sluices into the North Sea Navigation Canal, but during a part of every year the surplus must be lifted by pumps a second time. For this purpose a large pump is located at Halfweg, at the northern extremity of the lake, that raises water into a canal that connects with the North Sea Canal; a second at Spaarndam, which sends the water into the same canal, and the other at Katwig, which controls the height of the canal at the south end of the lake. The pumps at these stations are of the Scoop ^\■heel type operated by steam. A part of the expense of operating these secondary stations is charged against the property in the lake. This' account would lack an essential feature if a statement of the cost were omitted. After the reclama- tion was completed the lake bottom was sold by the Government at public auction, at prices ranging between DEVELOPMENT OF LAND DRAINAGE 1 3 $63 and $130 per acre, the average price for the entire lake bed being $80 an acre. Amount expended in actual construction $3,907,500.00 Interest charges, commissions, and amortization of capital 1,838,250.00 Total cost of reclamation S5i745i7So.oo Amount derived from sales of land, rents, etc 3,907,000.00 Net cost to Government $1,838,750.00 From these figures it appears that the net cost to the Government, after credits were deducted, was $42 per acre. The average annual rainfall is 32 inches; the maximum 40.16 and the minimum 26.7. There are occasional instances on record when the rainfall for a single month was as much as 6 inches. The pumps are usually oper- ated 94 days of 24 hours in a year, and when all are working they remove one-fourth to three-eighths inches of water in depth from the entire district in 24 hours. The annual tax for pumping and maintenance of the main ditches for some years after operations were begun was about 80 cents an acre. Fig. 2 is a map of the Haarlem Lake area as it now exists, reproduced from the government topographical survey. About 16,000 people occupy this unique do- main lying 12 feet below the level of the sea. Two towns in addition to the numerous farmsteads located along the main roads give an appearance of thrift and comfort to the entire area. The drainage of Haarlem Lake was justly regarded as a great achievement. A period of fifteen years elapsed between the beginning and the consummation of the work, though it should be understood that a consider- able part of that time was used in adjusting the rights 14 ENGINEERING FOR LAND DRAINAGE and claims of property owners outside of the lake. The sentiment which prevailed when the work was com- pleted was forcibly expressed on a medal which was struck ofif by the Government. It is in Latin, but freely translated reads: "Haarlem Lake, after having for centuries assailed the surrounding fields to enlarge itself by their destruction, conquered at last by force of machinery, has returned to Holland its 44,280 acres of invaded land. The work commenced under William I, in 1839, and has been finished in 1853 under the reign of William HL" France and Italy. Both France and Italy can point to large drainage works by means of which the area of pro- ductive land has been increased. The project of La Gironde, France, included 1,500,000 acres, and of Forez, 140,000 acres. A notable one in the provinces of Man- tua and Reggio, Italy, covering nearly 80,000 acres, cost $3,200,000, three-fifths of which was borne by the general Government, and the balance divided equally between the landowners and county governments. Italy depends for her cereal products as largely upon her drained areas as upon those which are irrigated. Several million acres have been made both sanitary and productive. Field and Farm Drainage. We get, however, but a distorted view of the office which drainage has per- formed in agriculture if we confine our attention to the larger, and consequently more spectacular, projects of different countries. The control and conservation of water in all agricultural lands is an essential part of their management. They increase production without increasing the labor of tillage or extending the boundary of the field. Terracing and field drainage are becoming better understood, and their Aalue appreciated in pro- portion as better methods of agriculture are practiced. DEVELOPMENT OF LAND DRAINAGE 1 5 No greater incentive to the drainage of swamps or the protection of lands from overflow can be found than the results which follow the drainage of the field whose previous returns to its owner had been meager and uncertain. Field and farm drainage by means of the universal small open-ditch method has been largely sup- plemented and in many cases supplanted by the cov- ered trench or underdrain. Trenches in which were placed stones or brush to serve as a water conduit and covered with earth' were employed a hundred years before tile were known, and demonstrated conclusively, in many instances, that underdrains were superior to open ditches. Use of Drain-Tile in Europe. The invention of clay tibs, or " land pipes," as they are called in England, for draining land, marks an important epoch in the his- tory of drainage. Faure, in his work upon drainage, holds that the use of drain-tile originated in France, but credits England with the rediscovery of this method of draining which he concedes that France had lost. The discovery of drain-tile in the Convent garden at Maubeuge, in Northern France, in 1620, supports his claim. Drain-tile were first used in England on the estate of Sir James Graham, Northumberland, in 1810. They were made in two separate pieces, the top, called the " tile," being like the letter U inverted, and the sole, a flat plate upon which the tile was placed. These ap- pear to have been the standard tile for thirty years. During this period the development of land drainage was slow. Quite indififerent success not infrequently attended the efforts of estate owners until 1840, when the experiments of Smith and of Parkes showed how tile-drainage would greatly increase the fertility of farm lands. The spread of underdraining throughout Eng- land and Scotland then became rapid. The action of 1 6 ENGINEERING FOR LAND DRAINAGE Parliament in 1846 creating a fund of $10,000,000 to be loaned to farmers, for use in draining their land, greatly promoted its development. In 1843 a machine was per- fected for molding cylindrical tile which was enthusias- tically welcomed by land drainers. The movement which began in England extended to France and Germany, where equally salutary benefits followed the underdrainage of farm lands. According to figures collected by Mr. J. H. Klippart, about $8,000,- 000 were expended in France for draining from 1850 to 1856, and during the year 1856, 85,000 acres were thor- oughly drained. It should be said in this connection that France and Germany have carried the art and science of underdrainage to greater perfection than any other countries. Drain-TUe in the United States. The United States is indebted to England, or possibly, more accurately speaking, to Scotland, for her first lessons in tile-drain- ing. Johri Johnston, a Scotchman, of Geneva, N. Y., known as the " Father of tile-drainage in the United States," introduced handmade drain-tile on his farm in 1835. By 1 85 1 he had laid 16 miles of drains with most gratifying results. In 1848 the first drain-tile machine was imported from England, after which tile were ob- tained at a price which, as Mr. Johnston remarked, left a farmer without excuse for wet land. The land which is now Central Park, New York City, consisting of 856 acres, which before improvement was regarded as a menace to the health of the city, was drained in 1858. At the time, it was the largest drain- age work in this country, and as such attracted no little attention. Col. Geo. E. Waring, the engineer, copied English methods almost exclusively, using for lateral drains i^-inch tile, with collars. His book, " Drain- ing for Profit and for Health," published in 1867, quotes DEVELOPMENT OF LAND DRAINAGE 1 7 the practice which was followed in the design and con- struction of that work. Drainage in the South. The fact should not be over- looked that prior to these dates drainage by ditches and dikes was an essential feature of agriculture in the South. The culture of rice, which was exceedingly profitable along the tidal rivers, required the construc- tion and maintenance of banks, ditches and sluices which entailed a large expense and watchful supervision, while many acres of level lands along the coast which were operated under the old plantation regime were provided with an elaborate network of ditches. No little enterprise was shown, particularly in the Caro- linas, in developing the productiveness of those level but fertile lands. Had not this progress been inter- rupted by the war, the following years would doubtless have witnessed a great expansion in drainage opera- tions. The Westward Movement. Such were the begin- nings of land drainage. They found the United States a vast and undeveloped country of unknown wealth and with agricultural possibilities which had not been dreamed of. The drainage movement, in common with other developments in agriculture, proceeded westward from New York into Ohio, Indiana and Illinois, and to a greater or less extent throughout the Middle West. The benefits of draining the fields and farms induced land- owners to extend their operations so that the cooperation of many individuals was often required in the improve- ment of creeks and other natural watercourses, and also in constructing large artificial canals, which were re- quired in draining large level areas. Drainage laws were enacted by the States, excavating machinery was perfected, numerous drain-tile factories were established, and, in short, a healthy activity in drainage character- 1 8 ENGINEERING FOR LAND DRAINAGE ized the half century following the introduction of modern methods in western New York. The Present Outlook. By reason of the vastness of our country we have before us greater drainage prob- lems and possibilities of land development than any nation in the world. More than 70,000,000 acres of un- reclaimed land await the touch of the engineer and the intelligent activity of the ambitious and enterprising farmer, whenever they are ready to begin their reclama- tion. These lands are found in all parts of the country, and offer soils of every possible description. Besides these are the enclosed and cultivated lands, the pro- duction of no small part of which may be doubled by thorough drainage. Government Aid and Encouragement. Legislative action in several instances has played an important part in promoting the reclamation of land. It cannot be denied that in the larger sense of the term the work is more or less a public function. We find that on this theory governments have participated in it by assisting in planning and directing the execution, and by advanc- ing money in the form of loans on long time for the con- struction of the drains. England greatly encouraged drainage by passing the " Public Moneys Drainage Act" in 1846. It provided a sum of $10,000,000 for Great Britain and $5,000,000 for Ireland, to be loaned to owners for draining land, the work to be done under government supervision. The loan was to be repaid with interest in equal annual instalments, the time limit allowed being 22 years. In 1849 the " Private Moneys Drainage Act " was passed. This permitted the incorporation of land-improvement companies having authority to construct drainage works and loan money for this purpose, the amount to be secured by rentals from the land. A large amount of work was done under DEVELOPMENT OF LAND DRAINAGE 1 9 these two acts in a systematic and thorough manner. France also authorized the loan of public money for draining, but it should be noted that in both countries the work proved so attractive in a few years that private enterprise rendered government loans unnecessary. Belgium and Germany went so far as to establish fac- tories and sell tile at low rates so as to place them within the reach of the majority of tenants and landowners. Experiments were conducted by these governments at various points so that all might be informed of the advantages of drainage. Assistance of this kind was given during the decade ending about 1856, since which time such work has been accomplished by individual enterprise, the governments becoming a party where the works were manifestly of public benefit. Present Government Assistance. Government aid in England at present (191 1) is limited to a law similar to the one passed in 1849. In France, the government through the Minister of Agriculture furnishes, upon re- quest of landowners, engineers to lay out and superintend the construction of farm drains free of expense to the owners. The Province of Ontario, Canada, has a law giving the Province authority to loan farmers amounts to the limit of $1,000 each for expenditures in tile- draining; these to be repaid in 20 years at the rate of $7.36 annually on each ^100 loaned. The provincial government also furnishes engineers to lay out farm drains with no cost to the owners except the traveling expenses of the engineer. The United States Government has never granted specific loans to be applied in draining farm lands. Under the provisions of the Federal Farm Loan Act passed by Congress July 17, 1916, loans may be ob- tained by owners of farms, the proceeds of which may be used for making improvements, including farm 20 ENGINEERING FOR LAND DRAINAGE drainage, and for conducting farm operations more efficiently and profitably. State Drainage Laws. To facilitate the construction of reclamation works of all classes, nearly every State has a general drainage law which gives landowners authority to effect drainage organizations of a cooper- ative character, levy and collect special assessments to defray the cost of the work and, if found expedient, to raise money by the issue of bonds secured by the lands which will be improved by the proposed work. Under the provisions of these statutes large and costly projects have been financed and the work successfully completed. Such laws provide the legal methods which have been found necessary for landowners to construct the larger drains and improvements, in which a considerable num- ber have a common interest and consent to share the costs. Advance in Methods. The development of methods of drainage is one of the most striking features of its history, particularly in our own country. The intro- duction of the land steam-dredging-machine in Illinois in 1885 was a noteworthy epoch in American drainage. The perfection of this type of machine made it practi- cable to open canals through the prairies and swamps and improve creeks effectively and at moderate cost. A variety of types of power land and floating exca^•ating machines are in successful use for constructing large canals, and power trenching machines are employed for making underdrains. Dynamite assists in preparing the way for the machines through wooded lands, and its use for the actual digging of the ditches is being developed. Cement is at hand for drainage structures, while cen- trifugal pumps operated by steam, oil or gas engines lift the drainage water where gra\ity outlets are lacking, compressed air also being used under certain conditions DEVELOPMENT OF LAND DRAINAGE 21 for the same purpose. Factories deliver clay and cement pipes for draining as large as 36 inches in diameter. These methods are in strong contrast with those which were employed half a century ago, and suggest further progress along these lines in the near future. CHAPTER II THE DRAINAGE ENGINEER The magnitude of drainage operations which are called for today, the many phases of the work, and the economic as well as engineering problems which arise in the process of developing land, make the profession of drainage engineer one which requires special training and, if faithfully followed, involves no little responsi- bility, though yielding much of enjoyment and recom- pense. The great variety of attainments which are demanded of the engineer will be apparent from a cursory view of the drainage field. It includes the drainage of fields and farms ; plans for draining swamps and bodies of level land thousands and even millions of acres in extent; the improvement of watercourses; the protection of over- flowed land by levee, and the diking of tidal marshes with the construction of the necessary ditches, sluices and pumping plants for such lands; the control of hill- side waters; and the various problems relating to the drainage of irrigated lands. Qualifications. The engineer should therefore have a quick eye for land surface and a good knowledge of soils, plants and agriculture in general, that he may detect differences in land by its topography and vege- table growth. He should be able to critically examine subsoil and other substrata and judge of their water properties, and should also be able to predict, in a measure at least, what effect draining will have upon lands and upon their value for agricultural purposes. THE DRAINAGE ENGINEER 23 An examination of this kind should give him the in- formation he needs for outlining such surveys as may be required. He should possess a full knowledge of technical engineering if he expects to handle all branches of drainage work. This of course carries with it pro- ficiency in the use of level, transit and compass. He should be conversant with practical hydraulics, the de- tails of levee building, pumping for drainage and up-to- date methods of construction. He should be able to present his work clearly, simply and logically by reports and maps, and discuss the various problems in a force- ful and intelligent manner. A part of the engineer's work is subject to the drain- age law of the State in which it is done. To guard against any possible defects in his plans he should familiarize himself with the law so that he can make his surveys and reports conform to its requirements as far as legal pro- cedure is concerned. He should be the adviser of drain- age boards upon all points of design, and upon prin- ciples and methods of assessing damages and benefits. The latter subject deserves careful and analytical thought and should include an examination of such court decisions as have a bearing upon each case. The engineer should make himself invaluable to the board by elucidating the application of the law to the various conditions which are under consideration in such a man- ner that the members can intelligently come to an agree- ment in making the adjustments which the law requires of them. An engineer should be a surveyor, but a surveyor is not by virtue of his occupation an engineer. The sur- veyor may make measurements, run levels and make maps but not be able to design an effective and econom- ical drainage system. The engineer, however, cannot wisely direct such work unless he is himself proficient 24 ENGINEERING FOR LAND DRAINAGE in the details of surveying as well as in practical de- signing. In short, he should be able personally, if necessary, to do the work from the setting of the initial stake to the completion of the plans and estimates. Association with Public Boards. The drainage en- gineer is called upon to deal with corporations, boards of commissioners and drainage associations, as well as with individuals, in his capacity of professional expert and counselor. He has facts and professional knowledge which they do not possess. He should make his em- ployers' case his own and give them the best plans and advice at his command, having due regard to sound practice and enduring results. He should be able to divest his reports of technical details to such a degree that his clients will understand the subject under con- sideration clearly and be able to act intelligently upon the proposition. It is an element of weakness on the part of the engineer to obscure his work by technicalities which he does not expect the layman to understand. Drainage is a simple, common-sense operation, the plans for which can be made intelligible to any attentive mind. The engineer is sometimes urged to modify his plans and recommendations and endorse methods which in his judgment are not wise, and often heavy pressure is brought to bear upon him from various sources in order to bring this about. Possibly changes may be made without injury, but they should be careful!}' reviewed and if they are found impracticable and ill-advised, the engineer should so represent them. It should be re- membered that the board or company expects reliable advice from the engineer and will be ready to censure him even for compliance with their wishes if he endorses a plan which, in the end, proves unsatisfactory or fails entirely. He should not be a tool in the hands of the board or any interested party, but an honest counselor THE DRAINAGE ENGINEER 25 and director of the undertaking for which he has been employed. His plans should possess such merit that they will appeal to his clients and any differences of opinion or judgment should be courteously discussed. Such a course calls for the exercise of a high order of common-sense, good judgment and integrity in addition to the technical skill required in the management of the project which has been intrusted to him. Professional Enthusiasm. He should not let his ideas of engineering precision lead him to do work which will have little practical value in dealing with the project he is working out, yet he should conduct his work in a professional way and with due regard to conventional accuracy. He should honor his profession by exhibiting a well-balanced enthusiasm in all of its branches, and by ability and trustworthiness establish himself in the confidence of all with whom he has professional or busi- ness relations. Since he comes in contact with people of diverse opinions and temperaments to whom he is ex- pected to explain his plans and to instruct in affairs relating to drainage, it becomes him to cultivate patience, courtesy and a sympathetic personality. Notable European Drainage Engineers. The Ameri- can engineer who proposes to devote his time and talents to drainage work is following in the wake of engineers of the Old World of no mean ability and repu- tation. With the reclamation of the English Fens, before referred to, are associated the names of such engineers as Cornelius Vermuiden, whose early achieve- ments in Holland drainage work led to his employment in the time of King Charles the First, and who in 1642 reported to the King a plan for controlling the waters of the rivers which crossed the fens, and who was later identified with various improvements in fen drainage. Sir William Dugdale was connected with some of the 26 ENGINEERING FOR LAND DRAINAGE earlier works. His book upon the History of Draining and Embanking contains the most complete record ex- tant of the early attempts to drain the fens. Thomas Telford, whose name is associated with road building, Sir John Rennie, who was knighted by the Crown in ap- preciation of services on the great London bridge, and Sir John Hawkshaw, all noted engineers, made examina- tions and reports on various problems connected with fen drainage. W. H. Wheeler, whose excellent works on the " Drainage of Fens and Lowlands" and " History of the Fens of South Lincolnshire" are invaluable addi- tions to drainage literature, was connected with later developments of English lowlands. Among those who were later identified with the drain- age of the uplands of England and Scotland should be mentioned Josiah Parkes, consulting engineer for the Royal Agricultural Society, and J. Bailey Denton, mem- ber of the Institution of Civil Engineers of England. The long career of the latter in directing farm-drainage operations, together with his able expositions of the theory and practice of such work, justly entitles him to the esteem which is accorded him by the English people. To this incomplete list of English drainage engineers might be added the names of many equally eminent in almost every country of Europe, notably France, Bel- gium, Germany and Italy, all of whom hare by their engineering skill in the design and direction of large drainage undertakings exerted a marked and beneficent influence upon agricultural development in their re- spective countries. It may not be out of place to mention here that unique character, Joseph Elkington, of Warwickshire, England, who, though an illiterate farmer without training of any kind, left his indelible stamp upon drainage practice. THE DRAINAGE ENGINEER 2/ He first discovered and applied a new method of draining to his own farm in 1764 and soon became noted for his skill in draining lands which were similar in character. His discovery and successful practice created such in- terest in the agricultural circles of England and Scot- land that Parliament in 1795 voted him £1000 in ap- preciation of his services. Briefly described, his method consisted in seeking out hidden springs and water currents and tapping them by means of auger holes which were made in the bottom of deep ditches. The water being under pressure rose in the holes and flowed away in the ditches. Elkington possessed the gift of locating underground sources of water and succeeded in drying bogs which resulted from seepage from higher lands and from the flow of hidden springs. The system which is known by his name is now successfully applied in draining irrigated lands in the West. The successful career of Elkington emphasizes one important qualification of the drainage engineer which does not come from college training nor is it acquired from books. It is the ability to determine the source of the trouble. This is in some degree a natural gift, but may be to a large extent acquired by close observa- tion and practical experience in investigation of soils under varying conditions. Though without book-learn- ing, Elkington possessed the practical skill which en- abled him to read soils. Opportunities for Professional Improvement. The American engineer has been compelled to modify Euro- pean practice quite materially to meet the requirements of this country. Our soil and climate are peculiar to America. Our areas to be treated are large and their possibilities are attracting the attention of owners and investors. We need but point to the mistakes that have been made during the last 25 years tp ghow that 28 ENGINEERING FOR LAND DRAINAGE the field demands the best talent which the profession can give. It is urged that engineers who lack experience, be they young or old, associate themselves for a time with some one of experience before assuming the re- sponsibility of designing a system of drainage. In any event, the subject should be studied on the ground with a care commensurate with the importance of the under- taking. It need hardly be suggested that the engineer should be a close student not only of science and nature, but of practical affairs as well. He may also with profit fre- quently systematize his methods of work and direcc his thinking along logical lines by contributing to the col- umns of technical and popular periodicals. The art of ex- pressing thought in terse and clear English and of arrang- ing subjects in a logical and orderly way is exceedingly valuable to the engineer and should form a part of his professional training and career, as should public speak- ing also, since he will frequently be called upon to address gatherings of engineers or agriculturists in the interests of drainage, and it will be a serious handicap if unable to do so readily and well. Land drainage is an enterprise of such nature that a drainage engineer may justly take pride in the fact that his labors contribute materially not only to the wealth and prosperity of the community and the country at large, but also to the comfort and health of the people and the beautifying of their homes, while the perma- nency of drainage works makes tliem an enduring monu- ment to his skill. CHAPTER III ENGINEERING TECHNIQUE Drainage engineering, in common with other branch- es of civil-engineering, demands mechanical skill in the use of such instruments as are necessary in field or office work. While the professional engineer in any branch should wholly master what may be called the technique of his profession, including a perfect familiarity with all forms of instruments employed in the work, and skill and dexterity in the various methods of using them to secure the data sought, the subject will be briefly pre- sented here, covering only the simplest and most im- portant points, with the expectation that the engineer will constantly add to his knowledge and proficiency, both by experience and by information gathered from books and other sources. Field- Work Equipment. Instrument-work in the field is required to secure the facts regarding surface levels, depth and size of watercourses utilized, location of prop- erty lines, and other data which the engineer will need in ascertaining the conditions existing, in planning the system of drainage demanded, and later, in laying out and constructing the work as planned. The equipment for field-work need not be large, but should be well se- lected. An instrument which is susceptible of more general use than any other is the engineer's combined level and transit. This should be furnished with a sensitive and well-set telescope level, stadia hairs set to cover one foot on the rod at a distance of lOO feet, plus 29 30 ENGINEERING FOR LAND DRAINAGE a constant, a compass with variation plate, and a verti- cal arc, or half circle, for measuring vertical angles. Excellent leveling can be done with such an instrument, and by using the vernier plates, compass and stadia, every variety of instrument-work required in making drainage surveys can be performed. The i8-inch Y level, equipped with stadia hairs and a detachable strident 3-inch com- pass upon the telescope, is also an instru- ment of almost general use in making drainage surveys upon level lands. The ordinary target-rod is quite essential in checking benches and in primary level- ing, but the "speaking," or self-reading rod, is the better for general use, as it can be employed for both level and stadia work. When graduated properly it can be read with distinctness by the instrument-man, thereby makirg him independent of the rodman, besides enabling him to work more expeditiously. A great many designs of such rods are in use. The style of gradua- tion that the author has found most easily and accurately read is represented by Fig. 3. This is made of a strip of straight-grained white pine, i inch thick, 2^ inches wide and 12 feet long. The ends are shod with bands of iron JiJ-inch thick to pro- tect them from battering. The rod is cut in two in the middle and a plain strap hinge set in even with the face so that the faces of the two parts can be folded together for convenience in transportation. It is held open while in use by means of a rib of wood which is fastened to the back by screws and covers the joint. A movable bolt with a thumb-nut is used to fasten the rod open or shut as desired. The dark spaces in the figure, showing tenths Fig. 3.— Folding Self-read- ing Rod. ENGINEERING TECHNIQUE 31 of a foot, are red on the rod. The foot figures are large and painted red. The tenths figures are black, and the small squares along the center line representing two- hundredths spaces, are also black. The arrangement of spaces and colors is such as to be clearly- read at a distance of five hundred to eight hundred feet, depending upon the power of the telescope and the strength of the light. Fig. 4 represents a 14-foot non-folding rod which is a favorite with engineers. It is made of straight-grained white pine 4 inches wide, %-inch thick, with a rib on the back to give greater stiffness, the ends being capped with straps of iron K-inch thick. It is painted white and black as shown in the cut, the divisions being half-tenths of a foot. It is a superior stadia rod which can be made cheaply, and is durable if covered with first- class enamel paint. The 100-foot steel wire chain with brazed links is, perhaps, the most convenient and serviceable for use in drainage surveys through a rough country, but is open to the objection that the links wear rapidly so that the chain requires frequent correction. The band chain, or steel tape, should be kept on hand as a standard by which to correct the chain and also for checking the stadia dis- tances, but its liability to be broken in the hands- of workmen, as well as the disadvan- tage in its use of requiring two hands for setting a pin at the fore end, makes it less desirable for constant use than the chain. A set of eleven marking pins should accom- pany the chain. Two or more flag-poles, steel or iron pointed, and each bearing a flag of cloth 8 in. by 12 in., Fig. 4. — ■ Stadia and Level-rod. 32 ENGINEERING FOR LAND DRAINAGE half white and half red, are needed in marking out courses for chainmen and axmen to follow when staking out lines. Machetes, or long heavy knives with handles, are best for cutting brush; these, with shoulder sacks for carry- ing stakes and hand-axes for driving them, may complete the engineer's instrument outfit for field-work. Leveling. Leveling is the fundamental and most important instrument-work connected with drainage engineering. While the operation is simple, it is easy for the instrument-man to make a mistake which will render the entire work valueless until the mistake can Fig. 5. — Leveling. be found and corrected. For this reason he should be careful to keep his level in perfect adjustment, and use a method of keeping notes which will apply to all situ- ations, since following the same routine establishes a habit of work which is conducive to accuracy. The notes can hardly be too complete or too carefully kept. In the words of an old professor, " Always put your notes down as if you expected to die before morning, and wanted to leave them in such good condition that in ten years' time, a stranger, with none of the old party to help him, could take your book and proceed on the job without delay." A method of checking work in the field should also become a habit of the level-man. A convenient size for a field-book is 4 inches by 6}4 ENGINEERING TECHNIQUE 33 inches, containing i6o pages. Two pages facing each other are required for each set of notes, the left-hand page being ruled in five columns and headed as shown below, the right-hand being open for explanations, sketches, etc. LEVEL-NOTES TO ACCOMPANY FIG. 5. Sta BS H I FS Elev A S-io 3-70 5-40 iS-io 16.00 19.20 10.00 B C D 2.80 2.20 4-25 12.30 13-80 14-95 To run a level-line, select some bench-mark or other permanent point from which it is proposed to start and establish a datum to which all levels in that survey shall be referred. If its elevation is not known, assume one which will be convenient to use without introducing minus expressions. If we begin low down on some watercourse perhaps 10.00 will do; if higher up 20.00, 30.00 or 100.00 should be used as the elevation of the starting point. If some permanent railroad or govern- ment bench with recorded elevation is within reach utilize it. Place this in the elevation column opposite Sta A (See Fig. S and accompanying notes). Set the level mid- way between this point and the next point B, or, if more convenient, on one side of the line, provided the distance from the position of the level to either point is about equal. Have the rodman hold the rod vertically at A, and with the level-bubble in the center, read the rod at the point where the horizontal cross-hair intersects it. This is called a backsight, and in the example is 5:10. Enter this in the B S column opposite Sta A ; add the backsight to the elevation of the point A, thus obtaining 34 ENGINEERING FOR LAND DRAINAGE the elevation of the line of sight through the instrument, or the height of instrument, as it is called, abbreviated on the notes to H I. In this case it is 15.10, and is en- tered in the H I column opposite Sta A. Next take a sight in a similar manner on B, called a foresight, and enter the reading in the F S column opposite Sta B. This in the example is 2.80. Subtract this reading from 15.10, in the H I column, and write the difference, 12.30, in the Elev column opposite Sta B. This is the height of B with reference to A. If the elevation of other points is desired before the instrument is moved, take as many foresights as wanted and obtain the elevation of the points by subtracting each from the H I. Next move the instrument to some point beyond B and take a back- sight on B. Record it in the B S column opposite Sta B and add it to the elevation of B to obtain the H I in its new position. Enter the sum in the H I column opposite Sta B. In the example the B S is 3.70, Elev 12.30 and H I 16.00. Take a foresight on C, subtract the reading from 16.00, the H I, and obtain 13.80, the elevation of C. Remove the instrument to a point be- yond C and obtain the elevation of D in the same way. The points upon which two readings are taken are called turning-points. All others, except bench-marks, are called intermediates. Pegs should be driven into the ground upon which to make turning-points, if more permanent ones are not at hand. This method of pro- cedure is simple and can be universally applied. The work in the field can be "checked," or proved, by re-running the line in an opposite direction, and also by occasional long backsights to stations already lev- eled, the results of whicii will indicate whether any serious error has been made. The book may be checked, first, by reviewing the additions and subtractions carefully and, second, by ENGINEERING TECHNIQUE 35 finding if the difference between the sum of the fore- sights and the sum of the backsights is the same as the difference in the elevation of the points compared. In the example just examined: Elev D = 14.95 Sum of backsights = 14.20 " A = 10.00 " " foresights = 9.25 Bifference 4.95 Difference 4.95 Stadia Work. The stadia is particularly useful for measuring distances, and is more accurate for that pur- pose than chaining as ordinarily done. The distance is found by observing what portion of the image of the graduated rod is included between the cross-hairs of the telescope. The farther the rod is from the instrument the greater is the portion of the image which falls be- tween the cross-hairs. The hairs, one on each side of the center, are so placed that they include one foot on the rod at a distance of 100 feet, two feet at a distance of 200 feet, and so on as far as the rod can be read, pro- portionate spaces included on the rod representing proportionate distances. The distance read is not from the center of the instrument but from a point in front of the center equal to the focal length of the telescope. This length, called a constant, determined by the maker and furnished with each instrument, must be added to each distance-reading to obtain the distance from cen- ter of instrument to the rod. The rod should be held vertical to the line of sight, which is easily done on level land. The use of the level-rod for stadia purposes en- ables the engineer to locate a point by azimuth, distance and elevation at one operation. Compass Work. The magnetic compass, placed either upon the engineer's transit or upon the telescope of the level, as before described, is exceedingly serviceable in making drainage surveys, and gives more accurate results 36 ENGINEERING FOR LAND DRAINAGE than are usually attributed to it. In fact, for locating "stadia shots" and in running out drain lines or locating points for various purposes after a permanent base of operations has been established to which such lines may be referred and checked, and particularly for use in a wooded or brushy country, the compass meets every requirement. It should, however, be employed for running short lines only, and where slight errors will be of no material importance. The needle indicates the magnetic meridian, an ap- proximately north and south line. The true meridian is a north and south line which if extended would pass through the north pole of the earth. The compass circle is divided into degrees and frac- tions of a degree. The letter E, denoting east, is at the left hand, and W, west, at the right hand of the box, which is contrary to the position of these letters in the small pocket-compasses. This arrangement is neces- sary because in using the field-compass the box is turned so that the sights point in the direction of the line whose azimuth is to be obtained. The north end of the needle is read, which gives direct the azimuth of the line, or the angle which it makes with the magnetic meridian. The bearing of a line is the angle which it makes with the direction of the magnetic needle. The length of a line, with its bearing, is termed its course. To take the bearings of a line, set the compass directly over a point in it, at one extremity, if possible, though this is not essential. Bring the compass to a level position. Ha^e a flag or rod set on another point of the line. Direct the sights upon this rod as near the bottom as possible. Always keep the north end of the compass ahead. It is distinguished from the south end by some conspicuous mark on the face. Sight accurately to the flag and read the north end of the needle. To do this, note first the ENGINEERING TECHNIQUE 37 N. or S. point of the compass, according to which is nearest the north end of the needle; second, the number of degrees to which it points; third, the letter E. or W., whichever is nearest the north end of the needle. Always read and record bearings in this order. To illustrate: In Fig. 6, a b is the line along which the sights point. Fig. 6- — Taking Compass Bearings. The needle points constantly to the meridian, hence in turning the sights to the line a b, the angle N b is turned off, or from o° to 35°, and the needle reads north, 35° east, hence the bearing of the line is N. 35° E. To test the accuracy of the bearing, set up the instrument at the opposite end of the line and take a backsight upon the first point. If the number of degrees read the same but with opposite letters, the bearing first taken was correct. The declination of the needle is the angle which the magnetic meridian and the true meridian make with each Other, and though constantly changing it must always be taken into account except on or near a certain line 38 ENGINEERING FOR LAND DRAINA-GE passing across the country called "the line of no vari- ation." While this line, of course, varies slightly with the changes in declination, it enters the U. S. near the eastern end of Lake Superior and passes in a south- easterly direction through Michigan, Ohio, etc., leaving the U. S. at a point on the coast of South Carolina, below Charleston. It is desirable to record lines with their true bearings, or as nearly so as practicable, though this feature of the work is not so important in drainage surveys as in those which are made for the definition and determina- tion of land-lines. The local declination can be deter' mined by setting up the compass upon an old land-line whose bearing is known, if such can be found, or in the absence of such a line, a bearing may be taken upon the pole-star and declination noted. This will be only ap- proximate, as the star is I>^ degrees from the pole, revolving about it, and is on the true meridian only twice in twenty-four hours. Another method of determining an approximately true meridian is by equal shadows cast by the sun. At some point on a level surface, as at s in Fig. 7, place an upright staff not less than 10 feet long. Two or three hours before noon mark the extremity of its shadow, as a. Describe an arc of a circle with s, the foot of the staff for center, and s a, the distance to the extremity of the shadow for radius. Shortly before the length of time after noon that it was before noon when the first mark was made, watch the shadow, and when its end touches the arc previously described mark the point, as b. Bi- sect the arc a b and mark the point n. Then s n will be the true north and south line. Set up the compass at s, sight on n or s n produced, and read the needle at that place. It is more important, however, to record on the notes ENGINEERING TECHNIQUE 39 the declination used than it is to go into the niceties of obtaining and using an absolutely correct declination angle for line work of the character herein described. If the compass has a declination plate, set off the decli- nation assumed or determined, and record all bearings as read. If there is no such provision for mechanically correcting the azimuth make corrections on the notes according to the following rule: When the variation is east, as in localities west or southwest of the line of no variation, for bearings N. and W. or S. and E. subtract Fig. 7 . — Obtaining Meridian by Equal Shadows. declination from magnetic bearing. For bearings K. and E. or S. and W. add instead of subtract. When the variation is west, as in localities east and northeast of the line of no variation, for bearings N. and W. or S. and E. add the declination, and for bearings N. and E. or S. and W. subtract. Care must be taken that wire fences or other improvements of iron or steel- are not near enough to the compass to deflect the needle and give an inaccurate reading. If necessary to obtain the bearing of a wire fence line, an offset of 30 feet may be made, and the bearing of this parallel line be read. 40 ENGINEERING FOR LAND DRAINAGE Keeping Compass Notes. The running form of keep- ing notes is simple and in common use. For example, in recording the notes of drains, the following notes may be written on the right-hand page of the level-book. DRAIN NO. 2 Sta 0- 6 N 10° 30' E Sta 6- 8 N 4° 00' E Sta 8-is N 32° 00' W Sta 15-22 (end) N 15° 20' W The same form should be used to record a continuous and connected line like the boundary of a farm or field. Backsights should be taken at each station to ascer- tain if there are any disturbing influences which cause the needle to read differently at the two ends of the line. If a discrepancy in the two readings is found, some point on the same line intermediate between the two should be used to determine which of the bearings is correct. Location of Stadia Points. For locating the position of stadia points by the transit with attached compass and obtaining their elevations at the same time, use the following method: Set the instrument over a station whose elevation is known and add the distance between the hub of the station and the center of the telescope to the elevation of the station, to obtain the height of instrument (H I). Take sights at the rod as it is held at selected points within the range of the observing station. Read the interval on the rod subtended by the stadia hairs for distance, read the position of the center hair upon the rod, when the level bubble is centered, to ENGINEERING TECHNIQUE 41 obtain elevation, and read tiie north end of the needle for azimuth or direction. Record the readings and re- sults in the following form: OBSERVATIONS AT STA 4 Elev 127.02 H I 132.42 Stadia Constant 1.31 Point Stadia Rd'g Distance, Ft. Bearing FS Elev I 6.21 2.32 389 N89°W 4-32 128.10 2 7.10 2.15 495 N46°3o'W 2.41 130.01 3 8.4T 2.41 600 N44°W 3.21 129.21 Note. — Add the stadia constant, 1.31 ft., to each distance reading. Survey for Contour-Lines. Contour-lines are drawn upon a map connecting points on the surface of the land having the same elevation. The vertical distances be- tween the lines may be any chosen length, as 2 feet or 5 feet, but are equal on the same map. A number on each line indicates the elevation of the ground at the points on that line which were read, and, assumedly, between them. The slope of the land is at right angles to the contour-lines, being steepest, where the lines are closest together and nearest level where they are far- thest apart. It is sometimes desirable to delineate the surface-slopes in this way as a base for representing per- manently the relation of slopes of various fields to each other and to improvements which it may be desired to establish from time to time. Taken in connection with 42 ENGINEERING FOR LAND DRAINAGE physical land conditions it becomes useful in planning drainage systems. There are two methods of survey for representing contour-lines, but the one deserving first mention is the transit and stadia method. Run a base-line through the tract, setting permanent hubs by chain and transit 1 ,000 feet apart, or less if the land is obstructed by trees and brush, and find the elevation of each. These are stations from which to make measurements with the transit and stadia rod. The base-line need not be a straight line through the entire tract, but may be de- flected to conform with the shape of the area to be examined. Set the transit over each of the stations, the height of the instrument being obtained by adding the height which the telescope stands above the station to the elevation of the station. The rodman then se- lects the point and the instrument-man reads the dis- tance to the point by the stadia, and also reads the position of the center hair upon the rod to obtain the elevation. In addition, he reads upon the limb of the transit the angle which the line makes with the base- line, or, in case the compass is used, he reads the bearing of the line by the needle. If the surface has but little slope and is uniform, but few points need be located. Side base-lines may be run out from the primary one if necessary to reach other parts of the tract. At the close of the field-work the base-line should be plotted to a convenient scale and points located on it by scale and protractor, and the elevations recorded at each point on the map. Contour-lines may then be sketched in to represent such vertical distances as may be desired. The lines will, of course, be interpolated between points on the assumption that the slope is uniform between the points recorded. The second is the level and chain method, and re- ENGINEERING TECHNIQUE 43 quires that the land first be laid off in loo-feet squares. Begin at one corner of the farm or tract whose adjacent sides are straight lines and use them as bases from which to work. Have stalces prepared about i6 inches long. Begin at the corner and measure off a base, setting a stake at each station of lOO feet, lettering the stakes A, B, C, etc., in order. Begin at the point A and measure from that point along the adjacent side in the same manner, numbering the stations i, 2, 3, etc., until the limit of the field is reached. Set a flag-pole lOO feet from the last stake at a right angle to the last line run. Begin at stake B on the base- line and run to the flag, setting stakes at each loo feet, • numbering them B i, B 2, B 3, etc. Proceed in the same manner across the entire farm until it is checked into squares of lOO feet. The lines are described by letters, and any point on the lines by the number of the stake, as B 5, D 26, etc. Before beginning the level-work, establish a bench- mark and assume a datum-plane at the initial point, or A, of the base-line. Following the lines A, B, C, etc., take levels at each of the stakes, heading the level-book pages "Levels on Line A," "Levels on Line B," etc. Two lines may be leveled at one passage. "Turning- points" should be taken on pegs, but other levels may be taken on the ground. Make a plat of the area upon a scale which should be governed by the use which is to be made of the map. One-half inch to 100 feet is a convenient scale for a farm of 160 acres. Reproduce the lines laid off in the field so that the plat will correctly represent the field on the scale adopted. (Fig. 8.) Write the elevations which are recorded in the field-book at the intersec- tions of the lines on the plat, which intersections rep- resent the position of the stakes in the field. Con- 44 ENGINEERING FOR LAND DRAINAGE v*-'' \%> ^t,." \t-* V-^ <^^ ,<'■" ^'^•y ^'*' 01 2 34 5\ 678 9 8- short cuts here and there in such a way as to make the drain less expensive and more efficient without impairing its value as a drain for the natural course. These factors in location must be determined on the ground. Submains should also follow the line of natural drain- UNDERDRAINS AND THEIR LOCATION 75 age as far as possible, and laterals should be laid in the line of greatest slope. There are exceptions to this prin- ciple, but they apply to particular cases where it is necessary to intercept soil-water which percolates through the soil from a higher level, being aided or modified in its flow by hard-pan, gravel or sand strata until its course is checked by some less pervious formation. In such cases intercepting drains laid across the slope at the proper depth are necessary to drain the bog which re- ceives such water. When drains thus laid fail to accomplish the pur- pose, it is because they have been placed above the level of the seepage water, thus permitting it to pass under them unchecked. The experimenter is apt to think it has entered the tile at one side and passed out of the other and down the slope, and to conclude that drains across the slope are ineffective. Avoid short laterals where a system can be adopted in which long parallel laterals can be used. This is a matter that relates to the economy of the work rather than to its efficiency. Every main or submain will of it- self drain the land for a certain distance on either side of it. In order to reach the mains, the short laterals must extend through the belt of land thus drained, and hence a part of each lateral will be useless except to con- duct the water to its receiving drain. The fewer junc- tions there are in a given tract, the less waste of length of laterals will there be. There are localities, however, where, on account of the contour of the land, short laterals are necessary. Locate the lines so that all the land can be thoroughly drained when the system is fully carried out. The preliminary examination will furnish the information needed regarding the character and elevation of the land, so that this can be done in a comprehensive way. 76 ENGINEERING FOR LAND DRAINAGE Systems of Drains. The various methods of arrang- ing drains for accomplishing the work required in ac- cordance with the foregoing principles are called sys- tems. The natural system consists of lines of tile laid in natural depressions that are wet and require draining more than the adjoining land (Fig. 14). They are aids to natural drainage, and complete it in localities where the adjoining higher land is naturally drained by the sv \ r-i- .-^-<\t \a f-^^ ^^Jt. "^». /* ,-''' Y^ -^ ''■^^^-^^^*3:;^ A_\ M. ^ Fig. 14. — Natural System. low depressions. Such random or occasional lines are called upon to carry the drainage of both dry and wet land, which fact is often overlooked in apportioning the sizes of tile that should be used. The natural sys- tem is the skeleton which may be developed into a more elaborate one if later found necessary. The herring-bone system consists of a main with parallel laterals joining it on each side in the manner in- dicated by the name (Fig. 15). The gridiron system consists of a series of long parallel laterals which discharge into a receiving drain from one side only (Fig. i6). It is one of the most economical and efficient systems used in treating level lands. UNDERDRAINS AND THEIR LOCATION n The grouping system (Fig. 17) takes its name from the method of collecting a number of laterals into a short main which would otherwise discharge into a ditch direct, thus making one outlet serve several drains. The double-main system is applicable to broad, flat sloughs, where it is desirable to use two lines of smaller tile instead of one large main through the center. If the land on either side has a good slope toward the slough Fig. 15. — Herring-bone System. Fig. 16. — Gridiron System. a line of seeped or boggy land may have developed at the base. A main laid on each side as an intercepting line with laterals on the slope, as shown in Fig. 18, will be effective, if the drain is placed as deep as the stratum through which the water percolates. The Elkington system was originated by Joseph Elkington of Warwickshire, England, in 1764. As now used, it consists of a few single lines of tile so located as to intercept seepage-water which percolates down a slope. In case the drain is not deep enough to fully intercept the water it is supplemented by wells which are made directly beneath the drain. These wells pene- trate the strata from which the water proceeds, and are made with an auger if the earth is firm clay, or are 7S ENGINEERING FOR LAND DRAINAGE excavated and curbed with lumber or brick if the soil is loose and unstable. In some instances the wells are filled with loose gravel. The office of such wells is to intercept the deeper currents of water. The pressure which forced the water through the soil causes it to rise in the wells and flow off through the drain which Fig. 17 — Grouping System. serves as an outlet to them (Fig. 19). This system is applicable to the drainage of bogs and springs, and is successfully used in draining irrigated land. Depth of Drains. No question relating to under- drainage is susceptible of a greater \-ariety of answers than that of the proper depth of drains. \Mth regard to depth of drainage, 4 to 4,5 j feet is called deep, 3 feet medium, and 2 to 2yi feet shallow. Advocates of deep and shallow drainage have argued their favorite theories since the time tile were first introduced. It is one of those cases in which theories are not always \'erified by practice, liic factor which prevents this being the varia- tions in the characteristics of the soil which is to be UNDERDRAINS AND THEIR LOCATION 79 drained. In order that any one theory may prove cor- rect it must apply to a soil of given characteristics. When it is said that no universal rule for depth can be safely announced, it does not follow that a safe rule Fig. i8. — Double-main System. can not be given for a locality whose soil-structure and climate are known. If an engineer's practice is con- fined to a region having the same kind of soil in all parts, he can adopt a rule of depth and safely adhere to it in Fig. 19. — Elkington System. every case perhaps, but if this region is one where the soil is open and responds readily to deep drains, he will fail if he applies the same rule to the dense clay, soils which he may encounter in other localities. It is de- 80 ENGINEERING FOR LAND DRAINAGE sirable that clay and loam soils be drained and aerated as deeply as practicable, but this operation requires that the water be removed from the surface within a reasonable time so that the sun and air can act upon the particles of soil as the water recedes. The resistance of close soils prevents this if the drains are too far dis- tant from the surface. Hence it is found that in some close, heavy soils drains at 2 to 2 >^ feet give good results where those at 4 feet fail. Many of the rich farming lands in the Middle West, with permeable soil, should be underdrained 4 feet deep, as the successful operation of many miles of drains at that depth attest. A general rule of depth then, for humid regions, is from 2^ to 4 feet, depending mainly upon the nature of the soil. In irrigated land, however, it is found that drains placed 6 or 7 feet deep accomplish the desired result, while those 4 feet deep may fail to do so. Before deciding this matter for lands with which he is not familiar, the engineer should test the soil with reference to its permeability to water. This can best be done by digging small pits where the land is wet, by means of which its physical structure and the freeness with which water seeps or percolates through it can be examined and conclusions deduced regarding the depth it will be best to place drains. In this connection it may be suggested that the drainage of dense clay soils can be materially facilitated by stirring the soil deeply, or subsoiling, thus breaking up the compact strata which are frequently found 6 to 12 inches beneath the surface. Frequency of Drains. The proper distance apart of drains is a subject that is closel>' related to their depth, since soils which respond host to shallow drains re- ciuire them placed closer together. Efficiency and econ- omy are factors in this part of the problem. If drains placed 100 feet apart gi\c satisfactory results, nothing UNDERD RAINS AND THEIR LOCATION 8 J is gained by placing them 30 feet apart, while the cost is greatly increased. On the other hand, the former distance in some cases will be so ineffective as to hardly warrant the work. Depth does not compensate for greater distance except in a limited way. As a guide to the judgment, the following distances for the kinds of land described, are suggested. They are the result of observations and experience in a wide range of condi- tions. In close, dense soils, largely clay, 30 to 40 feet; coastal plain lands composed of mixed clays with fine sand and uniform structure, 60 feet; alluvial gumbo or heavy soils, but with granular structure, 70 to 80 feet; alluvial, glacial drift and sandy loam soils, with joint clay subsoils, 100 feet; sandy lands and soils containing considerable quantities of vegetable matter and those with subsoils having a liberal supply of sandy or gravelly material, 150 to 200 feet. These suggestions apply to drains on level lands and should be considered in con- nection with depth and needed accessories referred to elsewhere. Staking out Lines. The general system having been decided upon, begin at the outlet of one of the mains to stake out the lines preparatory to construction. Suitable stakes should be prepared beforehand. These may be made of fence lath 4 feet long, i^ inches wide and H inch thick, cut in pieces 16 inches long when intended for use on land which is free from grass and heavy weeds, but otherwise 2 feet long. These are called guides, and serve to carry the station-numbers and show the location of the grade-stakes. An equal number of grade-stakes made of the same material and one foot long should be made to accompany them. Where the ditches are to be dug without much delay, stakes made of plastering lath, which are more easily carried, may be used for guides. 82 ENGINEERING FOR LAND DRAINAGE First set flags at points along the course of the pro- posed drain by which to line in the stakes. Set the first, or o stake, at a selected distance on the right of the outlet, such distance depending on the size of the ditch that is to be excavated ; drive it flush to the surface and set the guide-stake on the Hne and about 4 inches be- yond it, as shown in Fig. 20. The link chain is con- venient for measuring distances. Let the fore-chainman hold the forward handle of the chain and with it a guide- FiG. 20. — Guide-stakes and Hubs. stake in a vertical position, and let the rear-chainman with the handle of the chain over the grade-stake, and his eye -directly over it, line the fore-chainman's stake in by the flag-pole which marks a point on the line. The fore-chainman sticks the stake where directed and drops a grade-stake by it. He then pulls ahead another length and is again put into line. The rear-chainman drives the stakes and marks the guides with a heavy lead-pencil or marking-crayon, or has an assistant do so. The stakes are marked consecuti^•ely, gi\ing frac- tional distances, as 3 + 20, etc. Grade-stakes placed regularly 100 feet apart, ^\'ith fractional stakes where necessary, are ordinarily close enough together for use in constructing the drain. If the stakes are well lined "by the eye," as described, the more tedious method of lining in with an instrument is avoided and the work, for practical purposes, is just as accurate. The bear- UNDERDRAINS AND THEIR LOCATION 83 ings of the tangents, however, should be taken with the instrument. Where curves are made, intermediate stakes should be set in such a way that they can be followed and used in digging the ditch, and should be marked so as to indi- cate the number of feet from the outlet up to each stake. As for example, between Stations 5 and 6 the inter- mediates are set 20 feet apart and should be marked 5+20, 6 + 40, etc. Another point to be noted is the place where submains or branches are to join the line. The number of each branch should be marked upon its proper junction-stake. The same plan should be followed in staking drains throughout the entire system. Begin at junction-stakes and stake each line as a unit, numbering the stakes con- secutively up grade, placing upon the upper-end stake its full number and the name which is given to the line, so that a workman in looking over the system can follow the lines from either end, by schedule or map. Designation of Drains. Some orderly method of designating drains is necessary where there are many of them in a system so that notes can be kept without confusion and also correspond with the schedule and plat which should be made after the work is staked out. Mains may be designated as Main A, Main B, etc. ; sub- mains as Submain No. i of Main A; branches of a main or submain should be numbered i, 2, 3, etc., up from the o point of the main or submain. All numbering and lettering of the drains is done consecutively from the outlet toward the upper ends. Where there are two or more unit-sections with separate outlets in the same farm or plantation, they may be distinguished as Drain- age Section No. i, No. 2, etc., or by some local name, as Crooked Creek Section, Flat Woods Section, etc. Taking Levels. Levels should be taken upon each 84 ^ ^ «• So "'!?« m. m ^ rH W M W 0) pq i ^^ a ««MW o mo miommmmmmin i>-i>ododo6ooodod ovdtd>6> OtOtO^OlOtOtOtOl^Ot^Ot orsMiooorooq>ooinoq Ot^OOOMMr^NClMMMM oo>oooooooooooo PI bb b e ? o > o o o o r4 N M (s H d\ vd io in io ^ r^ M N M M o O \d vd >d !> t^ t> li J3 >d m (U + UNDERDRAINS AND THEIR LOCATION 85 grade-stake and recorded in the note-book in the man- ner shown in the accompanying specimen page of a field- book. The notes for each Une should be kept under its appropriate head or name, and all levels should be re- ferred to a common datum. The bearings of the lines should be recorded on the right-hand page of the book opposite the level-notes so that all of the data concern- ing each line will be recorded on the two pages which open opposite each other. Establishing Grade Lines. The grade upon which the tile is to be laid must be determined by measure- ments downward from the grade-stakes. The grade 10- Jll Fig. 21. — Profile of Main A. may be laid out by either one of two methods. The levels may be reduced to a profile which represents the surface-line upon such a scale that differences of tV ft. in elevation can be shown (Fig. 21 and notes). The grade may be located upon this by drawing trial lines in pencil or by using a black thread which can be shifted about until a satisfactory grade is found, and the rale from point to point determined. Another method is to select trial grade-line elevations along the line until the grade and depth at various controlling points are satis- factory. These points may then be entered and depths computed throughout the entire system without the aid 86 ENGINEERING FOR LAND DRAINAGE of profiles. This is the most expeditious method and can be used in all ordinary underdrainage work. Grade is expressed in feet per lOO ft., or in feet per mile. It is convenient to adjust the grade to an even .01 foot, as for example, .02 ft. per 100 ft. = 1.05 ft. per mile; .05 ft. per 100 ft.= 2.9 ft. per mile; 10 ft. per 100 ft. = 5.28 ft. per mile. It is also expressed as a percent, as .02% = I ft. in 5000 ft. Two columns should be added to the note-book, one for recording the elevation of the grade line at each station, and headed G L, and the other for recording the depth at each station and headed Cut. After the rate of grade has been decided upon, the amount of rise for each station must be added to the grade-elevation of the preceding one and subtracted from the surface elevation to obtain the depth of bottom from the top of the grade-stake. Examining the notes (page 84) from which the profile illustrated has been plotted, we find that a grade of .25 feet per 100 feet has been decided upon and that the outlet of the tile can begin at the bottom of a ditch whose elevation is 97.25. This subtracted from the surface-elevation at o station shows that the drain will start 2.75 feet below the surface. Add .25 to this grade-elevation and to each succeeding one, and sub- tract each from the corresponding surface-elevation. The result in each case will be the depth. These points when connected will make a straight line. When a change of grade is to be made, note the station at which it begins, and also the amount of grade, and proceed as before. The depth at which it will be desirable to make the drain will be a factor, and also the minimum grade which may be used. Drains laid on as low a grade as yi inch to 100 feet are in successful operation, and fre- quently no greater one can be obtained. If possible, UNDERDRAINS AND THEIR LOCATION 87 however, a grade of .10 foot per 100 feet should be secured, though a failure to get as much should not prevent the use of tile. A uniform grade should be used from point to point and computed by taking the difference between the elevation of two grade-line points and dividing by the length of line between the two. Where a cut is to be made through a ridge to a flat which it is desired to drain, determine the least depth of drain that should be used at the upper end, adopt a safe minimum grade, say .10 or .20 foot per lOO feet, and run down the line, subtracting the amount of grade from the grade-elevation of each station in order until the ridge is passed and the desired depth is reached, then change to a heavier grade. This is the ordinary method of grading a drain, reversed. When a submain or a lateral enters another drain it is best to have an outfall from the branch line into its main. This is commonly called a "drop," and the amount should be proportionate to the size of the tile into which the branch discharges. For example, branches joining a .6-inch main should drop .2 ft., an 8-inch, .3, a lo-inch, .4, 12-inch, .5, and 15-inch, .7. To compute the starting- point for the branch line, add the drop to the grade- elevation of the main at the junction and proceed as before. Example: At Station 4 -f 50 (see notes). Branch No. i is to have a .20 drop. The grade-line 98.35 -|- .20 = 98.55 = elevation of grade-line at the outlet of the branch. This should be transferred to the notes of Branch No. i and used as the initial point for computing the grade of that line. Construction Figures. There are two methods of indicating the depths of cut at the several stakes for the use of the workman. They may be marked with a lead-pencil direct upon the guide-stakes, noting also 88 ENGINEERING FOR LAND DRAINAGE the points at which there is a change of grade. The workman then sets his guide-line and grades the ditch in accordance with the marks he finds upon the stakes. The more convenient and in many respects the better way is to prepare a tabulated statement in a small memorandum-book of pocket size which the workman or superintendent can use and keep for reference. This memorandum should give the depth at each stake, the grade, and size of tile to be used. The following form will suggest to the engineer the manner of preparing the working figures: DEPTHS OF DRAINS ON LIMESTONE FIELD Main A Branch No. i Stake Depth Ft. In. Stake Depth Ft. In. 3 I Grade 2-in. per 100 ft. 4 3 7 3-in. drop I 2 SH 8-in. tile 3 4 Grade 3-in. per 100 ft. 3 3 4M I 2 10 S-in. tile 3 4 2 a 9H 4 3 7 Br. No. I enters 4 + 50 2 II in pond 3 3 3% 5 3 I 4 3 iH S + 6o 2 IllA* Br. No. 2 enters 4 + 6o 2 II End 6 2 10 * Grade 2}4 in. per 100 ft. The Map. A complete map should be made after the field measurements have. been finished. The value of full notes and sketches of the several divisions will now be appreciated, for from them a good working map for use in construction in connection with the specifi- cations, as well as a permanent record of the drains, UNDERDRAINS AND THEIR LOCATION 89 can be made. The map should show the location of each drain, its outlet or its junction with another line, its total length, which should be placed at the end, the number and size of the tile required, the location of all surface-inlets, silt-basins, etc. It is also well to record the grade of the drains from point to point, and the sur- face elevations at various representative places through- out the tract. It should be remembered that the map is made to record information relating to the drainage of the tract represented in a comprehensive and compact form. Figs. 22 and 23 show sections of a map each delineating a TABLE I Decimals of a Foot Reduced to Inches Foot Ins. Foot Ins. Foot Ins. Foot Ins. Foot Ins. .0104 Va .2188 2^ .4271 tVa •6354 7% .8438 loYs .0208 M .2292 M •4375 M .6458 M •8542 M .0313 Va .2396 y% •4479 y% •6563 % .8646 % .0417 y^ .2500 3 •4583 y^ .6667 8 .8750 Yi .0521 % .2604 Va .4688 % .6771 M .8854 Ys .0623 Vi .2708 M .4792 % .6875 M .8958 Ya .0729 Vi .2813 % .4896 % .6979 % .9063 Ys .0833 I .2917 Vi .5000 6 .7083 y, .9167 II .0938 M .3021 y% •5104 H .7188 % •9271 Ys .1042 M •3125 M .5208 M .7292 Yi •9375 M .1146 y% .3229 Va •5313 % •7396 Yb •9479 Ys .1250 Vi .3333 4 •5417 y, •7500 9 •9583 y2 .1354 Ys •3438 Vi •5521 % .7604 Yb .9688 Ys .1458 H •3542 M •5625 M .7708 M •9792 M .1563 Vs .3646 y% •5729 % •7813 % .9896 Ys .1667 2 .3750 Vi •5833 7 .7917 Yi 1. 00 12 .1771 Vs •3854 % •5938 % .8021 Y% .1875 H •3958 M .6042 M .8125 Ya .1979 Vs .4063 Vi .6146 % .8229 Ya .2083 Yi .4167 5 .6250 ^ •8333 10 90 ENGINEERING FOR LAND DRAINAGE Fig. 22. — Section of Farm Drainage Map, No. i. From files of Drainage Investigations U. S. Dept. of Agriculture. UNDERDRAINS AND THEIR LOCATION 91 Fig. 23. — Section of Farm Drainage Map, No. 2. From files of Drainage Investigations U. S. Dept. of Agriculture. 92 ENGINEERING FOR LAND ' DRAINAGE different system on a single plantation. The entire map has a title and explanatory notes such as are de- scribed in Chapter III. The figures also illustrate the use of the different systems or arrangements of drains to meet the conditions of the land. Reduction Table. For convenience in reducing the decimal expressed in the cut, or depth, column of the notes to inches and fractions of an inch, which will usually be demanded by workmen when digging the ditches, a table is here given. In all engineering com- putations it is desirable to use the decimal scale, but the engineer will soon learn the equivalents of decimals of a foot in inches and fractions, so that he can write them without referring to the table. Reductions to the nearest M inch are sufficiently close for use in con- structing ditches. (See Table I, page 89.) CHAPTER VII FLOW IN UNDERDRAINS That the engineer may determine the size and num- ber of drains which shall be adequate for any system of drainage, it is necessary that he understand and be able to apply the principles governing flow of water. Elaborate experiments and painstaking investigations have been made by eminent hydraulicians on the flow of water through pipes and channels, but only such re- sults of their work as have a bearing upon drainage problems need be discussed here. Effect of Gravity. It should be borne in mind that gravity is the sole cause of flow of water, except when mechanical force is used. Gravity causes unsupported bodies to fall vertically, a ball to roll down an incline, and water to flow down hill or through an inclined pipe. The formula used to express the theoretical velocity due to gravity in the case of falling bodies is: V = V 2 gh (i) where V = velocity in feet per second, g = accelerating force of gravity, = 32.2, h = space through which the body falls. It has been found by experiment that a body in vacuum at the level of the sea passes through a space of 16.1 feet during the first second, and at the end of that time has acquired a velocity of 32.2 feet. The velocity at the end of each succeeding second of time is 32.2 feet greater than it was at the end of the preceding second. This is called the accelerating force of gravity, and is desig- 93 94 ENGINEERING FOR LAND DRAINAGE nated in the formula by g. The following table shows at a glance the relation of time, space, velocity and accelerating force of gravity to a falling body during the first five seconds. TABLE II Falling Bodies During First Five Seconds I Sec. 2 Sec. 3 Sec. 4 Sec. S Sec. Space = h 16.I 32.2 32.2 64.4 64.4 32.2 144.9 96.6 32.2 32.2 402.5 Velocity = v Accelerating force = g . 32.2 Water flowing down an inclined surface would follow the same law were it not for resistances of various kinds which constantly act upon the particles of water as they descend and check their velocity, producing a more or less uniform flow. Were this not the case our ponds and lakes would soon empty themselves, and brooks and rivers would at times become dangerous torrents. Velocity Formulas for Flow of Water. Many eminent experimenters have applied themselves industriously to the task of ascertaining the value of these retarding forces, and by the introduction of other factors into the gravity formula so modifying it that it shall be a correct expres- sion for the flow of water under known conditions of chan- nel, and thus make it of use in practical affairs. Simple as the problem may seem at first, it has occupied the time and thought of these hydraulicians for many years, and they are justly noted for their researches in this department of practical science. The results of their labors are a number of velocity formulas which bear the names of those who developed them and which have been found to be reasonably correct for the conditions under which the researches were conducted. Thus we have the formulas of Prony, Du Buat, Weisbach, FLOW IN UNDERDRAINS 95 Bazin, D'Aubuison, Beardmore, Chezy, Darcy, Poncelet, Neville, Eytelwein, Kutter and others, all of which have been used by engineers with more or less con- fidence. Such formulas are essential in the work of engineers, and their value depends upon the nearness to which the results they give approach the actual measured velocity of flow. When we consider the great variety of conditions which affect the flow of water we can easily appreciate the difficulty of de- veloping a formula of general application. When the flow of water through pipes is considered, the resistances to gravity are, first, resistance to the entrance of water into the pipe; second, the resistance offered by the walls of the pipe with which the water comes in contact. The first will vary with the kind of opening through which the water enters, the second with the roughness of the walls of the pipe, its length and diameter, and the number and size of bends. In the case of drain-tile laid in the soil, water enters the pipe through the spaces between the ends of the tiles, en- countering a resistance dependent upon the size and roughness of the opening. The flow through the pipe is retarded by the roughness of the walls, bad joints, bends, the discharge from laterals, and sediment, if any exists. The form of Weisbach's formula is such that the corrections which must be applied to the gravity for- mula so that it will express the velocity of flow in pipes are readily seen: V 2 gh (2) V 1 where " e = coefficient of resistance to entrance of water into pipe, c = coefficient of friction of pipe, 1 = length in feet, d = diameter of pipe in feet 96 ENGINEERING FOR LAND DRAINAGE The numerator of the second member of the equation we recognize as the theoretical velocity of falling bodies (Formula i); the denominator represents the resistances to flow through the pipe. We thus have the formula for falling bodies so modified that it will express the velocity of water in pipes. There are other formulas, equally if not more accu- rate, which possess the very desirable excellence of greater simplicity. Beardmore's is one of the more simple formulas: V = ioo\/r s (3) where ' r = hydraulic mean depth, or hydraulic radius, _ area of waterway _ a ^ wet perimeter p 5 = sine of slope, _ head, or fa ll, i n feet _, h length of pipe 1 Written in full, the formula is: I cross sectional area head V — 100-^ ^gj perimeter length of pipe' all dimensions being in feet. The Chezy formula has the same form, but is more elastic : V = c\/r s (4) This permits the substitution of different values for c, expressing variations in the resistance, making the formula adaptable to a wider range of conditions than when a fixed value is used as in Beardmore's formula. The foregoing expressions are given to show the deriva- tion of velocity formulas which are used by engineers in computing the flow of water through continuous pipes, sewers and conduits of various kinds when the FLOW IN UNDERDRAINS 97 head of water is known and the pipes come within rea- sonable Hmits of perfection in workmanship. When the velocity is found, the discharge is obtained by multiply- ing the area of the column, or stream, of water expressed in square feet by the velocity in feet per second. The result will be the discharge in cubic feet per second. This is expressed by forqiula as follows: Q = a V, (5) where Q = quantity in cubic feet per second, a = area of column of flowing water in square feet, V = velocity determined by formula. Then the relation between discharge, area, and veloc- ity are: v = 2 a a = 2 V Then for discharge, Beardmore's formula becomes: Q = 100 aN/r s (6) and Chezy's, Q = a cVtI (7) This is sufficient discussion to direct attention to the several factors that must be recognized in constructing a formula that will correctly represent the flow of water in pipes. Formulas for Flow in Tile Drains and Their Use. Flow through a pipe is not uniform in different parts of its diameter. Measurements show that the velocity is least at the circumference and that it increases toward the center. Concentric rings within the pipe have ap- proximately equal velocity, but such rings are not always circles, showing that in the best constructed and laid pipes there are internal eddies which disturb the regu- 98 ENGINEERING FOR LAND DRAINAGE larity of flow. Experiments also establish the fact that in pipes, especially tile drains and sewers, velocity is not uniform in different lengths of a drain which has the same diameter and gradient. Formulas represent the mean velocity of flow, that is, a velocity which multiplied by the area of the pipe will correctly express the rate of discharge. The elements which produce and control the flow are the gradient or head, the degree of rough- ness of the walls of the conduit and its cross-sec- tional area. Formulas express the law of flow when these factors are known and the water is supplied to the pipe. The application of a velocity formula to tile drains in such a way as to be useful in the design of under-drainage systems, is subject to some difficulties which will be here discussed. A tile drain is a continuous pipe made up of sections one, two, or three feet long, with small spaces between them through which water enters. W'hen the soil surrounding the pipe is saturated, water enters all parts of the joint along the entire line, pressing into the pipe with a weight the amount of which depends upon the openness of the soil and consequent freeness with which water passes through it. When the soil is satu- rated, with occasionally free water on top, a condition which occurs when drains are called upon to perform their maximum duty, water flows through the drain with a velocity due not only to the slope of the drain, but to the head added by the soil water above the drain, equal to the weight of free water less the resistance offered by the intervening particles of earth. The practical effectiveness of this head has been proven where tile drains have been laid in open soils upon a level gradient but with free outlet. A liberal discharge takes place with no head to produce flow except the water above tlie tile. Soil water head diminishes in FLOW IN UNDERDRAINS 99 proportion to the closeness of the soil, becoming nearly zero in tight clay soils. " Another hydraulic condition peculiar to tile drains Is that in any extended system, a series of submains and laterals furnish a flow to the main drains through pipes which usually have a greater fall than the main, or in any event have a drop at the point of discharge so that the entire lateral system occupies a higher level than the main drain and when full and in operation adds to the effective head of the main and accelerates its flow. The effect of such a condition is seen where the lateral system on one side of a main occupies a higher level, and has drains with greater slope than the oppo- site corresponding side. The discharge from the low level drains is held back until the flush flow from the drains with heavier gradient has passed. Another instance of not infrequent occurrence, is that of a large main tile laid upon a light grade to serve as an outlet for a large number of laterals. When operating under ' conditions of maximum flow the water "shoots" from the tile with much greater velocity than that due to slope upon which it is laid, showing that it derives an added head from the laterals which discharge into it. A tile drain under certain conditions of saturated soil which surrounds it may become a mere conduit through which water may be forced by a supply which is brought to it from a higher level. The so-called "raised outlets," quite commonly used in the earlier tile drain practice, depend for their operation upon the ability of a drain passing through a saturated soil to with- stand the pressure of water flowing under a considerable head. The foregoing conditions peculiar to tile drains make it impracticable to apply the accepted formulas for velocity in pipes to the design of tile drainage systems lOO ENGINEERING FOR LAND DRAINAGE without certain modifications which will take those conditions into account. Many rules and formulas which have been prepared by engineers for this work, since the tile drainage has come into prominent notice, have been discarded by practical drainers because they failed to give the results that were obtained in actual practice. The formulas were not sufficiently flexible to meet the hydraulic conditions under which drains operate. Another condition modifying flow in tile drains is the roughness and irregular alignment of the conduit as commonly constructed. These retarding forces must be represented in the formula by appropriate variable factors if reliance is to be placed upon the results it gives. The perfection of workmanship in constructing the drain has a greater effect on flow than is usually suspected. Careful measurements made by students of an Iowa State College, Ames, Iowa,* demonstrated that certain large tile well laid discharged 8 per cent more than the same size and kind of pipe which was laid in a more irregular manner, both, however, being commonly accepted as well-constructed drains. This confirms what has been found true in practical work as to the effect which the condition of the conduit has upon its discharge, and emphasizes forcibly the fact that good workmanship even to the extent of o\erexactness will materially increase the carrying capacity of a drain. European engineers, particularly those of France and Germany, have examined this phase of the subject quite fully in an attempt to develop a correct expression for flow in tile drains. Mr. L. Faure, General Inspector of Agricultural Improvements of France and author of "Faure's Drainage," in treating this subject says: "It is quite apparent that to express the flow of water * Vol. 4, No. 5, Bulletin Iowa State College Experiment Station. FLOW IN UNDERDRAINS lOI in tile, we sliould not take formulas that are applicable to ordinary conduits for tiles present numerous pecu- liarities." These he proceeds to note and further says, "During the early years which followed the introduction of drainage by tiles, engineers attempted to determine the diameter of drains by formulas used for the flow of water in ordinary conduits. As for example, Leclerc, in his 'Treatise on Drainage,' and Lafifineur, in his ' Practical Guide to the Agricultural Engineer, ' adopted for this calculation the Darcy f onnula.' ' After citing two formulas which for a time were favored by engineers, he says, "These formulas have been abandoned by the majority of engineers who now prefer the one proposed by Vincent, and which has been adopted by the General Commission of Silesia as well as by Perels, Gerhardt, and more recently by Nielsen." The expression referred to has the form of the Poncelet formulai which the author has adapted for use in the design of tile drainage systems: V? ^^ (8) + 54d in which V = mean velocity in feet per second. d = diameter of tile in feet. h = head, or difference in elevation in feet between the extremities of the drain which is considered. I = length of drain in feet, a = area of tile in sq. feet. Q = discharge in cubic feet per second. *m = coefficient dependent upon diameter of the tile. *The original expression gives m = 48 for all diameters. It has been found that a given roughness of surface bears a greater proportion to the whole area of surface in a small pipe than in a large one. Hence m has different values for tiles of different diameters. The values given in the table coincide with those determined for drain tile. I02 ENGINEERING FOR LAND DRAINAGE Values for m DIAMETER OF TILE Inches Feet m s .42 34 6 50 36 8 .67 40 9 75 43 10 £3 44 12 1 .00 45 i6 I 33 47 i8 I 50 50 24 2.00 54 30 - 50 57 36 3 00 60 42 3 50 61 48 4.00 64 This formula applies to a well laid, straight drain, running full on a uniform gradient. It should be under- stood that h in the formula applies to head which is distributed so as to produce an even grade throughout the line. The values of the coefficient m represent the retarding effects of frictional resistance which is greater for small pipes than for large. For irregular shaped and badly laid tile, these values should be decreased as the judgment of the engineer may dictate. Modifications of the Formula. The effective head under which a drain operates when discharging its maximum volume is the difference in elevation between the extremities of the section of the drain, which is under consideration V plus the weight of water in the soil above the drain. The latter is variable, depending upon the openness of the soil and the consequent freeness with which water percolates through it. The frictional re- sistance occasioned by the soil particles and by the joints of the drain absorb a large part and in many cases nearly all of the outside head. Nevertheless it is a tangible FLOW IN UNDERDRAINS I03 and important factor in the discharge of drains, for it has been found that drains under conditions of maximum flow discharge a greater volume than is indicated by the ordinary formula. A factor may be introduced in the formula to represent the additional head, which would be a depth of water equal to a part of the depth of the soil above the drain. Representing this depth as k, we may add to h some fractional part of k, as .5 or .3, to obtain the total head which should be used. The formula would then become: -^"i (I' + 'Sk) (9) + S4d The length of the drain to which the formula should ' be applied should be a representative part which is laid on the least grade. The value to be given to k is neces- sarily dependent upon the character of the soil. Its value would be large where surface inlets are introduced along the line. Another factor which has even a greater effect upon the velocity of flow in a main drain, and in some cases requires a second modification of the formula, is the number of submains which discharge into it and the fall they have compared with that of the main. If they have a grade about the same as the main or receiving drain, no additional velocity will be imparted. But if the drains which feed it have a greater grade or are laid upon a higher level, the velocity of flow will be increased by reason of the head of such drains which connect directly with the main. The branches comprising a system of drains when full of water may be regarded as a series of small reservoirs which are connected with the main drain and by their pressure add to the velocity of its flow. The head provided by such submains, or by the upper part of the main when it has a large fall, converts 104 ENGINEERING FOR LAND DRAINAGE the lower roach of the drain into a pipe which flows under pressure. Under such conditions soil water is prevented from direct entrance into the main, unless it is of ample size, until the flood supply of field drainage water is reduced. The head of a main with submains which have a greater rate of fall than the main would be h plus the average additional head supplied by the submains. Let b represent the sum of the differences between the head of the main and that of the several submains and n the number of submains; then the total head will be: h H , in which n h = head of main, b = sum of amounts in which head of submains exceeds that of main, n = number of submains. The formula thus modified becomes: ,JlM) 1 + 544 '"> This increase of head should not be computed for the laterals which discharge into submains. The formula should be restricted to mains which have sub- mains not less than six inches in diameter and connected with that section of the main drain whose capacity is being computed. Where extended systems of tile are used which require large and costly mains and submains, all of the factors which have been mentioned in the fore- going discussion should be given tlieir proper place and weight as nearly as practicable. A close adherence by engineers in tlie design of drainage systems to hydraulic formulas, which have been found satisfactory for other purposes, has led to badly balanced designs and the FLOW IN UNDERDRAINS 105 adoption of sizes of tile that have discouraged owners in the construction of drainage works. In some cases the plans of the engineer have been modified in the interest of economy but the changes have not always been in accord with sound practice. There is much room for the ex- ercise of a trained judgment in the application and use of velocity formulas in drainage design. It is a matter of common observation that a tile drain of given size is more efficient under one condition than the same size of drain is under other conditions due to the causes which have been referred to in the foregoing discussions of the subject. Examples : FORMULA (8) I. What is the velocity of flow at the outlet of a line of 12-iiich tile running full, 1500 ft. long, laid on a grade of .20 ft. (2}4 inches) per 100 ft.? d = I h= 3' 1 = 1500 m = 45 V = 45.C 1 ''^^ = 45V.00193 = 1.91 \ 1554 2. For an 18-inch tile m = 50 ; v = 2.65 3. For a 24-inch tile m =54; v = 3.29 4. What is the velocity of flow in an 8-inch tile running full, laid on a grade of .10 ft. (i^ inches) per 100 ft., length 1600 ft.? d = .666 h = 1.6 1 = 1600 m = 40 54d = 36 = 40 I -^^^ X '-^ = 40 V":^^66 \ 1636 FORMULA (9) 5. Taking the data given in example i, but adding the condition that the drain is laid in a porous soil, such as peat-muck or open joint clay with 3 ft. of soil above the top of the tile, what will be the I06 ENGINEERING FOR LAND DRAINAGE maximum velocity when the soil is saturated along the entire length of the drain 7 h = 3 + -Sk = 4 -5 | iX4-5 45 V.00289 = 2.40 FORMULA (10) 6. An 18-inch main drain 2000 ft. long laid on a grade of .20 ft. per 100 ft. has 4 submains discharging at various points along its length. What will be the velocity of the main at the outlet, the submains being described as follows: No. 1 1000 ft. long, grade .30 ft. per 100 No. 2 1200 " " " .25 " " " No. 3 600 " " " .50 " " " No. 4 800 " " " .40 " " " No. I 1000 ft. on grade of main 2.0 ft. submain 3.0 dif. ft. i.o No. 2 1200 " " " " " 2.4 " " 3.0 " " .6 No. 3 600 " " " " " 1.2 " " 3.0 " " 1.8 No. 4 800 " " 1.6 " " 2.20 " " 1.6 Total 5.0 Thus h = 4.0, b = 5.0, n = 4 ; substituting in formula, 4.0 -\ — ^ = 5.0 = actual head^f main. 4 d= 1.5 h = 5.0 1 = 2000 m = 50 S4d = 81 = 50^ ^^Ip " S0V.0036 = 3.0 CHAPTER VIII THE RUNOFF FROM UNDERDRAINED AREAS To determine the duty of a drain, or the quantity of water it will be required to discharge in a given time, is more difficult than to develop a formula which will express its carrying capacity. It is the office of a main drain to remove the water brought to it either by perco- lation through the soil, by a series of laterals, by such surface-inlets as may be provided, or by all these com- bined. The measure of runoff which seems most rational, and which is now employed by drainage engineers, is a certain depth of water, in inches, which must be re- moved in 24 hours from the entire watershed to be drained. This amount is called the drainage coefficient of that area. Rainfall is measured and recorded in inches of depth; the fluctuations of the soil water-table and the amount of evaporation from the surface are measured by the same unit; the amount of water which is required to wet or irrigate a dry soil sufficiently to nourish vegetation is expressed in inches of depth; all of which suggest that the depth unit is the one most natural and convenient to use in drainage computations. The formula for determining the number of acres a drain with a known discharge will serve is: A = § („) in which A = Acres which wUl be drained Q = volume drain will discharge in sec.-ft. c = quantity corresponding to drainage coefficient, taken from Table III. 107 I08 ENGINEERING FOR LAND DRAINAGE To use this formula, divide the value of Q found by Formula 8, or a modification of it, by the number taken from Table III, which expresses the quantity of rainfall per acre or per square mile which it is desired to remove per second. The result will be the number of acres for which the drain will provide outlet. The coefificient should be selected from the table after consideration of locality, climate and rainfall. These will be dis- cussed later on. Drainage Coefficient of Underdrained Soils. No sub- ject relating to drainage merits more careful considera- tion by the engineer than this. Tile-drainage systems were formerly employed only in draining fields of limited area, a system with a main 8 inches in diameter being looked upon as a large one. Now district systems often require main drains of pipe 36 inches in diameter. The determination of the economical size of the main, submains and laterals for such systems becomes a much more intricate problem than for the large field or me- dium-sized farm. The conditions which affect the runoff from under- drained areas, be they large or small, are different in some respects from those attending the drainage of land by surface-ditches and natural watercourses. Underdrained soil is in a condition to receive water at every point where it falls, storing it beneath the surface instead of upon it, and later distributing the surplus to drains in its vicinity which are perfectly adapted to its removal. It will hold more water than one which is not drained, and in that way serves as a reservoir which regulates the flow to the mains, thus making their discharge more uniform. Such drainage prevents the massing or congestion of water on the surface which is so common on lands where open channels are depended upon. For these reasons the drainage co- THE RUNOFF FROM UNDERDRAINED AREAS IOC) efficient for tile-drained lands is not as large as it is for those from which the runoff is removed by open channels, notwithstanding that tile-drained land is dried more quickly than that drained by open ditches. Conditions Governing Runofif. The amount of run- off which should be provided for is governed by the following conditions: First, by the amount of rainfall in 24- and 48-hour periods. The maximum monthly precipitation is usually a fair indication of large daily storms, but this is not always the case. Second, by the season of the year when the large pre- cipitation occurs. If it occurs during the winter or spring months, the runoff is larger than if the same amount falls during the summer months when evap- oration and transpiration from plants is great. Third, by the openness of the soil and the consequent quickness with which it will absorb the rainfall. An open soil will permit the water to reach the drains more rapidly than will a dense clay soil, and hence will require tiles of greater capacity, but the lines may be placed further apart. The very quick and rapid removal of soil-water is not desirable in the drainage of farm land. The object should be to remove the surface-water quite quickly and secure a gradual movement of water through the soil into the drains. This movement is beneficial since fer- tilizing materials at the surface, both solid and gaseous, are lodged with the soil particles as the water percolates among them, and the air follows with its disintegrating effect upon the unweathered earth. For these reasons, sufficient drainage is better than too much. The Drainage Coefficient a Variable. It is evident that the drainage coefficient for underdrained areas is a no ENGINEERING FOR LAND DRAINAGE variable, having different values for different sections and climates. The government of the province of Silesia, Prussia, and also the French government, both of which exercise more or less authority in land-drainage operations, recommend for tile-drains a coefficient of .22 inch for level land and .29 inch for broken land. In Southern Germany, where experiments are conducted in draining moorland, water has been found flowing from tile-drain systems at the rate of yi. inch in 24 hours. Haarlem Lake, Holland, with an area of 43,000 acres, is drained by pumps which remove at times Yi of an inch in 24 hours. The annual rainfall ranges from 27 to 40 inches, the latter being the extreme. For the fens of Eastern England, whose drainage is dependent upon the fluctua- tions of the tide or upon the operation of pumps, a runoff of yi inch is now agreed upon by English engineers as the proper amount, and pump stations are designed upon that basis. The soil is absorptive, the main ditches have a fall of but a few inches per mile, and the annual rainfall is usually 22, rarely exceeding 27 inches. In Western England, where the annual precipitation reaches 50 inches, provision is made for removing 3 4 inch in 24 hours. The field drainage of Haarlem Lake and of the fens is principally accomplished by frequent open ditches which lead directly to the main ditches from which the water is pumped, but are comparable in some respects to tile-drained lands. The successful operation of drain- age by pumps requires large reservoir capacity in the ditch system, in which the water is held until the pumps can remove it. From one-twentieth to one-thirtieth of the surface is usually occupied by ditches. It is only in recent years that any attempt has been made in the LTnilcd States to proportion the size of THE RUNOFF FROM UNDERDRAl>fEt) AREAS III main tile-drains by any method having a general appli- cation to a given section of country. The practice commonly followed has been to lay such sizes of drains as the judgment of the landowner or engineer might dictate, and replace them later with larger ones should they prove too small. But it has not infrequently been found that in such revision much larger tile than were necessary have been used in the attempt to avoid re- peating the first error. Examinations in Illinois and Iowa. In order to as- certain the capacity of tile-drains which are giving good service in the drained areas of Illinois and Iowa, and to arrive at a coefficient which will be adapted to similar lands. Drainage Investigations, of the U. S. Dept. of Agriculture, directed that a .large number of systems be examined. The report of that work shows some interesting and valuable facts regarding the opera- tion of large tile-drainage systems.* Method employed. The capacity of the tile outlet of each system was computed by Formula 8, using the lower 1000 feet of length, the grade upon which that length was laid, and the diameter of the tile as quan- tities for substitution. The drainage coefficient shown is the depth of water, in inches, which would be removed in 24 hours from the entire area which was served by the main drain. The measure of thoroughness with which the lands were drained was ascertained from the farmers who owned and cultivated them. Efficiency. The soil of the entire area is a black open loam with joint clay subsoil, and is noted for its ready response to underdrains. Lateral drains are placed from 100 to 250 feet apart for thorough field drainage. * Report of Drainage Investigations, U. S. Dept. of Agriculture, upon Runoff from drained Areas in Illinois and Iowa, 1908, by L. L. Hidinger. ii: ENGINEERING FOR LAND DRAINAGE RECORD NO. 1 Size of Tile Outlets in Livingston and Iroquois Counties, Illinois System Dia. of Tile, Ins. Grade of Drain, Percent Acres Drained Drainage Coefficient, Ins. A 24 .12 1040 .16 B 18 .07 400 .16 C IS .05 400 .08 D 18 .10 480 .16 E 20 •OS 1280 .053 F 22 .09 1020 .114 G 18 •17 680 •143 Systems A and B. Land formerly a level marsh with sandy subsoil; drains give satisfactory service. System C. Drain much too small; will be removed and a larger tile used. System D. Land somewhat rolling; tile has been in service a number of years, but is considered too small for that locality. System E. This district is three miles long, the main drain being laid in the bottom of a surface-ditch which is maintained and serves as an overflow channel; the subsoil contains sand and gravel, the drain is considered satisfactory, though some of the landowners maintain that a larger one would be better. System F. Drainage satisfactory. System G. Drainage should be aided by shallow open trenches extended into ponds that collect water faster than it can be removed by the drain ; the tile unaided by an overflow-ditch is not large enough. We may conclude that a coefficient of .16 inch, or about }i inch, proves sufficient in some of these lands, par- ticularly those that are level and have open soils, but that in other cases the main tile-drain should have a THE RUNOFF FROM UNDERDRAINED AREAS 113 shallow overflow-ditch to aid in carrying more than usual precipitation. The inference is that % inch will be ample for reasonably level lands of this class. RECORD NO. 2 Size of Tile Outlets in Boone County, Iowa No. of Drain Dia. of Tile, Ins. Grade of Drain Percent Acres Drained Drainage Coefficient Ins. 3 22 •05 560 •17 II 24 •13 1240 .14 15 12 .10 200 .14 16 28 .08 940 .22 18 22 •31 1040 .21 23 12 .12 150 .20 26 18 .20 500 .22 27 18 •50 600 .27 Efficiency. The land in this county is more undu- lating or rolling than that represented by the Illinois record. Drain No. 3. This area is long and narrow, the main tile occupying the course of the open channel which formerly drained the district; drainage is considered satisfactory. Drain No. 11. Tile considered too small; the plan of the engineer shows that an overflow-channel was to have been made and maintained, but this has not been done; land is rolling to such a degree that water runs quite quickly into ponds and depressions. Drain No. 15. Land rolling and interior drainage not completed; overflow ditch recommended as a part of the plan, but not made; drainage not satisfactory. Drain No. 16.. A part of the land is composed of peat, or muck, underlaid with clay, the balance black loam; 4rain is large enough. 114 ENGINEERING FOR LAND DRAINAGE Drain No. i8. This district is four miles long, but narrow; drain satisfactory. Drain No. 23. Size of drain ample. Drain No. 26. Drain is considered ample though lateral systems have not been constructed. The results show that a drainage coefficient of Vj or Ve inch in connection with shallow overflow-ditches will give satisfactory, drainage, and that V4 inch will gener- ally prove satisfactory, except where steep sloping land adjoining the ditches precipitates a surface-fiow of water along the course of the drain. Rainfall in Illinois and Iowa. The rain<'all of these sections should be studied in connection with drainage records in order to apply the data to other sections. RECORD NO. 3 Monthly Rainfall in Livingston County, Illinois. 1398-1907 s >< 1 rt S u a < < 0. u > 1 u a "3 No. Times Rain Exceeded I In. in 24 Houts Ins. Ins. Ins. Ins. Ins. Ins. Ins. Ins. Ins. Ins. Ins. I Ins. Ins. 1898 3.80 2.07 6.64 2-95 6.12 3.79 0.29 3-35 4.86 4.42 2.50; 1.26 42.05 14 1899 0.80 2.13 1.76 0.70 2.08 S-07 4-73 2.29 2.57 2.31 2.03 2.06 28.53 7 1900 1.76 4-50 2.87 1.09 3-72 2.99 4.49 5-03 1.99 1.69 3-35 0.42 33.90 No Record 1901 1.60 1.03 3-17 0.50 0.93 3.71 2.00 1.67 2.05 1.44 I.I4,3.S4 22.78 No Record 1902 0.44 1-43 3.82 2.10 ,S.72 11-53 7-52 3-62 S.36 2.09 311,1.49 48.23 No Record 1903 0.80 3.23 2.54 4.94 4.36 1-39 6-35 2.60 3.62 2.76 1.06:1.98 35.63 10 1904 392 1.84 5-73 3.63 2.67 1-95 S-37 2-45 S-79 0.17 0.06 a. 14 35-72 8 '905 1.80 1.89 2.17 3-45 6.33 1.70 1.78 1.82 2.26 2-53 2.a6 1.71 29.70 7 1906 3.07 1.78 3.28 2.18 1.77 a-3S 2.39 0.80 3-S6 1.61 2.58 2.62 27-99 5 1907 5.62 0.15 2.74 3-09 3.28 3-00 5.60 ♦•47 4-59 0.6: 3-05 No Record Occasional rains araouiUini; to 1.75 and even a.jo inches occur in twenty-four hour period!. THE RUNOFF FROM UNDERDRAINED AREAS "5 RECORD NO. 4 Monthly Rainfall in Union County, Iowa. 1872-1908 t— » 13 u a < & S V ei) - < a 4-J > u Q c 1 i8vi Ins. Ins. 1.99 Ins. Ins. Ins. Ins. 3.46 Ins. 4.11 Ins. 4.90 Ins. 1. 17 Ins. 2.20 Ins. 3.70 Ins. Ins. 1873 0.5s 0.90 2.65 4.83 6-35 4.00 4-45 2.65 2.80 3.10 I.I5 0.75 34-l8 1873 0.85 0.79 0.60 3.10 3-55 3-75 3-43 0.60 2.95 1.25 0.30 2.15 23.24 1874 0.22 o,r6 0.17 3-15 2.45 8.55 6.15 I.2S 9-50 0.65 2.50 1. 10 35.85 1875 0.50 1.70 1.95 1. 00 1.80 8.55 9.70 2-95 8.35 2.00 0.20 2.70 41.40 1876 1. 15 0.70 2.90 S-20 3-20 6.40 3.15 2.10 7-25 1.95 2.25 0.25 36.50 1877 i-iS 0.S5 1-75 4-30 S-50 6.25 2.50 3-55 1.85 4.00 1.46 1.80 33.66 1878 0.80 0.70 3-35 1-53 4-30 8.30 S.II 3.10 2.16 2.05 0.30 0.72 32.42 1879 0.80 0.85 0.55 2.0s 1880-93 . . 1894 ....1 2.15 0.96 0.12 3.51 3-53 0.58 1. 10 1895 0.40 0.52 0.76 4.63 3-04 6.58 3-54 6.45 3.06 0.50 I.I3 2.00 32.61 1896 o.so 1.09 2.34 3.67 6.85 3.00 9.10 7.15 4.94 3.93 1.06 0.53 44-16 1897 i-iS 1.70 5.61 8.01 2.19 4-57 1.89 1.33 2.72 1. 12 0.34 2.33 32.96 1898 1.75 I-5I 2.07 2.38 4.25 5.76 2.67, 0.59 3.29 1.03 2.24 0.69 29-23 1899 0.40 0.50 1-25 2.25 6.76 4-73 6-33 S.14 0.50 1.53 0.45 1.31 31.15 1900 0.23 I-5I 2.52 3-39 4.42 2.02 5.67 4.59 596 6.90 I. II 0.25 38.57 1901 0.76 I.XO 3-19 3.21 2.90 S-05 4.42 0.44 3-55 2.82 I.I7 1. 00 29.62 1902 1.30 0.40 0.71 1.85 V-3I 4.88 8.67 5.80 7-32 4-32 1.90 2.30 46.76 1903 T. 0.96 0.71 1.45 U.90 2.97 2.83 12.34 3.38 1.96 0.88 0.20 39-58 1904 2.02 0.15 2.95 5-61 4.20 2-55 4.22 4.66 2.80 0.85 T. 2.30 32-31 190S 1-35 1-35 1.87 4.17 4.76 6.12 2.84 4.67 5-27 3.66 3.12 0.2s 39.43 1906 0.40 1,00 2.21 4.25 2.97 2. II 1.76 363 2.43 1.48 1.90 1.85 25.99 J907 1-25 0.78 1-95 1.92 2.26 5.75 5-96 5.13 2-35 1.99 1-35 1.24 31-9^ 1908 0.60 1.48 0.97 1.64 1.99 1.23 3.33 8.69 5-90 3.52 5-21 0.76 6.55 2.62 2.02 1.35 0.35 1.24 37-95 Means . . . 0.82 4-75 4.93 4.48 1 3-8o 3.82 34.10 Il6 ENGINEERING FOR LAND DRAINAGE Coefficient for Heavy or Dense SoUs. With respect to more dense soils in localities which have about the same rainfall as those just described, it is observed that the lateral drains must be placed closer together in order to collect the water from the soil and deliver it to the mains, and that the water is absorbed by the soil less quickly. If the lateral drainage has been properly per- formed, the total amount removed will be approximately the same, but its discharge will be extended over a longer time. It is not found to be good practice, how- ever, to use mains of less size on this account, as it is frequently advisable to admit water to the drains by surface-inlets, in which case a pipe of liberal size gives greater efficiency. Some heavy soils found in the south, where the pre- cipitation is greater than in the north, require the aid of surface-inlets or of overflow-ditches. Soils of a "gumbo" and "buck-shot" nature, by which is meant silty clays which are dense and sticky when wet, but exceedingly finely comminuted and tillable when exposed to sun and air, do not permit water to percolate through them readily. Drains placed from 40 to 80 feet apart, the distance depending on the amount of sandy mate- rial which is in the soil, will give good results on level lands. This is costly for lands used for field crops and often will be a sufficient reason, in the landowner's estimation, for not draining at all. A system of com- bined flat-ridging, surface-inlets and tile-drains gives very good service. The ridging consists of plowing the fields in strips, with the furrows running in the direc- tion of the natural slope or the most practicable line of drainage. Lines of 4-inch or 5-inch tile arc then laid about 2j^ feet below the bottom of the dead furrows. The tile should be laid to an accurate grade. Drains laid 100 feel apart whore the dead furrows arc so graded THE RUNOFF FROM UNDERDRAINED AREAS II7 as to not let water stagnate in them will furnish very good drainage at a moderate cost. If the main drains are designed to carry a ^-inch runoff in sections where the annual rainfall is 50 inches, very good drainage will be secured. Surface-inlets need be provided only where there are depressions which are not reached by the surface-drains. CHAPTER IX SIZE OF TILE DRAINS With the information contained in the discussions of flow and runoff in the two preceding chapters, the engineer should be able to determine such sizes of main drains as will be efficient and economical. Good judg- ment, however, must be exercised in selecting a drain- age coefficient and in applying the rule or formula which shall assist the judgment in adjusting sizes to the re- quirements of the land. The engineer should become familiar with the factors which enter into the computa- tions, and be able to use short methods of computing, in which tables play an important part. A few examples are here worked out and explanations given for the purpose of familiarizing him with the methods of work. Application of Formulas. The method commonly used in applying the formulas is to ascume a size of tile which in the judgment of the engineer will be correct, and compute its capacity. A formula so constructed as to give the diameter of the pipe direct is not convenient to use. Remembering that the capacities of pipes laid upon the same grade are to each other approximately' as the squares of their diameters, the proper size can be readily fixed after one or two computations have been made. Advantage should be taken of the tables giving square roots, areas of pipes, etc. Illustrative Examples. Gi\cn a fann of i6o acres, which is to be ch-ained through one outlet. What size of tile should be useil on the lower 1,000 feet of length which has a gnule of .2 foot (2J2 inches) per 100 feet, assuming a drainage coefficient of ^4 inch? 118 SIZE OF TILE DRAINS II 9 Volume to be removed = i6o X .0105 = 1.68 cu. ft. per sec. Assume that a twelve-inch tUe will be required, and use the formula, d = I ft. h = 2 ft. 1 = 1000 ft. 54d = 54 ft. a = .7854 sq. ft. m = 45 Q = a V = °^>ll dh + 5^ («^ Substituting values, 4 2 ^ = 45^1^ = 1-95 Q = '7354 X 1. 95 = 1-53 cu. ft. per sec. Dividing the discharge by .0105, the drainage coefficient taken from Table III, we have, A -■ With ^2 inch coefficient A = 73 Should the additional head furnished by the submains amount to one foot as would probably be the case, V = 2.38 Q = .7854 X 2.38 = 1.86 1.86 A = = 177 •oios It is assumed that the outlet is free. In a large system, local conditions as to head must be taken into account by the engineer and corresponding substitu- tions made in the formula. A 6-inch tile drain, 1,500 feet long, is laid in an open soil on a grade of 3 inches per 100 feet at a general depth of 4 feet, there being 3.5 feet of soil above the top of the drain. With the proper number of branches of 4-inch tile, how many acres of farm land can be efficiently drained through it, the laterals being laid on the same grade as the main, and the drainage coefficient being }4 inch? I20 ENGINEERING FOR LAND DRAINAGE d h 1 a m Dr. coef. Q A .5 ft. 3-75 + 1-75 = 5-So 1527 .1964 36 .0157 (Table m) Substituting in Formula 9 36 jS_X_5:S0 ^ ^ V.'3^i8"= 1.52 \ 1527 .1964 X 1-52 = -296 .296 = 19 •0157 , A fair margin should be allowed in estimating sizes since the engineer may not be correct in his estimate of the effect of soil, topography and weather in their rela- tions to drainage, nor that the material and methods of construction will conform to his specifications. TABLE m Cubic Feet per Second per Acre and per Square Mile that a Drain Must Discharge to Remove Various Depths of Water in 24 Hours Depth in Inches. Cu. Ft. PER Sec. Fraction Decimal Per Acre Per Sq. MUe I 1. 000 .0420 26.88 « ■938 ■0394 25.20 Vs ■875 .0367 23-52 « .812 .0341 21.84 M .750 •03IS 20.16 ii .688 .0289 i8u(8 % .625 .0262 16.80 A .562 .0236 15-12 V2 .500 .0210 13-44 A .438 .0184 11.76 H •375 .0157 10.08 A .312 .0131 8.40 M .250 .0105 6.72 A .188 .0079 5-04 H .125 .0052 3-36 .'. .062 .0026 1.68 SIZE OF TILE DRAINS 121 Table III gives the cubic feet per second, per acre and per square mile, for various drainage coefificients from ^ inch to I inch, expressed in common fractions and in decimals of an inch. Tables for Estimating Sizes of Tile. The foregoing discussions, together with records from various sources regarding the performance of tile in drying land, show that set tables worked out by formulas based upon assumed premises and data can only serve as a general guide in designing the size of mains for underdrainage. The fact that tile drains of the same dimensions and theoretical capacity give varying results under different conditions, as measured by the effect they have upon the land, shows that such conditions should be examined and analyzed by the engineer in the application of formulas and tables. Two tables of sizes of tile and the corresponding number of acres drained by them are here given. Table IV A has been computed on the basis of ^-inch runoff for a length of i,ooo feet outlet section, the conditions being such that the tile flows full, and the outlet is not submerged above the top of the pipe. The latest corrected values of m, Formula 8, as scheduled on page loi, have been u ed. The ^-inch drainage coefificient is generally applicable to localities where the annual rainfall does not exceed 38 inches. For localities having greater rainfall, reduce the number of acres by the following multip'iers: 45 inches .7 55 " -6 60 " .5 Table IV b has been computed by Fonnula 9, using a soilwater head in addition to the slope in computing the velocity. This table may be used in draining the 122 ENGINEERING FOR LAND DRAINAGE TABLE IV A Acres Drained by Tile Mains Computed with Discharge Due Only toSlope and with Tile Flowing Full. Drainage Coefficient Y^ Inch Grade Per 100 Feet. Diameter cr Tile IN Inches EqiTiv Ft. In. b 7 « 31 TO 41 12 66 I') iS 24 30 36 .04 K 9 IS 21 138 197 434 790 1279 •OS ^ ri lb 24 34 45 73 IS6 221 482 884 1427 .oS I 12 20 30 43 51 93 197 278 614 1 122 1810 .10 lA IS 23 33 4« 64 104 219 318 68s I25S 2019 .12 i>i i6 25 36 53 70 114 241 .138 751 1368 2208 .i6 2 19 28 42 6l 8i 133 278 39+ 869 1583 25.58 .20 ^% 21 32 48 69 91 147 311 457 970 1775 2858 .25 3 23 35 53 78 102 I65 347 492 1082 1987 3200 ■30 3H 26 39 SB 84 119 l8o 380 .538 1187 2175 3400 .^3 AY, 30 45 67 97 I2S 208 439 623 1370 2505 4038 •50 6 33 SI 74 lc8 144 233 490 667 1530 2800 4520 .75 9 40 63 92 1J3 175 28s 601 852 1872 3416 5530 TABLE IV B Acres Drained by Tile Mains Computed with Discharge Due to Slope Plus Soilwater Head of 1.5 Feet. Tile Flowing Full. ■ Drainage Coefficient J4 inch Grade per 100 Ft. Diameter of iile i NT Inches Equiv. Ft. 6 7 8 9 10 12 16 iS 34 30 36 .04 y2 20 31 46 66 88 144 252 42s 945 1730 2780 .OS H 21 32 48 69 91 147 3" 442 970 1775 2858 .oU I 22 35 52 73 97 158 333 472 1042 1900 306s .10 lA 23 37 S3 78 104 165 347 492 I113 •985 319s • r2 1/2 24 38 55 80 los 171 360 SI2 1130 ao8o 3320 .16 2 26 40 59 85 "3 183 386 548 laoS 2202 3530 .20 2'A 27 43 62 91 120 195 411 583 12S0 2342 3780 •25 3 29 4S 67 97 128 208 439 623 1370 2503 4038 .30 3H 32 47 71 103 136 221 467 660 1450 2658 4280 .40 4« 34 S" 79 114 i.-io 2.14 S16 730 i6to 2940 4748 .50 6 38 56 86 "3 163 265 556 794 1746 3197 5150 •75 9 44 69 lOI 145 192 312 658 934 2280 3759 6060 SIZE OF TILE DRAINS 1 23 following kind of soils: Permeable and absorbent loams, joint clay loams, marly clays, peat mucks, timber mucks and other types with similar physical properties. The drains are expected to discharge their maximum volume under pressure, a condition which is not detri- mental to lands for periods of short duration. These two tables represent Hmits between which most, if not all, soils in the humid belt will fall, with respect to their drainage requirements. While they express different re- sults where uniformity might be expected, such varia- tions come within the limit of successful drainage' practice. Illustrative Example. A 24-inch tile is laid on a grade of .10 feet per 100 feet and is one mile long. How many acres will it serve as an outlet, provided an adequate system of submains and laterals is connected with it, no allowance being made for additional soil- water or submain head? Use Formula 8 d = 2 ft. h = 5.28 ft. 1 = 5280 54d = 108 ft. a = 3.142 sq. ft. m = 54 = 54-yj 2 X 5-28 , ^ -ggg = 54 V. 00196 = 2.39 Q = 2.39 X 3-14 = 7-50 7-50 A = -^—- = 714 .0105 Drainage areas requiring a 24-inch main will usually have a tributary system of submains and laterals or possibly surface inlets which will increase the head and 124 ENGINEERING FOR LAND DRAINAGE consequent discharge. Suppose that in the above example the lateral system under maximum water conditions should create an additional effective head of 2 feet, making h = 7.28 (Formula 9), Then v.= 2.80 Q = 8.79 A = 836 Size of Laterals. The size of submains and laterals should not be fixed until the lines have been run out and the levels taken. If there are submains, estimate the area which will be drained by each and determine by formula or from a table the size at various controlling points, such as at the junction with the main or where the grades change in a marked manner. The sizes of the balance of the drains are adjusted to fit the con- ditions of the field as shown by the survey and by inspection of the land. Decrease the size of the tile up grade, unless the grade continues to flatten in that direction, in which case the same size may be continued farther up grade to compensate for decrease in slope. No attempt should be made to have the capacity of the mains and submains equal to the combined capacity of the laterals, for the nature of the soil largely controls the distance apart, arid hence the number of laterals. The character of the soil in two tracts may so differ that thorough drainage demands laterals 50 feet apart in one case, and 150 in the other, yet the runoff or discharge may be the same in both, requiring the same capacity of mains and submains. Ordinarily the laterals are re- quired to carry but a small part of their full capacity, and the aeration thus afforded contributes to their value in the soil. Should the system of laterals have a heavy grade as SIZE OF TILE DRAINS I25 compared with that of the mains or submains into which they discharge, the latter will operate under pressure when the rainfall is not very large, causing the water to flow with greater velocity than if the laterals of the system were laid on a flatter grade. This sub- ject has been discussed in connection with formulas for flow. (Chap. VII.) Limitations of Size, Grade and Length of Drain. The modifying factors in the operation of drains, which have been discussed, suggest what has been found true in practice, namely, that there are limits which should be placed upon the size, grade and length of drains and that these limits depend upon the condition of the lands through which the drains run. The minimum size of tile formerly used for laterals was 2 -inch. No smaller than 3-inch is now advised and where grades are light, 4-inch tile are the smallest that should be laid for any purpose. Drains which pass through clay contjjning but little fine sand can be laid on a nearly level grade with no risk of silting up or filling, but in soils containing fine sand, a grade of 2^4. inches or more, per lOO feet, should be secured, if possible, so that the tile will be self-cleaning. The friction in tile of the smaller sizes makes it necessary to limit their length. Beyond the size of i2-inch, however, the formulas for flow may be applied irrespective of the following empirical limita- tions. (See Table V.) Tabulating Tile. After the engineer has determined the number and size of the tile for each drain, he should note them upon the field-book along with other par- ticulars pertaining to the drain. The tile of the entire field, system or district should then be tabulated systematically, in order that a bill of tile according to size can conveniently be made out, and also that they may be distributed in the field without confusion. 126 ENGINEERING FOR LAND DRAINAGE TABLE V Limit of Size of Tile to Grade and Length Size of Tile in Inches Minimum Grade in Feet per 100 Feet Limit of Length in Feet 3 .10 800 4 .06 1,600 5 .06 2,000 6 .06 2,500 7 .06 2,800 8 •OS 3,000 9 •05 3.S00 10 •05 4,000 II .04 4.500 12 .04 5,000 The form given below may be followed in making this list. The last column gives the total length of each separate drain and should be used in checking the work. DISTRIBUTION OF TILE (Example of Form) Drain l2-in. lo-in. 8-in. 7-in. 6-in. 5-in. 4-in. Total Main A No. I 800 1,200 250 4S0 200 1,300 480 1.350 1,100 300 900 600 1,260 4,680 1.350 No. 2 No. 3 300 1,700 1. 500 2,000 No. 4 3SO 450 900 740 500 200 Branch a of No. 4 No. 5 Main B 700 400 No. I of B 600 No. J of B 60a 800 1,200 950 450 950 4,090 6,990 15.430 SIZE OF TILE DRAINS I27 Preliminary Estimate of Tile per Acre. Where a com- plete system of laterals placed at a uniform distance apart is contemplated, it is often desired to estimate roughly the number of feet of tile that will be required per acre. The following tabular statement will assist in making such an estimate. The length of mains re- quired for the system must be added to the total for the entire tract: 20 feet apart, 2,178 feet per acre. 25 1,742 30 {( (( 1,452 33 (( (( 1,320 40 (( (( 1,089 50 (( It 872 66 (( tt 660 80 {( i( S4S 100 ft li 436 ISO u <( 291 200 (( (1 218 Some helpful data and tables are inserted here for use in applying formulas and making computations. CONVENIENT EQUIVALENTS IN MAKING COMPUTATIONS: One acre 43,56° square feet One acre foot 43,56° cubic feet Water one inch deep on one acre 3,630 cubic feet Water one inch deep on one square mile 2,323,200 cubic feet One cubic foot of water weighs 62.4 pounds One cubic foot of water = 7.48 gallons One inch of water on one acre weighs. . .113.43 tons of 2000 pounds Velocity of 1.466 feet per second = i mile per hour Velocity of one foot per second = 682 mile per hour Cubic feet per second X 448-8 = gallons per minute 128 ENGINEERING FOR LAND DRAINAGE TABLE VI Square Roots of Numbers from .i to 20 For Use with Formulas No. Sq, Rt. No. Sq. Rt. No. Sq. Rt. No. Sq. Rt. .1 •316 .8 1^673 •4 2.720 12. 3-464 •IS •387 ■9 1-703 •5 2-739 .1 3-479 .2 •447 3- 1.732 .6 2.757 .2 3-493 •25 .500 .1 1.761 •7 2.775 •3 3-507 ■3 •548 .2 1.789 .8 2^793 •4 3-521 •35 •592 •3 I.817 •9 2.811 •5 3-536 •4 •633 •4 1.844 8. 2.828 .6 3-550 •45 .671 •S 1.871 .1 2.846 .7 3-564 •5 •707 .6 1.897 .2 2.864 .8 3-578 •55 •742 .7 1.924 •3 2.881 •9 3592 .6 •775 .8 1.949 •4 2.898 13. 3.606 •65 .806 •9 1^975 •5 2.915 .2 3633 •7 •837 4- 2. .6 2-933 •4 3^66i •75 .866 .1 2.025 •7 2.950 .6 3^688 .8 •894 .2 2.049 .8 2.966 .8 3-715 •85 .922 •3 2.074 •9 2-983 14. 3-742 •9 •949 •4 2.098 9- 3- .2 3768 •95 •975 •5 2.121 .1 3^017 •i 3-795 I. 1. 000 .6 2.145 .2 3^033 .6 3-821 •05 I^025 •7 2.168 •3 3^050 .8 3-847 .1 1.049 .8 2.191 •4 3^066 15^ 3-873 •15 1.072 •9 2.214 .5 3.082 .2 3-899 .2 1.095 5^ 2.236 .6 3.098 •4 3-924 •25 1. 118 .1 2.258 •7 3^114 .6 3-950 ■3 1.140 .2 2.280 .8 3-130 .8 3-975 35 1. 162 •3 2.302 •9 3-146 16. 4- •4 1. 183 •4 2.324 10. 3-162 .2 4-025 ■45 1.204 •5 2.345 .1 3-178 •4 4.050 •5 I.22S .6 2.366 .2 3-194 .6 4-074 •55 I.24S •7 2.387 •3 3-209 .8 4-099 .6 1.265 .8 2.408 •4 3-22S 17- 4.123 •65 1.285 •9 2.429 •5 3-240 .3 4.147 •7 1.304 6. 2.449 .6 3^256 •4 4.171 ■75 i^323 .1 2.470 •7 3^271 .6 4^195 .8 1.342 .2 2.490 .8 3-286 .8 4.219 ■85 1.360 •3 2.510 •9 3-302 18. 4^243 ■9 i^378 •4 2.530 II. 3^317 .a 4.266 •95 1.396 •5 2.550 .1 3-332 •4 4.290 2. 1.414 .6 2.569 .a 3-347 .6 4313 .1 1.449 •7 2.588 •3 3-362 .8 4-336 .2 1.483 .8 a. 608 .4 3-376 19. 4-359 >3 1.517 •9 2.627 •5 3-391 .2 4-382 •4 '•549 7- 2.646 .6 3-406 •4 4-40S •I 1. 58 1 .1 2.665 •7 3-421 .6 4-427 .6 1.612 .2 2.683 .8 3-435 .8 4-450 •7 1.643 •3 2.702 •9 3-450 20. 4.47a SIZE OF TILE DRAINS 129 TABLE VII Areas of Tile in Square Feet; also 54d For Use with Formulas Diam. in Ins. Diam. in Ft. Area in Sq. Ft. S4d 2 .1667 .0218 9.00 3 .2500 .0491 13.50 4 •3333 .0873 18.00 5 .4167 •1363 22.50 6 .5000 .1964 27.00 7 •5833 .2673 31-50 8 .6667 .3491 36.00 9 .7500 .4418 40.50 10 •8333 -5454 45-00 II .9167 .6600 49-50 12 I foot ■7854 54-00 13 1.083 .9218 58-50 14 1. 167 1.069 63.00 15 1.250 1.227 67-50 16 1-333 1.396 72.00 17 1.417 1.576 76.50 18 1.500 1.767 81.00 19 1.583 1.969 85.50 20 1.667 2.182 90.00 21 1.750 2.405 94-50 22 1-833 2.640 99.00 23 1.917 2.885 103.50 24 2 feet 3.142 108.00 25 2.083 3409 112.50 26 2.166 3.687 117.00 27 2.250 3-976 121.50 28 2.333 4.276 126.00 29 2.416 4-587 130.50 30 2.500 4.909 135-00 31 2.584 5.241 139-50 32 2.666 5-585 144.00 33 2.750 5-940 148.50 34 2.834 6-305 153.00 35 2.916 6.681 157-50 36 3 feet 7.069 162.00 I30 ENGINEERING FOR LAND DRAINAGE TABLE Vin Head in Inches Reduced to Feet For Use with Formulas Head in Ins. per 100 Ft. Head in Ft. Head in Ft. Head in Ins. per 100 Ft. Head in Ft. Head in Ft. per 100 Ft. per Mile per 100 Ft. per Mile A .0052 .274 3 Vs .0104 •549 Yb .2604 13-749 H .0208 1.098 M .2708 14.298 Vs •0313 1.652 Vs .2813 14-852 Yi .0417 2.201 Y2 .2917 15-401 H .0521 2.750 Vs •3021 15-950 M .0625 3-300 M •3125 16.500 Vs .0729 3.849 Ys -3229 17.049 I .0833 4-398 4 -3333 17-598 Vs .0938 4-952 Y% -3438 18.153 y4, .1042 5-Soi Ya .3542 18.702 H .1146 6.050 y% .3646 19-251 Yi .1250 6.600 Yi -3750 19.800 % •1354 7.149 Ys -3854 20.349 % .1458 7.698 Yi -3958 20.898 Vi •1563 8.252 Ys .4063 21-453 2 .1667 8.801 5 •4167 22.002 Ys .1771 9-350 Ys .4271 22.551 M •1875 9.900 Ya. •4375 23.100 % .1979 10.449 y% -4479 23.649 Y2 .2083 10.998 Y2 •4583 24.198 Ys .2188 "•552 Ys .4688 24-753 H .2292 12.101 H .4792 25.302 Ys .2396 12.650 Ya .4896 25.851 3 .2500 13.200 6 .5000 36.400 SIZE OF TILE DRAINS I3I TABLE IX.— Table of Feet in Decimals of a Mile 0.000 o.oor 0.002 0.003 0.004 0.005 0.006 0.007 o.ooS 0.009 Miles Ft. Ft. Ft. Ft. Ft. Ft. Ft. Ft. Ft. Ft. 0.00 5 11 16 21 26 32 37 42 48 O.OI 53 S8 63 69 74 79 84 90 95 100 0.02 106 III 116 121 127 132 137 143 148 153 0.03 158 164 169 174 180 185 190 195 201 206 0.04 211 216 222 227 232 238 243 248 253 259 0.0s 264 269 275 280 28s 290 296 301 306 312 0.06 317 322 327 333 338 343 348 354 359 364 0.07 370 375 380 38s 391 396 401 407 412 417 0.08 422 428 433 438 444 449 454 459 465 470 0.09 47S 480 486 491 496 502 507 512 S17 523 O.IO 528 533 539 544 549 554 560 565 570 576 O.II S8l 586 591 597 602 607 612 618 623 628 0.12 634 639 644 649 655 660 663 671 676 681 0.13 686 692 697 702 708 713 718 723 729 734 O.I4 739 744 750 755 760 766 771 776 781 787 0.15 792 797 803 808 813 818 824 829 834 840 0.16 845 850 8S5 861 866 871 876 882 887 8,2 0.17 898 903 908 913 919 924 929 935 940 945 0.18 950 956 961 966 972 977 982 987 993 998 0.19 1003 1008 1014 1019 1024 1030 1033 1040 1045 1051 0.20 1056 1061 1067 1072 1077 1082 1088 1093 1098 1104 0.21 1109 U14 IZ19 II2S 1130 I135 1 140 I146 I151 1 156 0.22 1162 1167 1172 II77 1183 1 188 "93 1199 1204 1209 0.23 1214 1220 1225 1230 1236 1241 1246 1251 1257 1262 0.24 1267 1272 1278 1283 1288 1294 1299 1304 1309 1315 0.2s 1320 132s 1331 1336 1341 1346 1352 1357 1362 1368 0.26 1373 1378 1383 1389 1394 1399 1404 1410 1415 1420 0.27 1426 1431 1436 I44I 1447 1452 1457 1463 1468 1473 0.2S 1478 1484 1489 1494 1500 1505 1510 IS15 1521 1526 0.29 1531 1536 1542 1S47 15S2 1558 1563 1568 1573 1579 0.30 1584 1589 1595 1600 1605 1610 1616 162 1 1626 1632 0.31 1637 1642 1647 1653 1658 1663 1668 1674 1679 1684 0.32 1690 169s 1700 1705 1711 1716 1721 1727 1732 1737 0.33 1742 1748 1753 1758 1764 1769 1774 1779 1785 1790 0.34 I79S 1800 1806 i8ii 1816 1822 1827 1832 1837 1843 0.3s 1848 1853 1859 1864 1869 1874 1880 18 5 1890 1896 0.36 1901 1906 191 1 1917 1922 1927 1932 1938 1943 1948 0.37 1954 1959 1964 1969 1975 1980 1985 1991 1996 2001 0.38 2006 2012 2017 2022 2028 2033 2038 2043 2049 2054 0.39 2059 2064 2070 2075 2080 2086 2091 2096 2101 2107 0.40 2112 2117 2123 2128 2133 2138 2144 2149 2154 2160 0.41 2i6s 2170 2175 2181 2186 2191 2196 2202 2207 2212 0.42 2218 2223 2228 2233 2239 2244 2249 225S 2260 2265 0.43 2270 2276 2281 2286 2292 2297 2302 2307 2313 2318 0.44 2323 2328 2334 2339 2344 2350 23SS 2360 2365 2371 0.45 2376 2381 2387 2392 2397 2402 ;408 2413 2418 2424 0.46 2429 2434 2439 2445 2450 2455 2460 2466 2471 2476 0.47 2482 2487 2492 2497 2503 2508 2513 2519 2524 2529 0.48 2534 2540 2545 2550 2556 2561 2566 2571 2577 2582 0.49 2587 2592 2598 2603 2608 2614 2619 2624 2629 2635 ' Prepared by James G. VVishart. 132 ENGINEERING FOR LAND DRAINAGE TABLE IX. — Continued 0.000 O.OOI 0.002 0.003 0.004 0.00s 0.006 0.007 0.008 0.009 Miles Ft. Ft. Ft. Ft. Ft. Ft. Ft. Ft. Ft. Ft. 0.50 2640 2645 2651 2656 2661 2666 2672 2677 2682 2688 0.51 2693 2698 2703 2709 2714 2719 2724 2730 2735 2740 0.S2 2746 2751 2756 2761 2767 2772 2777 2783 2788 2793 O.S3 2798 2804 2809 2814 2820 282s 2830 283s 2841 2846 0.54 2851 2856 2862 2867 2872 2878 2883 2888 2893 2899 o.SS 2904 2909 2915 2920 2925 2930 2936 2941 2946 2952 0.56 2957 2962 2967 2973 2978 2983 2988 2994 2999 3004 0.S7 3010 301S 3020 3025 3031 3036 3041 3047 3052 3057 0.58 3062 3068 3073 3078 3084 3089 3094 3099 310S 3110 0.59 3115 3120 3126 3131 3136 3142 3147 3152 3157 3164 0.60 3168 3173 3179 3184 3189 3194 3200 320s 3210 3216 0.61 3221 3226 3231 3237 3242 3247 3252 3258 3263 3268 0.62 3274 3279 3284 3289 329s 3300 330s 33" 3316 3321 0.63 3326 3332 3337 3342 3348 33S3 3358 3363 3369 3374 0.64 3379 3384 3390 3395 3400 3406 34" 3416 3421 3427 0.6s 3432 3437 3443 3448 3453 3458 3464 3469 3474 3480 0.66 3485 3490 3495 3501 3506 35" 3Sl6 3522 3527 3532 0.67 3538 3543 3548 3553 3S59 3564 3569 3575 3580 358s 0.68 3590 3596 3601 3606 3612 3617 3622 3627 3633 3638 0.69 3643 3648 3654 3659 3664 3670 3675 3680 368s 3691 0.70 3696 3701 3707 3712 3717 3722 3728 3733 3738 3744 0.71 3749 3754 3759 3765 3770 3775 3780 3786 3791 3796 0.72 3802 3807 3S12 3817 3823 3828 3833 3839 3844 3849 0.73 3854 386a 386s 3870 3876 3881 3886 3891 3897 3902 0.74 3907 3912 3918 3923 3928 3934 3939 3944 3949 3955 0.75 3960 396s 3971 3976 3981 3986 3992 3997 4002 4008 0.76 4013 4018 4023 4029 4034 4039 4044 4050 4055 4060 0.77 4066 4071 4076 4081 4087 4092 4097 4103 4108 4113 0.78 41 18 4124 4129 4134 4140 414s 4150 4155 4161 4166 0.79 4171 4176 4182 4187 4192 4198 4203 4208 4213 4219 0.80 4224 4229 4235 4240 424s 4250 4256 4261 4266 4272 0.81 4277 4282 4287 4293 4298 4303 4308 4314 4319 4324 0.82 4330 4335 4340 4345 4351 4356 4361 4367 4372 4377 0.83 4382 4388 4393 4398 4404 4409 4414 4419 4425 4430 0.84 4435 4440 4446 4451 4456 4462 4467 4472 4477 4483 0.85 4488 4493 4499 4504 4509 4514 4520 4525 4530 4536 0.86 4541 4546 455 1 4557 4562 4567 4572 4578 4583 4588 0.87 4594 4599 4604 4609 4615 4620 4625 4631 4636 4641 0.88 4646 4652 4657 4662 466S 4673 4678 4683 4689 4694 o.8g 4699 4704 4710 471S 4720 4726 4731 4736 4741 4747 0.90 4752 4757 4763 4768 4773 4778 4784 4789 4794 4800 0.91 4805 4810 4815 4821 4826 4831 4836 4842 4947 4852 0.92 4858 4863 4868 4873 4879 4884 4889 489s 4900 490s 0.93 4910 4916 4021 4926 4932 4937 4042 4947 4953 4958 0.94 4963 4968 4974 4979 4984 4990 4995 5000 SOOS 5011 0.9s 5016 5021 SO27 S032 5037 S042 SO48 S053 5058 S064 0.96 5069 5074 5079 5085 5090 5095 Sioo S106 SI" 5116 0.97 5122 5127 5t32 S137 5 143 SI48 5153 S159 5164 S169 0.98 SI74 5180 518s 5190 S196 5301 5206 5211 S2I7 5222 0.09 5227 5232 5238 5243 5248 5254 5259 5264 5269 S27S CHAPTER X SELECTION OF DRAIN TILE Two general classes of clay tiles are known as com- mon clay tile and vitrified tile. Common clay tile are made from common brick clay which is sufficiently plastic to allow moulding easily and when well burned the quality is similar to a firm building brick. They are very generally used for land drainage, and tiles of this quality which have been in use for a hundred years or more attest their durability and efficiency for the purpose. They should give a clear ring when struck with a piece of iron or steel, should be round and rea- sonably symmetrical and straight. They are made in one-foot lengths up to lo-inch, above which size they are frequently made 1 8 to 24 inches long, and the very large ones 36 inches long. The degree of hardness varies greatly in ordinary tile, as does their ability to endure freezing and thawing when lying on the ground during the winter season in northern climates, or when exposed to the weather while in service, as are outlet tiles. Under such conditions many of them scale and crumble, but those which are placed in the ground while sound are durable and in every way satisfactory, provided they have been well burned. It is not essential that the ends be true, since a little space between the tile is needed for the entrance of water. If the ends are slightly beveled, as they usually are, the separate pieces can be laid in a straight line and upon a true grade with a little space at the bottom of the joint, but with the top tightly closed. 133 134 ENGINEERING FOR LAND DRAINAGE Vitrified tile are made of ground shale or of a high grade clay, frequently mixed with common clay. This material will endure greater heat than the com- mon clay and possesses elements that will fuse and form a hard mass which has greater strength and is less absorptive than tile made of common clay. The quality of such tile, however, varies greatly as the tests for resistance to crushing indicate that over-burning the ware may make it brittle and impair its strength. Care should be used in selecting tile for deep ditches. The tough and strong tile are those of medium burn and hardness, and are usually straight. Second-class sewer pipe, with sockets, are frequently offered by manufacturers at prices which will warrant their use for drains. If the bad pieces are rejected they make excellent drains where large mains are needed, and the sockets often facilitate their use in making drains through soft material. If necessary, the joints for short distances can be cemented where especially unstable soil is encountered. The sizes of tile are designated as 8-inch, 12-inch, 18-inch, etc., the numbers referring always to the in- side diameter, regardless of the thickness of the walls. Junction-tile are made to facilitate connection of branch- es. These appear in two forms, known as Y's and T's. The former should always be used at the junction of two lines, having the stem joined to the main line at an angle between 45° and 60°. (Fig. 27.) T's are used only for connecting catch-basins and surface-inlets with drains. These junction-tile are valuable accessories, and should be purchased if possible, as tlie practice of making junctions of various kinds in tlie fields by chipping holes in straight tile is not to be recommended. Junctions are lisLctl by manufacturers by naming the size of the main and its brunch arm, as 6 x 4, which means a junc- SELECTION OF DRAIN TILE 1 35 tion for connecting a 4-inch branch with a 6-in. main, or it is sometimes referred to as a 4-inch on a 6-inch, which is the clearer method of expression. Curved tile, designated as one-eighth and one-quarter bends, are occasionally needed in the construction of large drains, but usually the curves in drains may be made so long that straight pipe can be used if the ends are slightly beveled by chipping. (Fig. 27.) Large Tile. When tile 12-ins. to 36-ins. diam. are used for mains, they usually encounter conditions which are quite different from those met in field drainage. They are laid deeper and not infrequently pass through quicksand and other unstable earth which subjects them to great weight when the trench is filled with loose and liquid-like earth and when the earth at the sides of the trench is in a similar condition. Saturated earth weighs about 100 pounds per cubic foot, so that a pipe covered with earth to a depth of 8 feet would be required, when the soil is saturated, to support a pressure of 800 pounds per square foot, besides that upon the sides in case the earth were soft and unstable. The pressure, however, diminishes as the earth begins to dry, since it partly supports its own weight by the cohesion of its particles. The large volume of water which flows through the larger pipes produces eddies at joints which are too large, or where there are imperfections in the align- ment, and these sometimes cause the tiles to drop out of position. The latter should be sufficiently perfect to permit their being laid with as close joints as may be found necessary. The strength of large-sized tiles should be as great as that required for standard sewer pipe. 136 ENGINEERING FOR LAND DRAINAGE TABLE X Specifications for Standard Sewer Pipe Adopted by Manu- facturers East of the Illinois-Indiana State Line Inside Diaiaeter in Ins. Thickness of Walls in Ins. 3 and 4 H 5 and 6 Vi 8 Va. 9 M ID Vi 12 I 15 ^y% i8 iM 20 i^ 22 1^ 24 iM In sizes above. i2-in. what are known as double-strength pipes are to be had, in which the walls are somewhat thicker in proportion to the diameter than in Standard pipe. Tests of clay pipe of all classes show a wide range of resistance to crushing. The following tests of standard sewer-pipe bedded in sand, with weight applied to the entire length, shows the weight per foot of length at which they broke.* 8-inch 1)363 to 2,256 pounds 12 „ 1,227 " 2>7S6 " 15 464 " 2,093 " * From Folwcll's "Sewerage." SELECTION OF DRAIN TILE 137 RECORD NO. 5 * Breaking Strength of Common Clay Tile Tested by weights placed upon a platform resting on top of the tile; sides of tile unsupported Length, Ins. Diameter Ins. Thickness of Walls, Ins. Breaking, Pounds per Lin. Ft. Remarks 24 12 1,287 Medium burned 24 12 1,168 (( it 24 12 938 (( (f 24 IS 1,032 If u 24 15 1,193 it it 12 6 Vi 990 «( tt 12 6 % 1,060 i( tt 12 6 y% 81S Medium soft * Tests by Albert Beymer, Rocky Ford, Colorado. Relation of Absorptive Property and Strength. A general relation exists between the percent of water which a tile will absorb and its resistance to breaking when subjected to a uniform weight. Toughness, that is resistance to breakage from sudden blows or shocks incident to rough handling, is highly desirable. Some ware having low absorption is tender or brittle, while a comparatively soft and highly absorptive tile may be tough. The following table has been compiled from laboratory experiments to determine the comparative absorptive properties of tiles and their resistance to crushing. The samples tested were taken from different factories and represent merchantable drain-tile. The pieces were first thoroughly dried by being placed in a steam boiler room, and afterwards immersed in water for 72 hours. The amount of water absorbed 138 ENGINEERING FOR LAND DRAINAGE is given in percent of the weight of the dry tiles. The same tiles were tested for crushing strength in a labora- tory testing machine. The pieces of tile were embedded in sand in a box which was furnished with a movable top, prepared for the purpose, and the weight was ap- plied lengthv/ise along the top. The weight under which each piece broke is given in pounds per lineal inch of tile. RECORD NO. 6 * Amount of Absorption and Crushing Strength of Clay Tile Samples 3 inches diameter, 12 inches long, with walls % inch thick Number of Sample Average Break- ing Strength Pounds per Lin. In. Average Percent Absorption ■ I 276 6 Round 2 170 18 3 162 14 " soft 4 173 23-S " If 5 161 19 If ft 6 195 3.64 " glazed 7 IS4 S 4-in. hexagonal vitrified 8 279 1.2 3-m. K II 9 186 21. Sole tile(flat bottom) soft 10 121 22.9 II II II <■ II * Tests made by J. R. Haswell in laboratory of Cornell Uni- versity, Ithaca, N. Y., 1909. Since the samples were supported rigidly at the sides, the breaking test is much higher than it would be under tests as they are usually made, and the record is given here for comparison only. The tests show the great variation in the amount of water which tiles will absorb. The hard-burned ware absorb 2% to 6% of its dry weight of water, and the soft-burned, 14% to 23%. SELECTION OF DRAIN TILE 1 39 The former broke under a load of 195 to 276 pounds per lineal inch, the latter under a load of 121 to 173 pounds. These results indicate that as a class hard-burned tiles are about 60% stronger than soft ones having the same thickness of walls. When subjected to reasonably uni- form pressure tiles break lengthwise into four nearly equal pieces. Porosity of Drain-Tile. Notwithstanding the large absorptive properties possessed by the softer grades of clay tile, water will not pass through their walls under the pressure to which they are subjected in the soil in sufficient quantity to be of any service in drainage. The term "porous tile" arises from the avidity with vliich dry tile will absorb water until it becomes saturated, but the water does not pass through in any appreciable quantity, being retained in the pores until removed by capillary action and by evaporation. This fact was demonstrated as early as 1846 by Josiah Parkes, consulting engineer for the Royal Agri- cultural Society of England. He also attempted to secure greater permeability of the walls by having small holes pierced in them before drying. The clay quickly filled the holes after the tiles were placed in the ground, and Mr. Parkes concluded that the water which flowed from drain-tile entered them at the joints. This has been the subject of experiments at different times, and the conclusion has been reached, in every case, that the porous property in tile has no value for draining. An experiment was made by Drainage Investiga- tions, U. S. Department of Agriculture, under the direction of the author, in 1910, which illustrates this property fairly well. Two 6-inch and two 3-inch drain-tile made out of common brick clay, burned a salmon color, and as soft 'as . are usually considered safe to use, were sealed at one end with cement mortar. 140 ENGINEERING FOR LAND DRAINAGE They were then immersed in water until they became saturated and afterward placed in a tank of water in which the surface was kept within a quarter of an inch of the top of the tiles. The tiles were covered so as to prevent any loss of water which percolated through the walls. The depth of water which accumulated in each of the tiles was measured at the end of four, twenty-four, forty-eight, and seventy-two hours, and the volume in cubic feet and gallons computed. The experiment was then reversed, the tiles being filled with water, and the amount which percolated through the walls collected in a saucer and measured. During this part of the ex- periment, the tiles were placed in a damp closet so that no water would be lost by evaporation. The results were as follows: Taking the average of the measure- ments, the four tiles showed a percolation of about .0049 cubic foot per square foot of surface in 24 hours. If an acre of ground were drained with lines of 6-in. tile of this quality, placed 50 feet apart, the total volume of water which would pass through the walls in 24 hours would be 6.92 cubic feet or 51.7 gallons. This is on the assumption that free water instead of saturated soil would surround the tile. If water entered only through the pores it would require 139 days to remove y^ inch in depth of water from the acre, tiled in that manner, and 250 days if 3-in. tile of the kind experimented with were used. But drains so laid are capable of removing that volume of water from the soil in 24 hours. These facts have been recognized for half a century by drainage engineers and by writers upon practical drainage, yet the porosity of tile as an important con- tributing factor in their use in draining land continues to be erroneously taught in agricultural literature, and occasionally by engineers who have only a theoretical knowledge of the subject. SELECTION OF DRAIN TILE I4I Concrete Tile. The use of concrete for drain- til j has grown so rapidly during the last few years that it now occupies an important place in drainage works. Many expensive mistakes have been made in develop- ing the manufacture of concrete, or cement, tile, and the occasional failures of imperfect pipe subject them to sharp criticism. The need of standard specifications upon quality of material and method of manufacture is appreciated by the drainage fraternity generally, and it is hoped that some standard which can be relied upon will soon be adopted. It is clear that first-class Portland ce- ment and good sand should be used, and that they should be properly mixed. In order to obtain a dense, non- porous tile, the mixture should be wet, as opposed to what is known as " dry mixture." The proportion of I part good Portland cement to 3 parts of good sand, well mixed, produces a good tile. The practice is to make the walls somewhat thicker than those of clay tile, since the tests for strength generally show that cement tile are weaker than clay tile with equal thickness of walls. This, however, is a point not well established, as the results of tests vary greatly. The test for density is the ring which the pipe give when they are struck with a piece of steel. In selecting concrete tile, the engineer should know the quality of the material used and the manner of making them. The value and stability of such tile depend so largely upon these two things, that both consumer and manufacturer feel the need of well-tested and standard methods which when used will insure tile of uniform and reliable quality. Abundant examples of tile now in service prove quite conclusively that well-made cement tile meet every requirement in drainage. Any failure of them indicates imperfections in their manu- facture which need not have occurred. 142 ENGINEERING FOR LAND DRAINAGE The tendency of present drainage practice is toward the use of systems which require large tile outlets, some- times placed at considerable depths. The requirements of drains under such conditions as far as strength is concerned are not definitely known, though experiments are being conducted at various points for the purpose of securing such information. In the meantime, the author advises that pipe twelve inches or more in dia- meter when placed at greater depths than four feet, be required to stand a test for crushing equal to that of ordinary standard sewer pipe, with the hope that stan- dard specifications for the strength of both clay and cement drain-tile will soon be satisfactorily determined. Small tile for field use at ordinary depths are sufficiently strong if they sustain a weight of 800 pounds per lineal foot when the weight is placed along the medial line on top of the sample and the sides are unsupported. CHAPTER XI CONSTRUCTION OF TILE-DRAINS The engineer should be entrusted with the super- vision, inspection, and acceptance of the work he lays out, and for that reason should be thoroughly versed in the details of grading ditches and tile-laying. If neces- sary he should instruct workmen regarding the essential points of the construction of underdrains. An appren- ticeship of greater or less duration is required to develop a skilful drainer. The work is deservedly passing into the hands of those who by practice have acquired a proficiency which is readily acknowledged by those who appreciate superior work in draining. The engineer, however, may not be so fortunate as to secure such ser- vice, but be compelled to train new men to perform the work. The introduction of successful trenching ma- chines has added an encouraging impetus to under- drainage, but whether the work is done by hand-labor or with the aid of power machines, the requirements of a well-laid tile-drain remain the same. For these reasons it is thought best to here describe the work in detail as the engineer may not have had the oppor- tunity to inform himself fully upon the best practical methods of construction. Grading. One of the most practical of the several methods of setting a guide for the workman in grading the bottom of the trench is the line and gage method. This consists in setting a line at a convenient distance above the surface so that it shall be parallel to the bot- tom of the required ditch. The position of the line is 143 144 ENGINEERING FOR LAND DRAINAGE shown in Fig. 24, If the ditch is 3 feet deep, the line e may be set 5 feet above the bottom. To do this, sub- tract the depth indicated for the ditch at the stakes c and d from 5 feet. The result will be the height above the grade-stakes that the line should be placed. It should be drawn tight and fastened as shown in the figure. If the distance between stakes is 100 feet, a support stake should be placed midway to prevent the line from sagging. The method of using the line is shown in Fig. 25. A gage-rod, ab, five feet long, or any other length according to the height at which it may be Fig. 24. — Guide-line for Grading. found convenient to set the line, is held vertically, with the under edge of the arm b touching the line e. The bottom of the ditch, f, is dressed down so that when tested by the gage the arm touches the line. In this manner the bottom can be graded so as to be exactly parallel with the line e and at the required depth. Each foot of ditch should be tested by tlie gage as the excava- tion proceeds. Where excavation is performed by a machine which completes the ditch at one passage, guides are set in advance of the machine as shown in Fig. 26, where a represents the bar, or sighting point on the machine, which is at a fixed distance above the bottom of the finished ditch. Tlic guide-arms, which may be adjust- CONSTRUCTION OF TILE-DRAINS 145 able on the standards b, c and d, are set the same dis- tance above the proposed grade-line, their position be- ing determined in the same manner as that described for setting the line e in the figure. As the machine moves forward toward the guides, the sighting-point, a, is made to coincide with the line of sight passing over two or more of the guide-bars, and the bottom of the ditch is finished parallel to the sight line ae, and according to the requirements of the survey. Excavating Trenches. The work should be started at the outlet and proceed up grade. The ditch should be started straight on the surface and the curves should be regular and neatly cut. To accom- plish this the workman needs a ^-inch rope which can be drawn tight along one side of the ditch or can be laid to form neat curves. The top width should be proportioned to the depth to which it is to be made, 10 inches being the min- imum. A ditching spade with blade 18 or 20 inches long, slightly curved forward and straight across the cutting edge, or the same form of blade with longitu- dinal bars and a cutting edge instead of a solid piece, is used for all digging which does not require a pick and steel bar. The workman opens the ditch with the spade, using the cord, which has already been placed in position, as a guide. After taking out the first spading, the loose earth, of which a skilful workman will leave but little, should be removed with the long-handled Fig. 25. — Method of Using Grade-line. 146 ENGINEERING FOR LAND DRAINAGE round-pointed steel shovel which is a part of the ditcher's outfit. If the ditch is about 3 feet deep, it can be ex- cavated at two spadings, if 4 feet, three spadings will be required. The bottom is finished as the last spading is removed, care being taken not to let the spade pene- trate deeper than the grade-line. The guide-line hav- ing been set, the cleaning-scoop is brought into use to Fig. 26. — Guides for Trenching-machine. clean the loose earth from the bottom and bring it to an accurate grade. The workman stands upon the last bench and grades such a part as he can reach with the cleaning scoop, then opens more of the trench with the spade. The accuracy of the bottom is tested at any desired point by means of the gage, whose use is shown in Fig. 25. If the trench is large or the bottom hard and difficult to work with the scoop, the workman must make the trench wide enough to enable him to stand on the bottom and grade the bottom with the shovel. In any case, the bottom should be smooth and accu- rately graded. The importance of starting the top of the ditch straight will be appreciated when the bottom is reached, for it will there be found that the crooks at the top appear in more pronounced form. While the construction of large and deep ditches involves diffi- CONSTRUCTION OF TILE-DRAINS I47 culties peculiar to themselves, the principles relating to the preparation of the bottom will apply to all cases. Laying the Tile. If the bottom has been well pre- pared, tile-laying, which should begin at the outlet, will be easily done. Sizes which can be conveniently handhd may be laid with a tile-hook by the workman as he stands upon the surface. Some workmen prefer to place the tile in position with their hands while stand- ing in the ditch. If the grading has been well done, the tile will fit the bottom perfectly and can be laid as accurately with the hook and with much more ease. The tile should be turned about until the ends fit closely -ear in which to excavate through soil known to contain quicksand, and, second, to lay the drain as far into the treacherous soil as can be done safely, and stop the work for a time until the quantity of water is lessened by gradual percolation, then proceed. It may take a month or two to pass through a bad place, but it will be safer and cheaper to proceed in this manner than to force the work through more rapidly. As an aid to solidifying the mass of unstable earth so that it CONSTRUCTION OF TILE-DRAINS 1 55 can be handled, temporary drains may be laid as far as possible, and above grade, in order to draw off surplus water. In case quicksand is unexpectedly encountered and it is necessary to continue the work without interruptions, tight sheathing with strong braces must be resorted to. The sheathing planks of 2-inch material must be driven endwise asdeep as the grade of the ditch, the excava- tion proceeding as the planks are driven down. The strength and frequency of the braces required will de- pend upon the condition of the earth. This method is slow and expensive, but is often required in constructing deep drains. To prevent sand from entering the pipe at the joints, tarred paper, burlap, coarse hay or grass, or small bun- dles of fine twigs laid closely about the joints and covered with firm clay are always helpful. The best material for this purpose, however, is coarse gravel and should be used whenever it can be obtained. Sewer pipe with sockets are more easily laid in such earth than common tile. It is frequently necessary to place a board in the bottom of the trench upon which to support the pipe. When there is risk of slumping or caving banks, the sheathing planks should be resorted to. In working under these difficulties every pipe should be tested for grade and alignment before it is passed. Some method for doing this should be devised by the engineer to suit the exigencies of the case. During the construction of a drainage system, the work is often hindered in the spring of the year by heavy rains which fill the trenches that have been dug and submerge the lines of tile already laid. In the case of mains with light fall there is considerable risk from earth and silt which may be washed into the drain and par- 156 ENGINEERING FOR LAND DRAINAGE tially obstruct it. It is better to drive screen-stakes at tiie opening of the drain to prevent the entrance of coarse material and allow the flood to fill the tile, than to close the end and cause the entire volume to flow over the top of the drain. Cleaning Tile-Drains. Notwithstanding that all pos- sible care may have been taken to prevent mud and sand from entering tile during the construction of the drain, it frequently occurs that they will be found more or less obstructed from this cause. If the tile are in the required position, and are all right with the excep- tion of the obstruction, do not disturb them but remove the material by one of the following suggested methods. Remove the earth from over the drain at intervals of twenty-five feet, exposing a length of about three feet at each place. Take out the tile and remove all silt that can be conveniently reached. If the tile are less than half full of mud and there is water enough in the pipe to make the material soft, place a bundle of stiff straw in a strong canvas sack of such size that it will partly fill the bore of the drain. Attach a rope securely to the sack and pass it through the drain from one opening to the other. This can be done by means of a set of jointed sewer rods which will be found useful in the various kinds of drain cleaning. The rods are made of wood one inch in diameter and 3^ feet long, provided with a loop at one end and a hook at the other, so shaped that they can be joined when placed at a right-angle to each other, but when opened out straight will remain fast together. The end of the rope may be pushed through the drain by the rods, length after length being attached until the rope is forced to the next opening in the drain. By means of the rope pull the swab through the drain, and as the material is forced to the opposite end let it be dipped or shoveled out. It is well to have a rope CONSTRUCTION OF TILE-DRAINS 157 attached to each end of the swab so that it can be drawn back and the operation reversed. Instead of the canvas-bag swab, a metallic brush, which is constructed as follows, may be used. A wooden cylinder 4 feet long and of a diameter propor- tionate to the tile to be cleaned, serves as a center, or core, for the brush. A sheath of heavy leather, of a size to cover the core, is pierced with sharp-pointed steel wire nail's with flat heads at about 3 inches apart. These are driven through the leather, which is then fastened securely to the core with the points of the nails outward. The nails are two, and for large tile, three inches long, and being adjustable by reason of the flexibility of the leather through which they are inserted, they accommodate themselves to the opening in the tile and at the same time loosen and push out the mud as the brush is drawn back and forth. If the material in the tile is too solid to permit the use of the swab or brush, a small hinged spud or hoe may be made and operated by using the jointed rods as a handle. The hoe should be about 3 inches square and have a hinge joint which will permit it to close when the tool is thrust into the mud and open as it is pulled back. This loosens the mud and also enables the workman to pull it to the opening. Care should be taken in replacing the tile to preserve the original alignment. A little mud or sand will always remain in the drain after it has been scoured in this way, but it will be readily washed out when the drain is flushed, provided the latter is otherwise in perfect condition. It will be wise to construct occasional sand-traps on portions of the line where it is suspected that sand will interfere with the operation of the drain. Specifications and Contracts. It is usually desirable to have large drainage systems constructed by contract. 158 ENGINEERING FOR LAND DRAINAGE There are four divisions of the work: Furnishing the tile on the cars at the nearest railway station ; hauling them from the station and distributing them upon the ground ready for use; digging the ditches and laying the tile; and back-filling the trenches. Tile are purchased at a rate per 1,000 feet. They are hauled from the station or factory and distributed on the ground at a price per ton of 2,000 pounds, the weight of the individual pieces of different sizes being used as a basis- for determining the weight of the loads. Digging ditches and placing the tile in position are commonly contracted by the rod or 100 feet as a unit; ditches are filled at a price per 100 feet. The following suggested specifications will serve as a guide to the engineer and may be modified as required to meet special cases. Engineer's Stakes. — The lines for the ditches are indi- cated on the field by stakes which have been set by the engineer, and the depths and grades given by him con- stitute a part of the specifications. Digging the Ditches. — ^The digging of each ditch must begin at its outlet, or at its junction with another tile- drain, and proceed toward its upper end. The ditch must be dug along one side of the line of survey-stakes, and about ten inches distant from it, in a straight and neat manner, and the top soil thrown on one side of the ditch and the clay on the other. WTien a change in the direction of ditch is made, it must be done by means of a neat curve, but in all cases the ditch must be kept near enough to the stakes so that they can be used in grading the bottom. In taking out the last draft, the blade of the sjiade must not go deeper than the proposed grade-line or bed upon which the tiles are to rest. Grading the Bottom. — The ditch must be dug tc tne CONSTRUCTION OF TILE-DRAINS j^g depth indicated by the figures given with the survey, which depth is to be measured from the grade-stakes which are set for that purpose, and graded evenly on the bottom by means of the line and gage method, target, or any other equally accurate device for obtain- ing an even and true bottom upon which to lay the tile. The bottom must be dressed with the tile-hoe, or, in case of large tiles, with the shovel, in such a way that a groove will be made to receive the tile, so that when laid in it they will remain securely in place. Laying the Tile. — The laying of the tile must begin at the lower end and proceed up-stream. The tile must be laid as closely as practicable, and in lines free from irregular crooks, the pieces being turned about until the upper edges close, unless there is sand or fine silt which is likely to run into the tile, in which case the lower edges must be laid close, and the upper side cov- ered with clay or other suitable material. When, in making turns, or by reason of irregular-shaped tile, a crack of one-fourth inch or more is necessarily left, it must be securely covered with broken pieces of tile. Junctions with branch lines must be carefully and securely made. Blinding the Tile.; — After the tile have been laid and inspected by the person in charge of the work, they must be covered with clay to a depth of six inches, unless, in the judgment of the engineer, the tile are sufficiently firm, so that complete filling of the ditch may be made directly upon the tile. In no case must the tile be covered with sand without other material being first used. Risk during Construction. — The ditch contractor must assume all risks from storms and caving in of ditches, and when each drain is completed it must be free from sand and mud before it will be received and paid for l60 ENGINEERING FOR LAND DRAINAGE in full. In case it is found impracticable, by reason of bad weather or unlooked-for trouble in digging the ditch, or properly laying the tile, to complete the work at the time specified in the contract, the time may be extended as may be mutually agreed upon by employer and contractor. The contractor shall use all necessary precaution to secure his work from injury while he is constructing the drain. Tile to be Used. — Tile will be delivered on the ground convenient for the use of the contractor. No tile must be laid which are broken, or soft, or so badly out of shape that they cannot be well laid and make a good and satisfactory drain. Payments for Work. — Unless otherwise agreed, the contractor may at any time claim and receive from the employer seventy-five percent of the value of completed and accepted work at the price agreed upon in the con- tract. Tv/enty-five percent will be retained until the entire work contracted for is completed and accepted, at which time the whole amount due will be paid. Prosecution of Work. — The work must be pushed as fast as will be consistent with economy and good work- manship, and must not be left by the contractor for the purpose of working upon other contracts, except by permission and consent of the employer. All survey- stakes shall be preserved and every means taken to do the work in a first-class manner. Failure to Comply with Specifications. — In case the con- tractor shall fail to comply with the specifications, or refuse to correct faults in the work as soon as they are pointed out by the person in charge, the employer may declare the contract void, and the contractor, upon re- ceiving seventy-five percent of the value of completed drains at (he price agreed upon, shall release the work and the employer may let it to other parties. CONSTRUCTION OF TILE-DRAINS l6l Sub-letting Work. — The contractor shall not sublet any part of the work in such a way that he does not remain personally responsible, nor will any other party be recognized in the payment for work. Plans and Tools. — The contractor shall furnish all tools which are necessary to be used in digging the ditches, grading the bottom, and laying the tile. In case it is necessary to use curbing for ditches, or outside material for covering the tile where sand or slush is encountered, the employer shall furnish the same upon the ground convenient for use. All plans and figures furnished by the engineer, together with the drawings and explanations, shall be considered a part of the specifications. CHAPTER XII FLOW IN OPEN CHANNELS There are two classes of open channels required in draining land. These are ditches which are artificially constructed through swamps, level table lands without adequate natural drainage outlets, river bottom lands or salt marsh lands near the coast; and ditches which are made by enlarging, straightening, or otherwise improv- ing natural streams or watercourses in such a manner as to reclaim and sufficiently protect adjoining land. Velocity of Flow. As the velocity of the flow in such channels is an important factor in determining the size adequate for the work required of them, the engineer must be familiar with methods of computing it. The velocity of water in open channels is retarded by its contact with the bottom and sides of the ditch, the resistance being greater or less according to the nature of the material through which the channel is cut, and the irregularities in the surface of that part of the ditch which the water touches. The filaments of water from the bottom of the channel toward the surface, and from the sides toward the center of the channel form, respectively, vertical and hori- zontal curves, with the advanced portion of the curves in the center line of the stream. If these curves were plotted, the resistance of the sides and of the bottom of the ditch would have the appear- ance of holding back the water so that no two filaments would have the same velocity. The greatest velocity of the stream is found in that part of the thread of the 162 FLOW IN OPEN CHANNELS 163 current just underneath the surface, all other portions of the flow having a less velocity in proportion as they approach the bottom and sides of the channel. Velocity formulas give the mean velocity of flow for the channel, or, in other words, a single assumed uniform velocity which will give the same discharge as the several un- uniform ones which exist in the channel. In a trapezoidal channel the mean velocity is approximately eight- tenths of the surface velocity. This is found to be at a point in the center line of the stream about six-tenths of the distance from the bottom of the channel to the surface. The bottom velocity is from four-tenths to seven-tenths of the surface velocity, depending much upon the kind of material which forms the bottom and upon the size of the channel. Irregularities in bottom and sides of the channel, sharp bends and varying widths and depths modify the above general laws. Formulas for Flow. There is greater difficulty in correctly expressing by formula the velocity of flow in open channels than in pipes, since the character of the wet perimeter is more variable and the resistances of- fered by the sides and bottom change with the rise and fall of the water in the channel. The velocity is due to the slope of the surface of the water which in channels with free flow is usually parallel with and due to the grade of the bottom. This surface slope, however, is sometimes increased by the addition of volumes of water from tributary streams along the line. The Chezy formula, v = c\/rs, (4) is the general ex- pression for velocity in open channels now recognized by hydraulicians, where c = a variable coefficient, r = hydraulic radius = — = p wet perimeter s = slope = — = fall of water surface per unit of length. 164 ENGINEERING FOR LAND DRAINAGE Values for c may be substituted which will give cor- responding corrections for differences in velocity due to roughness of the channel. In Kutter's formula the method of determining c is substituted for c in the Chezy formula, thus: 1. 811 , , . .00281 , , .00281 1 + 41.6 H ; 1 + j-'+^}vrj \/rs . . (12) in which n = coefficient of roughness. Its value must be assumed and substituted in the equation. The por- tion of the formula inclosed in large braces gives the value of c in the Chezy formula. Value of n. No little uncertainty attends the selec- tion of the correct value of n for open channels, because of their variable character, so that at the best some margin for error should be allowed in the results. The factor n while called the coefficient of roughness of the bottom and sides of the channel, is applied in practice to obstructions of all kinds which retard the flow, and represents the correction necessitated by the fact that the velocity is not strictly proportionate to \ r s. Its value for open channels ranges between .02 and .05. Careful measurements have been made under the direc- tion of Drainage Investigations of the U. S. Dept. of Agriculture to determine the value of this factor for drainage ditches in alluvial and clay lands. Its \'alue for ditches 20 feet to 100 feet wide and 6 feet to 12 feet deep in fairly good condition is .028 to .03 and .035 for ditches in bad condition. Where ditches are in ex- ceptionally good condition, such as clean-cut clays or gravel, .0225 to .025 may be used. The following values of n are given in the hydraulic and excavation tables prepared by the U. S. Reclama- FLOW IN OPEN CHANNELS 1 65 tion service as approximately correct for the channels described. .020, Channels of fine gravel; canals in earth in good condition, lined with well-packed gravel, partly covered with sediment, and free from vegetation. .0225, Channels in earth in fair condition, lined with sediment and occasional patches of algae, or composed of loose gravel without vegetation. .025, Canals and rivers of fairly uniform cross-section, and slope in average condition. .030, Canals and rivers in poor condition with bed and banks par- tially covered with debris. •035, Canals and rivers in bad condition, channel strewn with stones and about one-third filled with vegetation. .040, Canals half-full of vegetation and with rough banks. On account of the tedious computations required in solving the equation for the value of c, short methods by means of tables or diagrams are commonly employed by engineers in finding the value of this coefficient. It is particularly desirable that necessary computation be as simple as possible consistent with reasonablj' accurate results. In order to facilitate the use of this formula, Table XI, giving the value of c for a wide range of drainage conditions in level areas, is inserted. To use the table, find r and the slope of the pro- posed ditch, then in the table which gives the slope nearest that of the ditch under consideration find the corresponding value of r; opposite this in the column headed by the values of n will be found the value of c, which is to be substituted in the formula. In case corresponding values of r and s are not found in the table the value of c can be interpolated with sufficient accuracy. i66 ENGINEERING FOR LAND DRAINAGE TABLE XI* Values of Coefficient c for Use in Kutter's Formula r Ft. n = Coefficient of Rougl)nes3 .017 .020 .025 .030 .035 .040 c c C c C c I 77 64 49 40 34 29 2 94 7g 62 51 44 38 3 104 88 71 59 50 44 S ^ I in 20.000 = .264 ft. 4 in 95 77 64 56 49 6 122 105 85 72 63 56 per mile 8 129 III 91 78 68 61 10 134 116 96 82 72 64 16 144 126 106 91 81 73 20 149 131 no 96 85 77 I 81 67 52 42 35 31 2 96 81 64 53 45 39 3 104 89 71 59 51 45 S = I in 4 III 94 76 64 55 49 10.000 = 6 119 102 84 71 61 54 .528 ft. per mile 8 124 107 88 75 66 59 10 128 III 92 78 69 62 IS I3S 118 98 85 ■75 68 20 139 122 102 89 79 71 I 83 69 54 44 37 32 2 97 82 64 S4 45 40 3 105 89 72 59 51 45 S = I in 4 III 94 76 63 55 48 S.ooo = 6 117 100 82 69 60 53 1.OS6 ft. per mile 8 122 105 !7 73 64 57 10 I2S 108 89 76 67 60 IS 131 113 95 82 72 65 20 134 117 98 85 76 68 I 85 70 55 45 37 32 2 98 !3 65 54 45 40 S = I in 3 105 89 71 59 51 45 2,500 = 4 no 94 76 63 55 48 2.1 12 ft. per mile 6 116 99 81 69 60 53 10 123 107 88 75 66 59 20 131 "S 96 83 73 66 * From Trautwine's Engineers' Pocket-Book. 1000 2000 DiscUarge In cu. ft. per s 3000 4000 140 130 120 110 100 FlO. 35. — DUGRAM FOR DeTERM 80 70 60 50 Stom width of Ditch, in feet, Side Slopes 1:1 THE Discharge of Open Ditches. FLOW IN OPEN CHANNELS 167 TABLE XL— Continued. r Ft n = I^oefficient of Roughness .C17 .C20 • ^25 .03 3 .C35 .040 I 86 71 56 45 38 33 3 98 83 66 54 46 40 S = I in 3 105 89 71 59 51 45 1,000 = S.28 ft. per mile 4 110 93 75 63 54 48 b 116 99 81 68 59 52 10 122 los 87 74 65 58 20 129 113 94 81 72 65 I 87 72 56 45 38 33 2 99 83 66 55 46 40 3 105 89 75 59 51 45 52.8 ft. 4 109 93 76 63 55 48 per mile 6 115 99 81 68 59 52 10 121 105 86 74 6S 58 20 128 112 93 80 71 64 Kutter's formula, while more elastic and better ad- apted to all classes of hydraulic problems than the more simple expressions which have a fixed coefficient of flow, c, depends largely for the accuracy of its results upon the values which may be given to the coefficient of roughness, n. That factor is more or less inde- terminate for ditches, so, as before remarked, some margin should be' allowed for error. It is the view of the author that in applying the coefficient of drainage a liberal margin between the computed capacity of a ditch and that which it may be called upon to carry should be allowed. Kutter's Formula — Diagram for Reading Discharge of Ditches Direct. Fig. 35 is a diagram prepared for reading without computations the discharge cf ditches with side slopes of i to i_ when bottom width, depth and gradient are known. The quantities are com- puted with n = .030, which has been found the general value which should be used for ditches in their average 1 68 ENGINEERING FOR LAND DRAINAGE condition. The diagram may be used as a general guide in designing the larger type of drainage canals. How to Use the Diagram. Find the bottom width of the ditch at the bottom of the diagram, interpolating by scale between number^; pass upward to the diagonal line which indicates the depth of the ditch; from this point of intersection, pass to the left until the diagonal line indicating the gradient or slope of thp surface of the water in the ditch is intersected; from that point, pass upward to the top and read the discharge in cubic feet per second. Should the capacity of ditches of smaller dimensions or with other values of n be desired, the necessary computations may be made with the assistance of Table 'XI for obtaining the values of c. It should be noted that in all cases the slope that the surface of the water will take when the ditch is in operation is the slope that should be used in the formula and in the diagram. Elliott's Formula. A more simple expression now known as Elliott's formula is one formerly used by English engineers, but modified by the author for use in the design of American drainage ditches. For ditches of ordinary size it gives about the same results as Kut- ter's with n = .0225. That coefficient has been found applicable to ditches whose perimeter is fairly clear of vegetation and other obstructions. In the design of ditches the author considers it good practice to use a medium drainage coefficient, and design the maximum flow of the ditches to be .8 of their depth at tlieir shallow section. This provides a factor to meet heavy storms and failure of the formula to represent the conditions of the ditch as they may affect the A-elocity. The simplicity and tested value of the formula when used as directed leads the author to retain it and recommend its use. FLOW IN OPEN CHANNELS IC9 ELLIOTT'S FORMULA V = -^ f X I.S h (13) Q = a V (5) in which V = mean velocity in feet per second a = area of waterway in square feet p = wet perimeter = length of bounding line of that part of the channel under water h = fall in feet per mile Q = discharge in cubic feet per second The number of acres which will be drained by a ditch is found by dividing the discharge in cubic feet per second by the runoff in cubic feet per second per acre. By formula the expression is, ' = § <-■> in which A = number of acres C = quantity taken from Table III If the area in square miles is required, divide Q by the runoff per square mile taken from the same table. Example : The bottom width of a ditch is 20 feet, general depth 8 feet, side slopes 1:1, and grade 3 feet per mile. How many acres will be drained by it, using the ^-inch drainage coefhcient? ' = V 4-5 X 4-5 = 4-S 769 ,8 depth = a = P = a _ P " 6.4 170.9 38 4-5 Q = 170.9 X 4-5 A = 769 7^7, .0105 170 ENGINEERING FOR LAND DRAINAGE The margin to be allowed between the surface of the water at maximum flow and the surface of the ground is subject to •topographical conditions. With fairly uniform ground surface throughout the length, one foot margin will ordinarily be sufficient. It should be observed, however, that the depth of flow should be controlled by the depth of ditch which can be obtained through the low land, irrespective of depths which may be safely permitted in other sections of the ditch. Relation of Depth to Mean Velocity. The effect of depth upon velocity in channels of the same width should be considered in the design of ditches, especially those having a light grade. Table XII shows these relations in a general way. Economy of construction and of subsequent maintenance as well as capacity are affected by these relations. TABLE Xn Mean Velocity of Water at Different Depths in Rectangular Ditch, 10 feet wide, Grade 3 feet per mile Depth in Ft. Mean Yd. Ft. per Sec. 0.5 1.4 i-5 2.3 2.0 2.6 2.5 2.8 3-0 2.9 4.0 3-2 5-0 3-4 6.0 3.6 8.0 3.8 It is seen here that the mean velocity in a channel of the above width, with water 8 feet deep, is 45% greater than when the water is only 2 feet deep. FLOW IN OPEN CHANNELS 171 TABLE XIII Relation of Width and Depth of Channel to Mean and Surface Velocity in Rectangular Channels b = width, d = depth, v = mean velocity, V = surface velocity. When b = 2d then v = .920 V " b = 3d " V = .910 V " b = 4d (( V = .896 V " b = sd " V = .882 V " b = 6d (( V = .864 V " b = 7d « V = .847 V " b = 8d u V = .826 V " b = gd n V = .805 V " b = lod (1 V = .780 V The mean velocity and discharge is greatest in pro- portion to the excavation when the width is twice the depth, and when the section of the ditch is a semicircle. CHAPTER XIII THE RUNOFF FROM LARGE AREAS The relation .of runoff to rainfall is an interesting as well as an important problem to the engineer. The value of water to the agriculturist demands that it be controlled, directed, and conserved in the most skil- ful and intelligent manner possible. A plentiful amount of the rainfall, which is unevenly distributed both in point of time and volume, must be stored in the soil for the nourishment of plants and supply of springs, yet a certain part must be promptly removed from the land by drainage, or injury will result in many ways. Rain disappears either as evaporation or runoff. The former term, as used in drainage discussions in distinction from runoff, refers not only to the water taken up by the atmosphere in the form of vapor, but is made to in- clude that drawn from the soil by plants in their growth, and also that which passing into the lower strata of the ground remains as bottom-water. The term runoff is applied to free water which passes from the land in various ways into streams. Evaporation. The rainfall can be accurately meas- ured by means of the rain-gage, and the runoff can be determined by continuous gagings of the streams which receive the drainage from a given area. The difference between the two amounts is evaporation as here used, and while the greater of the two, it can be known only after the amount of runoff has been ascertained. Precipitation occurs at intervals and in irregular quantities, but runoff is nearly continuous, and evapora- 172 THE RUNOFF FROM LARGE AREAS 1 73 tion entirely so. The latter goes on after drainage in any appreciable amount has for a time ceased, each growing plant drawing its water from the supply stored in the soil from rains occurring, perhaps, months before, but which has not been removed by drainage. Owing to this characteristic of soils, it is frequently shown by refined methods of measurements that for a short period evaporation is much greater than the rainfall for the same time. As a rule, it is least active when the demand for the drainage of land is greatest, because the humid state of the atmosphere during times of continuous precipitation checks the passage of vapor from the sur- face, and also because plants require less water from the soil at such times, owing to the supply of moisture which envelops their foliage. Though a most important agent in removing rainfall from the land, evaporation is so illusive when we attempt to assign to it a definite office in its relation to drainage that we are compelled to ignore it, and base our computations and con- clusions regarding the amount of water that should be removed by drains upon measurements of actual runoff from different kinds of lands under varied climatic conditions. Relation of Soil to Runoff. The condition of the land with reference to its ability to absorb and retain water is a much more certain and tangible element. This property permits the rapid reception and ample storage of rain so that in many instances a large pre- cipitation will be followed by little runoff until the soil becomes filled, when a large percent will, for a time, be delivered to the drains. Where lands have soils of dense clay or where the surface is rolling and com- paratively non-absorptive, the runoff is more rapid than it should be. In such cases efforts should be directed toward checking the surface flow and treating the land 174 ENGINEERING FOR LAND DRAINAGE SO that more water will be absorbed and stored for the use of vegetation. The distributing effect of soil, the relief afforded by surface depressions, and the time which is required for rain to reach the drains makes it possible to accomplish drainage with ditches which carry a small proportion 1' 1 1 1 1 1 1 1 1 ] ■ 1 a i ^ fi to s i 1 ' _i~ 1 , — 1 t iiS^lilBBiiii Days Open spaces, Rainfall Shaded " Runolf Fig. 36. — Rainfall and Runoff New Orleans Tract, December, 1909. of the rainfall. To the novice it seems hardly possible that drains with a capacity for removing one-half inch of water in 24 hours would furnish sufficient drainage for a tract when the precipitation upon it is two or more inches in the same time. We may state all of these truths in a general way, but cannot reduce them to figures which can be applied to the design of drainage works until we have some experiments relating to actual requirements under given conditions, upon which to base computations of the amount of runoff which should be provided for. THE RUNOFF FROM LARGE AREAS 175 Runoff Investigations. A study of the drainage needs of tracts as ascertained by careful examinations and measurements will enable the engineer to handle this phase of the subject successfully. Such a study should take into consideration all of the conditions which modify runoff in the particular locality which is ex- amined. The following reports of investigations along this line and deductions from the results will assist the - Q : w. __ ^ '_^ :: " ■ " *—* - - g - ~~:l'if,~; rt^Y~~^^fff — = (\ m^ '«vmk^. ^ ^ ^ >mi^. Wa Ww^Mm^/, |^ £ |^ ^ i^ ^ 1 11 21 Days Open snaccs, Kamfiatfl PhwluiL •< £uno« 31 Fig. 37. — Rainfall and Runoff New Orleans Tract, July 1910. engineer in determining the relation of drainage to rain- fall from the standpoint of benefits to land for agri- culture. The New Orleans Land Company's Tract near New Orleans, La.,* is a level tract of 1,085 acres, originally covered with cypress timber which is now largely cleared off. Its length is about double the width, and it is enclosed by levees and drained by two large canals which dis- charge at one corner over a measuring weir. Little of the land is cultivated, but mainly covered, instead, * Investigations by W. B. Gregory, A. M. Shaw, and C. W. Okey of Drainage Investigations, U. S. Department of Agriculture. 176 ENGINEERING FOR LAND DRAINAGE with a rank growth of weeds. Lateral ditches, which later will be required for complete drainage, have been constructed in but few instances. The runoff was measured continuously, with two exceptions, from q _ _ B ^ -- P 2 .... _. JB (y j3 n ' — E % K! Yi — n^^^^^^!7 W^^^^i^^mmdr- 1 11 -m. Days Open spacpB, 'Ratnf&'ll Shaded • ' RuuoiE 31 Fig. 38. — Rainfall and Runoff New Orleans Tract, March, 1911. June, 1909, to March, 191 1, by means of the weir and the rainfall was measured by a standard rain-gage. The records of three detached months have been selected to represent the relation of the drainage from that tract to the rainfall. The tabulated record which follows (Record No. 7) is also graphically arranged in Figs. 36, 37 and 38, to show this relation at a glance. These months arc fairly representative as to amounts THE RUNOFF FROM LARGE AREAS 177 RECORD NO. 7 New Orleans Land Company's Tract, Area 1085 Acres Runoff given in inches of depth in 24 hours Day Dec, 1909 July, 1910 March, 1911 RunofiE Rain Runoff Rain Runoff Rain I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 ■ 24 11 27 28 29 30 31 Ins. .018 .031 .051 .051 •055 •055 •055 .055 .065 .059 •059 .120 •337 •331 .320 .327 ■313 •259 .209 .206 .202 .198 .194 .191 .187 .184 .180 .177 .172 .168 .125 Ins. 1.74 ■■■.46' ■■■.65" 2.74 ".80" •33 .12 ■■■.48' .11 Ins. .047 .082 .136 •335 •309 .220 .178 .150 .122 .122 .116 .129 •237 .247 •179 •145 .122 .114 •342 .388 .291 .232 .194 .136 .120 .124 .117 .100 .ogo .072 Ins •OS •49 ■95 1.74 .14 '".66" •35 .40 •73 •71 •51 •73 il .92 •17 •37 .20 .10 .04 .04 .91 Ins. .035 •034 .032 .032 •033 •033 •033 •033 •032 •025 .019 .016 .oi6 .015 .014 .012 .012 .011 .014 .016 .015 .366 .623 •374 •374 •450 .380 •244 .174 •145 .114 Ins. .01 •23 3-8o ' Deductions and Comments Dec., 1909 July, 1910 Marcfi, 191 1 Total rainfall 7.43 in. 4^97 " •337 " 66.89 11.4 in. 5^36 " •387 " 4 47.02 S.i8in. 3^72 " .62 " 6 71.81 Total runoff Max. runoff in 24 hrs No. days that runoff was .3 inch or more for 24 hrs. . , Ratio of runoff to rainfall. . . 178 ENGINEERING FOR LAND DRAINAGE o 1 a oi < < o 1 NOO m -& rfi in 0\\0 i>ro ojVOvO ir)tN.|>N O M MOO '-•OVOVOOOOVO'OVO V}^ M 00 m M O iH 00 o vo in »o vo 00 « t~ ws m i> M 00 a M •* M vo m vo 00 •"I- •* Q oi'^M i>.rj w inoto o^*^ ^M low ffi ih 6\ ^ o6 Msd »0 IS •o so m 4 M IN fO ' f5 > o ■* 00 \o m tC. H vd ro IN W5 « 00 M f m in in M ■* ro in ' M « ■tS o 56\«M « oiniiM ■* vo m 00 M ^ •* p5 <^ in so n H \o vo ^ in N t>. ro N N ' •* IN ■ in a OvOmmOWOm'^IOOO J3 t; Oi m N ■^ in « M ■* " ■ fn in o\ H m m in in M •*oo fo ■>i-vd •d p! ^liefiod 4od ■*« >od •* w t* (S t* N ■* M 00 4 di 4 ■ in « r^ 01 n N ■* ■* IN in>o 4 m t^ m in ro ^■"i-^d inNvd ^^dvd i>-m j3 ^_^r<5« ininmn m Ot OtoqroMiHrooqo>- vo rj « « 06 M nj Oi « M fO 10 rp vO r* fo dv w dk £^ t^ ^ s oO'^oorjmooOMmin ^OMvoNinM'*MOin Sinrood 'NiiMOOTJ-vd ro w f»5 rj 00 •<*■ ro ro>d in t> o> in t^ n »^ Ov t^ t-i f*i in CO m di M in 1 o«inMmod»d4Hd\« m-s-^vdfoini-iMMto ^ s ^■^M M rOOO rpO\\0 fOvO o^diinind m ■<}--*Mvd fi ■ inod 0\ IH t^ m vo m oi •* en •♦00 ■* vd 00 ro vd CO M 1 in ■* M CO Ov vo 00 M 00 In CO Ov in pj t» cs (s H in H (s rs M i 5vO miniHoo ■ii-ininN m m ^ w5 m w in vo wj " * d •<}• t^ in cs (s m vo dv IN 4 CO vd 1 illliiiili M N 1*) 4 M M H M in vo ^. 05 6: 6 THE RUNOFF FROM LARGE AREAS 179 fS 5 52 ^§ J3 I^ fO fO CO w t- VO 00 HI v^ t» Ov P> 10 CO VO P« ■* >* 3 00 VO ro in % ■* VO Ov m w Tf ?? hi vd ro in 1> M in ■* m 5oo 5-S M 1> m m oi ro M 1> m t^ § ? Ov M t> VO 00 In CO CO VO 00 ■<1- PO 00 Ov t* m »— t r<5 eo N p» >J- m •* « « m ■* VO ro (S ■* ro VO M ■* > M 10 S" ■* Ov N ro VO 00 00 t» M Ov IN « 00 in t» VO 00 M Ov VO Ov VO VO 2; <«» c«5 " M fo in M HI N CO *^ PO HI Th CO u 00 ■* fO M •* M ^ M ro t« Ov m i> t- 00 m t* r< HI VO ■* 00 CS in 00 M Ov VO 00 Ov t> 00 C M M ■* M in « M CO Pf M HI m H M w -i-j f^ ro 00 ■* «5 ro 01 I^ VO Ov N Ov « 0, m VO CO t^ 00 CO VO ro 00 Ov M -vl- PO in j> 2 H « C m VO ■* M m CO CO VO CO cs HI tN m m bi vf^ VO m Ov M 1> <0 2 ^ H Ov CO M CO 00 CO 00 Ov Tl- 00 m 00 00 Ov 00 PI in w VO VO < c M VO ■* 1> VO « w) vO « •* m r( r> m po ■>t m m in >. t» VO in ■* m Ov t^ t^ in m VO t~ Ov CO M ^» Ov CO ■<*■ PO Ov PO 1—1 ■* i> m M VO M ■>!■ ■* 10 vO ■* HI t- 00 ,0 1> ■* H VO HI ?^ m VO Ov 1> « N Ov 00 t- 00 M VO VO M •* ■«■ VO Ov m J2 m Ov 00 m CO Ov Ov •* CO Ov 3 •—1 a «t m m m Ov 00 •* PO i> m ■* HI CO in !>■ 4 ■ M m >. VO N t~ VO VO VO Ov m Ov 00 m r) M HI Ov 00 VO m M H CO PO •*■ « tN t> t- PO I> p< ^ c M (S M 1> CO M in HI po M m 1-4 s vO 00 ? Th M Ov 0< 00 N J2 N 00 00 M 1> VO l^~ M M VO HI CO 00 m PO 00 M M c « n ro m fO m ■* ■ « ■* •* ■* HI ■* t> m « PO m xi ,r, M -rt- Ov ^ N 00 M Ov t^ 00 « Ov -v^ r^ 00 P« m p^ in r^ CO P) ^ ■* vO M m 01 c t» •vl- H M « n ■* VO N in in CO M M m M -vt •■^ •* d m i> i> 00 m f. Ov m M CO N M Ov t> ZS ^S; M 00 m PO m M VO in -i- *—> d ir> m (S H t» « W H N CO ■* t po VO r< pt t ■* k n •1 > 00 00 H H 00 M i 00 in VO Ov Ov 00 00 H (H 1> 00 Ov a 00 00 H M Ov CI 00 Ov HI M Ov Ov HI HI Ov M • ■ • ■ a in VO t« 00 ni lU Ov Ov ov ov kg HI H HI H ^ i8o ENGINEERING FOR LAND DRAINAGE " f "■ '" ■*■ "■ ~ — ■~ 7 _ 6 6 4 Ot m 4 vq 00 d 00 4 s ft 10 M q> d d fO M £ 4 H 00 d. 00 q 00 M M d q 4 8 M q m vq M 00 ro 00 M ro 00 N IN M m q CO ro fO M M M Ov 4 10 in w in M vq 1> ri M (S 4 & s H vd ^0 w M q\ 4 d. H in 00 r 00 M vd a < S 1- 00 10 q in in M in 4 m 4 fO fr M 1 00 vd £<>■ in 1> m M 4 10 00 m 4 4 d oc 4 10 M H H M CO ro 00 00 in VO ir M p; 4 s» M 10 00 IN M vq in IT q CO 1 m a 00 a H a M M Ov M M M a ^ 1 84 ENGINEERING FOR LAND DRAINAGE in shape, the Mississippi River levee forming one side and the pumps being located on the opposite side mid- way between the corners. The surface-slope is un- favorable for draining by pumps because the section RECORD WO. 11 Daily Rainfall and Corresponding Amount of Drainage Removed by Pumps from Willswood Plantation, St. Charles Parish, La., from June to October, 1909 * June July August September October Day Rain- fall Drain- age Rain- fall Drain- age Rain- fall Drain- age Rain- fall Drain- age Rain- faU Drain- age I Ins. o.is 4.10 I.OO Ins. 0.88 1.42 •76 •23 Ins. 0.12 .04 .02 Ins. Ins. o.s6 .48 Ins. Ins. Ins. Ins. Ins. z 0.20 3 5 6 •03 7 .63 .07 1.70 1. 12 0.3s 8 0.S3 9 .27 .10 .78 •22 •OS • IS .60 .68 .42 .30 .26 II 12 •2S .66 •49 .83 .26 0.16 13 1.40 O.IS IS .02 16 .OS 17 .32 .20 18 .20 •93 1.22 •43 .06 .40 .04 19 2.04 .96 .51 •43 •47 1.48 4.14 .30 1.03 .74 •34 .29 .20 21 22 .06 .14 23 I. II .10 24 .02 .18 25 .17 .19 26 .32 ■ 17 • 21 •SO .14 2.24 .70 27 28 .20 .27 .20 30 31 ..:::;..:;;: .09 Total 10.42 1 5.18 5-64 0.67 7.62 2.97 6.42 2.44 4.23 0.84 " From report of A. M. Shaw to Dept. of Agriculture. Drainage Investigations, U.S. THE RUNOFF FROM LARGE AREAS 185 RECORD NO. 12 Percent of Drainage to Rainfall, Same Tract * Month Rainfall, Drainage, Drainage Ins. Ins. % of Rain 10.43 S.18 49-6 S.64 .67 11.9 7.63 2.97 390 6.42 2.44 38.0 4.23 .84 19.9 June July August .... September . October. . . * From report of A. M. Shaw, Drainage Investigations, U. S. Dept. of Agriculture. next to the river levee has considerable slope, causing the water to flow to the pumps too rapidly. This taxes the capacity of the pumps severely in order to prevent injury of the lower land by the overflow of the ditches. The soil is receptive in character and the fields are drained by small open ditches 100 feet apart. Record No. 11 shows the daily rainfall and the amount of water in inches removed by the pumps each day from the entire tract, while Record No. 12 gives the relation of these. The data quoted show that at times when a 4-inch rain occurred the pumps removed in one instance 1.4 inch, and in another 1.03 inch in one day, but that or- dinarily the maximum was .7 to .8 inch. Were the land level, so that the water would distribute itself evenly throughout the system, it is probable that .75 inch would be about the proper coefficient. Boggy Bayou Tract, Desha Co., Ark. The surface of this 135,000 acre tract is nearly level and the soil heavy, underlaid with clay. The larger part is wooded and traversed by bayous and sloughs which bring the water into a small lake. A ditch was constructed from the lake four miles south to a point where there was a free discharge. The discharge of this ditch was measured i86 ENGINEERING FOR LAND DRAINAGE at the various heights of the water as read upon a gage, and a rating curve constructed. During April, 191 1, the rainfall amounted to 13.72 inches, which is the largest ~ "~ ~ "" ~ " ^ 1 1 1 1 1 ~i i 1 1 'III 1 ' 1 _ — tl r.. B 1 m 2 •^ M 1 1 1 1 ! 1 1 1 1 1 j: 1 1 ■ 1 - 1 ■ -1 - - _ ^ U- •] p 1 t"" : : i - s - : ; 7. P ^ fff ^ :7 , s - z ^ ^ 5 ^ - L- n = WX: i i s i @ 1 S L i; t 3 td IL Open spaces, Raiiifull fijuuled " Ruiioll: Days ao Fig. 40. — Rainfall and Runoff Boggy Bayou, April, 1911. precipitation recorded for any one month for the last 17 years. Record No. 13 gives the rainfall as it occurred, THE RUNOFF FROM LARGE AREAS 187 RECORD NO. 13 Boggy Bayou Tract, Desha Co., Ark. 135,000 Acres. Rainfall and Runoff for April, 191 1 * I . 2. 3 4- 5- 6. 7- 8. 9 10. II . 12. 13 14 IS- 16. 17- 18. 19- 20. 21 . 22. 23 24. 2S. 26. 27- 28. 29. 30. Total . Rainfall, Ins. 5.60 .04 .10 .40 1.36 .08 .96 .02 .48 3-20 .88 .56 .04 13-72 Height of Gage, Ft. 131-6 .0379 130.9 .0291 130.3 .0220 137-9 .2070 138.7 .320 138.7 .320 138.6 .282 138.S .264 138.4 •247 138.3 .238 138.3 .238 138.3 .238 138.2 .229 138.0 .213 137-9 .207 137-8 .201 137-6 .192 137-S .187 138.3 .238 138.4 -247 138.4 .247 138.3 .238 138.1 .220 138.1 .220 137-9 .207 137-7 .196 137-4 .183 137-0 .166 136.4 -14s 135-S .119 Depth of Run- o^, Ins. 6.098 * From report of D. L. Yarnell, Drainage Investigations, U. S. Dept. Agriculture. 1 88 ENGINEERING FOR LAND DRAINAGE the height of the water on the gage, and the corre- sponding daily runoff for the entire area. It should be understood that the ditch merely takes the overflow from 135,000 acres which has but little natural drain- age. The rains of April 4th and 5th caused a rise of 8.4 feet in the water of the ditch, due largely to drain- age which came to it from near-by territory, and taxed the ditch to its full capacity. From that time on, large volumes flowed away through the flat country into another bayou so that the record shows a maximum runoff of only .32 inch per day. The actual total run- off was estimated at not less than .6 inch. The record shows conditions of flow from a large level area which has but few drainage channels and for which the outlet is not sufficient. It is represented graphically in Fig. 40. Vermillion River Drainage District, Livingston Co., Illinois.* This is a level table-land of 128,000 acres, lying at the head of Vermillion River, and forming the upper part of its watershed. The entire drainage is ac- complished by a system of artificial ditches from 8 ft. to 70 ft. wide, the farms for which they serve as outlets being drained by tile. The area represents a well- drained level portion of the State, so that the data relating to the operation and effect of outlet-ditches may be taken as a guide for draining that class of lands. The rainfall and runoff for this district is given in Record No. 14, and represented graphically in Fig. 41. The rainfall for May was greater than that of any one month during the ten previous years, with the excep- tion of June, 1902, so that the amount recorded may be regarded as the maximum discharge which will be required of the outlet in that part of the State. * From report of runoff from drained areas in Illinois and Iowa, by L. L. Hidinger, Drainage Investigations, U. S. Dcpt. of Agri- culture. THE RUNOFF FROM LARGE AREAS 189 RECORD NO. 14 Vermillion River Drainage District, 128,000 Acres. Rainfall and Runoff in May, 1908 1 . 2 . 3- 4- S- 6. 7- 8. 9 10. 11 . 12 . 13- 14- IS- i6. 17- 18. 19- 20. 21 . 22 . 23- 24. 25- 26. 27- 28. 29- 30. 31- Date Total. Rainfall. Ins. ■05 •03 1.26 •SO .09 .60 .10 .06 •S5 1. 61 .40 •54 •87 .46 .40 •IS .40 •63 '8.72 Gage Height, Ft. 7-oS 6.02 6.00 6.1S 8.03 10.05 10.70 "•45 12.00 1 1. OS 9.70 9.70 10.70 11.65 11.90 10.80 9.90 9-75 10.4s 10.95 10.40 9-65 8.50 6.05 4.90 4^15 4.40 S-iS S-70 6.20 6.20 [Runoff Depth, Ins. .082 .064 .060 .063 .132 .224 .276 •336 .380 •304 .206 .206 •273 •352 •372 .282 .222 .210 .256 .296 .252 .202 .140 .061 .038 •023 .028 .043 .•054 .064 .064 5-562 For annual rainfall in Illinois see Record No. 3. iqo ENGINEERING FOR LAND DRAINAGE A number of districts in the drained portion of the State have been examined in a similar manner, and from the results which are obtained a curve has been constructed to represent the relation and amount of run- off to districts of different areas in that section. (Fig. 43.) It should be noted that the ditches in the smaller areas do not, in many instances, run full, as it is desir- able to keep the flood-plane of the ditches considerably 1 _ _ --U U ^1— - VnvA>. Mmw^'^'^ViV-'-- 11 Open spaces, Rainfall Shaded » RunoC 21 Days Fig. 41. — Rainfall and Runoff Vermillion River District, May, 1908. below the surface of the land so that the tile-drains which discharge into them may operate without seri- ous interruption. For this reason the trend of good practice is to make the ditches of such capacity that the level of ordinary flood-flow will not reach the top of the ditch. Relation of Drainage Coefficient to Area. In general, the drainage coefficient is largest for small areas and diminishes as the areas increase, in a ratio dependent upon the topography of the watershed and the amount and duration of precipitation on its several parts. In the reclamation of bottom-lands adjacent to THE RUNOFF FROM LARGE AREAS I9I Streams which are subject to overflow, the volume of water must be estimated by gagings or by comparing them with other streams whose watersheds and dis- charges are approximately known. The runoff from hilly sections is so far different from the more level sections that each valley must become the subject of a special examination. Record No. iSi showing the flood runoff from some re- presentative streams in the Middle West and the South, indicates the general range of maximum discharge from the streams named. The topography of the watershed of each stream and also the season of the year when the measurement occurred should be noted. How to Select the Drainage Coefficient. Summing up the matter contained in the foregoing discussion, the engineer should take under consideration the fol- lowing factors and conditions when selecting the drainage coefificient for a new district which is to be drained. First, rainfall and temperature. Localities which have a large annual rainfall usually have a correspond- ingly large precipitation during one or two months, and those months have large 24- and 48-hour storm periods. It is during such periods that the greatest capacity for ditches is required. Lands in warm cli- mates require as large drainage channels in proportion to rainfall as those in cold climates where the surface and soil are similar. While the total annual runoff in the former is not so great as in the latter, because of increased evaporation during part of the year, the requirements of ditches in order to meet the demands of storm periods are not essentially different. Second, topography of the area. Level areas require smaller coefficients than those which are undulating and hilly, because the land absorbs more water and 192 ENGINEERING FOR LAND DRAINAGE ■a u -&> "3 v O Si (U •9« £ la a> ll A S5i & ^ 3 •o5 «« o ig ia •S in •a o _g CO a 00 in inn o> ri H N d lo + + + + + d o six. ■ScJ CO a; 00 H o ■*3- t^H o>oo^ voovd ^d ^ Oi Ov O ^00 ++++++ Oi^oo «oq ro M vdvdvd £^ inoitooo ^ H N in ++++ o H r^ mm CO PO cs « w ro o o M ^^ ^ ^ M M Iks Si a •3 iS (A 00 t^I^ tH « O M M Ol>0 PO PO *'0 n ^ 2§ S: rj OS •? S O S-S Son R 5 g o lu ^ £ g us r = o o M o o o o o o o o o o r>o o o o o *o o o. >" ^ i>oo 00 d' ^ ff i»oo ^« ^ « ^ o ej >* in o 00 >o" in rT m *>d" •3 d 3s" " ■ 5- 4)- - - m o tH n o o o o o o mo o t-p« ►Too m"oo»C < t~o o o r» 0*0 m Ok ro o oim^oo ro M M M o « M fO CO CO ■ Js- - S2.S' 2=1 3 o SOS ba C a a J2 SI ■q. S a np< THE RUNOFF FROM LARGE AREAS 193. gggg &vg> ++ + + n M M H ++++ o m^O ■* M In o In M "^fOlNrj fCO\£^ in -^ tCio w M H ci +++++I ++ + o O - *j M 1-. 3 s oj dj o OVO (S H 00 o vO Ot 0\ 10 in •* in ro ^ ^ « ■^qvin^M e>rj 06 t^ d d in n ^in 3 a oj (u o O M M w N PO ro vo 1/) N o o 10 -^00 ? M O O « 0000000 o\ Ot ot o H M Oi Ot O N OiOO CO t< oooooooin •^mnm moo vo 00 H^ IN O 'J t; In O 00 ^d* tC In o f^o" «" rT ^-o M ^» oovo vd" fo o Oi ■* ■*« o o in ■* M ovc~co t. H^ «^ t^ q^ Tf >j w^ rOOOOfOOOPO VO 0\ N O O O OivO M_oo in O; M Ovoo M VO « PO 1= 3 S ^ 3 0.3 s^^ s a u =5 01; «3 s : (14 en „ o S- i ^= = (II s O 0) eS ^ M ? :=i :-C sn-S 2-a a m 2 w-a S go Si o •M 2. . a= a-' 194 ENGINEERING FOR LAND DRAINAGE aj V a I 3 y OJ D O + + + + + + fS 00 1> o MOO Tt-lO ?.g OiOO -^lO t» N Tf 00 f 00 M o O 00"0 t^o t* M ir> Ot 10V0 pt ^ •H r» lo ^ "^ !>■ O* O ^ M 00 O 'O l> U U en OJ o o o o M lO Tf f 00 t-OO M o o in Oi 00 m p« o o o o o o in in •* o ^ o t^ o 00 "O^ o^ o^ in O; ^ ^ oi f^ i^ o'oo' t^ (^ n ot M r«) M m o o o « o o o o t^ w00»O VOOO t^oo ro OvOO 0\ Oi Ot ■* fO ^ M rooo m o m i-i o n oco O H mSmS Sw> ^ SS(S 3 3»!j 3- 3 (Z| s- 5S = ra C8; S O O « 3m 5a S 3-9 all' all d v II (»P4 ta 9i vi s So THE RUNOFF FROM LARGE AREAS 195 11 dJ C CO y > ^ « in M M + + + moo 00 in t^m in CO *+ ++ + VO O ^ + + + Os lOvO ro OvOO t^ m in o*^ 10 ■^(swinMooMt^ •So 000 ro^»mt^m^^ N roHOO rOM (S Osi>0 OlOtS 0\0"0 ■ po w o vo m ^ o\ ■ PO "^00 CO POOO M moooooot^OMOO CO fotH mo^o po^'tooo poo -^vd* m" ino" PO lo^o" t-T 10 -^ d" N'O'^l-lirjHIH H fO lOOOlONOOO M popoO\ininON^ 000 t^d\^ « PO^O O O 00 00 O O ThO -"t ■* w Tf Tfo r^oo ovo ■^0100 POO\ ■^lOPi o\po»ninooo\o m« O 000 -^O tn o M "^ o o M mo o vo 0'*;iON H q^O\J> M"in o flljjllg 3 (S iS 3^S 0) o m "! fi o 3i «; •9c«'3-j'-!giSP ■n S OS- es 3- - US H 196 ENGINEERING FOR LAND DRAINAGE the movement of the latter through the soil and over the surface is slower and more uniform. Third, size and shape. In general, the ratio of drain- age to rainfall is less for large areas than for small, be- cause the rain may not be uniform over the whole; because more time is required for water to reach the main channel from the more distant parts so that the flood portion of a part of the territory may have passed off before the other part arrives; and because a larger part passes away in evaporation. The ratio is greater from long and narrow districts than from broad ones, since the water finds its way to the channel quickly from each side. The topography may materially modi- fy these conditions. If the land at the upper portion of the district is comparatively level and that at the lower is hilly, the crest of flow, after a heavy precipita- tion, will pass from the lower before that from the upper arrives. This is not true, however, when long periods of precipitation occur. Fourth, character and culture of the land. Undulat- ing or rolling lands which have a hard and smooth sur- face, like meadows and pastures, give a larger runoff than cultivated fields. If hilly lands are terraced or underdrained so as to conserve a part of the water and distribute the surplus evenly down the slope, the drain- age coefficient will be less than if no care in that regard is exercised. After the above points have been determined, com- pare districts which most nearly resemble the one under consideration whose drainage runoff has been ascertained, and select a coefficient for computing the size of the outlet ditch. Consider the several large sections of the whole separately with respect to the amount of runofT and the manner in which it is brought to the main, and adjust the tributary ditches to the esti- THE RUNOFF FROM LARGE AREAS 197 mated runoff of the several parts. The distributing effect of time in the movement of the water to the main, and the area of each section, should receive their proper weight. Drainage Curves. The foregoing discussion of run- off measurements suggests that the relation between the areas and the amount of drainage they require may be expressed graphically by a curve. This could be done for any given section with reasonable accuracy, pro- vided measurements could be made for a series of years at different points in the area. The data re- quired to construct such a curve are the area drained by a single channel, the record of rainfall, and measure- ments of actual discharge at different points along the channel where the drainage of a known part of the whole must pass. The discharge from the correspond- ing areas may then be plotted to a scale and a curve made to pass through three or more of the points. Fig. 42 represents a curve constructed for areas rang- ing from 4 to 200 square miles. The data were col- lected from different level areas in the north Mississippi Valley, which have absorptive and easily drained soils. It does not represent the runoff conditions of rolling lands, but from level lands which are well provided with drains. The smaller area requires much the larger relative capacity of drainage ditches to meet the needs of farm land, as, for example, the drainage coefficient is yi inch for 4 square miles and % inch for 40 square miles. As has been noted, the drainage coefficient for small areas in the same section which are well tile- drained is about yi inch on account of the large storage capacity made possible by this method of draining. Fig. 43 represents data collected on areas in north central Illinois for maximum runoff. Curve A repre- sents the drainage from 200 square miles and lesser 198 ENGINEERING FOR LAND DRAINAGE areas in the same part of the State. The upper part of the curve represents the capacity of the ditches which have been constructed instead of the amount of drain- gjiui ajunbs isd pnoaas .lod Taaj ojqno nj go-nnH 1 r . It 1; 9 1/ s 3 i 3 CURVE 8H0W[N0 RUN-OFF TO BE PROVIDED FOR BY DRAINAGE DITCHES IN SWAMP AND OTHER WET LANDS OF THE UPPER MISSISSIPPI VALLEY, C =Rim-«ir in on. ft. per sec. per sq. mllo. M=Dr»inngo areii.iiL.Ml. miles 0=^+3.03 3 ;/ g s c S = II s II "1 « = 1 1 d 1/ > 1 M / n 3 V § y ~ x= ■^- — '« T 1 ^ #';= notn ■m-a < OJ "HI 5^ Idcic t ^> ^ age, since they are the outlets for tile systems where it is desired that the ditches never run full. Curve B more nearly represents the flood capacity required for satisfactory drainage. THE RUNOFF FROM LARGE AREAS 199 It seems evident that each different area has its own drainage curve and, further, that this will take vary- ing forms under different climatic conditions, and that o > a s U a o < g Q it will be modified by surface changes incident to the development of a country. For example, the runoff from a country through natural watercourses only is represented by a curve which more nearly approaches a 200 ENGINEERING FOR LAND DRAINAGE Straight line than one drained by a well-arranged sys- tem of artificial ditches. Greater precipitation requires greater drainage Capa- city where the conditions in other respects are the same, but the law of flow is similar. For this reason data which are particularly adapted to one section will be helpful to the engineer in planning drains for another, if he gives due weight to the diflferences between the two. CHAPTER XIV LOCATION AND CONSTRUCTION OF OPEN DITCHES With the preliminary work done, its results con- sidered, and a suitable plan of drainage adopted and outlined upon the map, the engineer is ready for laying out the system upon the ground. The survey for a ditch, after an approximate location, consists of staking the center line, locating it with refer- ence to property boundaries, and taking levels from which the grade and amount of excavation can be com- puted. It may begin at either the upper or lower end, the latter usually being preferable. Where State drain- age laws specify the place of beginning and manner of staking, the method prescribed should, of course, be followed in those States. Staking the Line. Ditches and drains pertain to the land through which they pass, and the center line should be tied by measurements to the property lines, the length of ditch on each property being indicated on the final map. Start from the initial point and run the line with either compass or transit, measuring it with field steel tape or chain, and setting temporary stakes at each 100 feet, numbered consecutively. If the ground is level, as in swamps, river bottoms, etc., also set on the center line permanent stakes with hubs at 300 feet in- tervals, and at intermediate points where the line changes direction, or where property lines are inter- sected, the distance from these points to the nearest 202 ENGINEERING FOR LAND DRAINAGE property corner being measured and noted. These measurements will prove important later in adjusting assessments for benefits and damages. It is more essen- tial that the location of the ditch with reference to property lines and corners be represented than that the azimuth of the line or its magnetic bearing be cor- rectly ascertained. Levels should be referred to the datum established for the district in the preliminary survey, and the entire system of elevations should be carefully checked as the work proceeds. If the district is large there may be a location party, with level party following, thus hastening the engi- neering work. When it is practicable, the entire instru- ment wck connected with the location should be done by the same engineer, who should also be the one to establish the grade. A personal familiarity with the ground along which the line runs is of great assistance in designing drainage works, and in the ready interpre- tation of survey notes. Bench-marks should be estab- lished at convenient points about 75 feet from the line, for use in testing the grade of the ditch after its com- pletion or for continuing levels elsewhere in the district. These should be definitely marked and clearly described in the notes and a liberal number of them should appear on the map and also upon the profile. A convenient method of designating bench-marks is to number them consecutively as B M No. i, B M No. 2, etc., in connection with the correct elevation of each; and if there are two or more instrument men, the initials of the one setting the B M should appear on it also. These, as well as the numbers of the center stakes, should be marked with red keel pencils. Establishing the Grade. Where the land is level and the general topography is simple, the grade of the ditch can be run in on the field-book and the depths LOCATION AND CONSTRUCTION OF OPEN DITCHES 20T, and the excavation be computed direct, but the bet- ter way is to reduce the level-notes to profile form and determine the grade-line as directed in Chap. VI. If the center line does not represent the general surface of the land, the true surface-line should also be plotted, so that its relation to the grade-line may be seen. To decide what will constitute a satisfactory grade involves a consideration not only of the requirements of the ditch, but also of the nature of the earth. Grades are limited by nature and we can only adjust and use them. The most essential part of the work is to get an outlet and such depth as will serve the land through which the ditches pass. The grade should then be made as uniform as practicable, and may be as small as 6 inches to 12 inches per mile for gravity ditches, and o to 3 inches per mile for ditches used in draining by pumps. Ditches with grades not exceeding 3 feet per mile can be kept in repair more cheaply than those with steeper grades because the banks are not injured by erosion and the velocity of the water is sufficient to make them at least partially self-cleaning. Depth of Ditches. The topography of the land through which a ditch passes naturally governs largely the depth it shall have. For efficiency and economy of construction, ditches from 6 to 12 feet deep are desirable. The former, if sand and gravel are found in the bottom, and the latter in lands with clay subsoil. The con- struction of ditches exceeding 12 feet in depth is quite often attended with difficulty and additional expense, and should not be recommended until a thorough ex- amination of ,the earth has been made by borings, so that the material to be encountered can be safely predicted. There are limitations to depth which are 204 ENGINEERING FOR LAND DRAINAGE dependent upon efficiency, first cost, and maintenance, that should be first determined for the area. Computing the Size. Ascertain the total area to be drained in either acres or square miles; multiply this area by the runoff in second feet corresponding to the drainage coefficient for the area selected from Table III. The result will be the number of cubic feet per second which the channel will be required to discharge at the outlet. Assume a channel of estimated section, the grade and depth having been previously determined, and compute its discharge by substituting the proper values in Kutter's formula (No. 12) or Elliott's formula (No. 13). When Kutter's is used, it should be observed that the result obtained will vary greatly according to the value of n which may be selected. If the value of Q for the ditch of the assumed size does not cor- respond to the required discharge, the size should be increased or diminished until the required capacity is obtained. In a similar manner the cross-section at various other points along the channel should be computed, particu- larly where there are material changes in grade or where large branches or tributary streams enter. Good judg- ment should be exercised in adjusting the size of ditches to diflferent parts of the area, since physical conditions of surface and soil should be taken into consideration, and also the fact that the drainage coefficient does not provide for unusual storms which occur at long inter- vals in some localities. Illustrative Example. A level district of 50 square miles is to be drained through one channel 8 feet deep, with grade of one foot per mile. If the channel has side slopes of >^ to i what should be the bottom width at the outlet when a drainage coefficient of yi inch is used? LOCATION AND CONSTRUCTION OF OPEN DITCHES 205 13.44 sec. feet X 50 = 672 sec. feet = required value of Q. Assume a bottom 25 feet wide. Work by Kutter's formula (No. 12). a = 232 P = 43 r a = - = S.40 n c = .025 = 80 s = 1.056 ft. per mi. = 8oJ?3?X.o \ 43 ,0002 = 2.63 Q = 232 X 2.63 = 610 sec. ft. In a similar manner, computing the discharge of a ditch with bottom 28 feet wide we would get a result of 686 cu. ft., which nearly meets the required conditions. If it is not desired to have the channel flow full at ordi- nary flood times it will be best to use a ditch with 30 ft. bottom. Should we use .0225 as a value for n, which would be about the right factor if the channel were in clay land and kept in good condition, the discharge of the ditch with 25 ft. bottom would be 675 sec. -ft., or the amount required for the area. The trial method is used because the formula be- comes too unwieldy if arranged to give size of channel direct. Taking up the same problem and working it by El- liott's formula (No. 13), we have the following: a = 232 I ^ ~ p = 43 ' = -vr:^ ^ '-58 = ^-52 t}4h = 1.58 \ 43 Q =677 Assuming that while we have a ditch 8 feet deep we wish to have the maximum flow only .8 of the depth of the channel, and computing the trial channel with 30 ft. bottom, and depth of flow 6.4 feet, we have the following : a = 212 i>^ h = 1.58 \ 44-3 Q = 212 X 2.7s = 583 I 233 X 44-3 206 ENGINEERING FOR LAND DRAINAGE A ditch of such capacity would carry the water at a permanently lower level than the others, and would also provide for an unusual flood flow. Side Slopes. The liability of earth to slump or slip in many localities where ditches are to be made, makes it necessary to construct them sometimes with side slopes as flat as I>^ to I, or 2 to I to make them per- manent. The other alternative is to make the excava- tion large enough to permit the sides to cave and take their ultimate slope, and leave a clear ditch of the speci- fied size. The latter is, perhaps, the more economical method to pursue if one can predict the behavior of the 16.0 Fig. 4<. — Side-slopes ^ to i. earth after it is excavated. The superiority of a slope constructed as it is desired to have it remain cannot be denied, and it should be so made if it is practicable. Slopes as ordinarily constructed by the floating dredge are >^ to i or nearly vertical, as shown in Fig. 44. Stiff clays stand well at that slope and lands which are some- what loose in structure do not cave badly unless the ditches are deep. The engineer should make sufficient examination by borings or otherwise, to enable him to determine what slope of banks should be specified. Berm. A wide berm will lessen the risk of caving banks since the earth of the waste banks is deposited at such a distance from the ditch that their weight will LOCATION AND CONSTRUCTION OF OPEN DITCHES 207 not cause the sides of the ditch to be displaced. Ordi- narily a clear berm of lo feet between the edge of the ditch and the foot of the waste bank is sufficient. If the excavation is made through a soft marsh, a greater distance may be found necessary. Dimensions of Small Ditches. Another factor be- sides carrying capacity enters into the design of the size of small outlet ditches, and that is their economic construction and subsequent maintenance. A mini- mum bottom width of 4 feet, or of 3 feet where the grade exceeds 4 feet per mile, is approximately correct, depending much upon climate and earth conditions. The reasons for such limitations are as follows. It is impracticable to make ditches with narrower bottoms or to clean them out except by hand labor. This should always be avoided as far as possible. The continual silting of ditches on light grades is a contingency that must be recognized in their maintenance. An amount of silt or the caving of the sides which would place a barrier a foot deep across an 18-inch bottom would cause little injury to a four-foot bottom, and could be removed more easily. There is a noticeable difference in this regard between ditches in cold and those in warm climates. Alternate freezing and thawing causes the sides of ditches to crumble and slough off, thereby materially contributing to the silt deposit which tends to obstruct the flow in small ditches. This is not the case in southern climates, so that we find the ditches in many instances maintain- ing almost vertical sides, and silting is due to water action alone. As a matter of economy in land surface, cost of construction and efficiency of operation, ditches should have as steep side slopes as can be maintained. For the same reason the waste banks which are often left rough and become covered with useless vegetation 208 ENGINEERING FOR LAND DRAINAGE should be leveled and utilized, with the exception of a narrow border of 3 feet on each bank, which should be laid in grass to keep the banks intact. These features should be considered by the engineer since they are im- portant in the design and construction of the smaller outlet drainage works. • In passing, it may be suggested that large tile drains may, in many cases, be substituted for such ditches. Cross- Sectioning. If the ground is a plane surface, quite uniformly level, center line elevations are suffi- 20.8' 14.0' ^'-'"-yw** ,0^^ ^ i^— J / ". W* eo >^ 1 6.0'\^ 8.0' 1 8.0' / 12.8' 16.0' Graae ELIM.O Fig. 45. — Setting Slope-stakes. cient for computing the excavation, with hubs at the points mentioned under Staking the Line. The top width can be set off from the center stake by direct measure- ment, and marked on either side by stakes called slope- stakes. If the side slopes are i horizontal to i vertical the distance out on either side of the center is yi the bottom width plus the depth; if i.J< to i, it is >^ the bottom width plus \]4 times the depth, etc., or, in general, one half the bottom width plus the product of the depth l^y the rate of slope. When the ground is uneven, a method called cross- sectioning must be resorted to for determining the position of slope-stakes, and securing measurements for LOCATION AND CONSTRUCTION OF OPEN DITCHES 209 computing excavation. The process is as follows: The grade elevation at each station having been deter- mined and entered in the field-book, set up the level at a convenient point for taking observations on several stations. Obtain height of instrument from nearest bench. Have the rod set at an estimated distance out as a, Fig. 45 ; find elevation, and from it subtract the grade elevation which in the example is 109.0. If the side slope is i to i the distance out will be 8 + 12.8 = 20.8. The rodman, with the end of tape at c, measures the distance c a. If if is 20.8, the stake is driven and the 17.0' , 16.0' Grade EI. lO&.O Fig. 46. — Slope-stakes on Uneven Ground. distance and cut are recorded in the notes. If not, another trial should be made. The rodman then esti- mates the elevation at b, a level is taken, and the dis- tance from c determined in the same manner as that for a. In the example, the elevation of b = 115.0 and the depth atb = 6. cb=84-6 = 14.0. Whatever the side slopes may be, the same method is employed, observ- ing the rule before given for computing top width. If an allowance is to be made for an old ditch or channel which will necessitate a deduction in computing excava- tion, levels should be taken at e and f. Fig. 46, so that the sectional area of the existing channel can be com- puted and deducted from the whole section. The slope 2IO ENGINEERING FOR LAND DRAINAG Stakes having been set, the contractor may begin at the limit indicated by them and extend the required slope to the depth indicated on the center stake, which will give the ditch the bottom width that has been designated. Keeping Cross-Section Notes. In order that the notes from which excavation is to be computed be kept free from all possibility of confusion, the elevation of each station on the center-line and that of the grade-line should be transferred to another page of the field-book, and headed Cross-Section of Drain No. — from Sta. — to Sta. — The form is arranged for recording the elevation of the ground at each slope-stake, indicated as Right and Left as the survey proceeds up grade, the distance of each from the center, and the number of cubic yards of excavation when the computation has been made. FORM FOR CROSS-SECTION BOOK. (Left-hand page.) Sta -s Elev GL C Cut R Cut L Cut DiST. Ol-t Cu. Yds. R L 21 R L 1 126.2 [ 4.4 II.2 1 17.0 I2I.8 115.0 109.0 8.0 12.8 6.0 20.8 14.0 R L The computations for obtaining the height of instrument are made on the right-hand page of the book, since the H I may be obtained by taking a backsight on the bench- mark or center stake, whicliever is most convenient. Computing Excavation. The usual method of com- puting fxcavudon for ditches is by end areas, which is as follows: Add the end areas of any given section, di- vide by two and obtain as a result the mean area. LOCATION AND CONSTRUCTION OF OPEN DITCHES 211 Multiply this result by the length of the section and divide by 27; the result will be the number of cubic yards in the station. There are many tables and dia- grams in use which greatly expedite and lessen the labor of such computation. The following Excavation and Embankment Table (Table Xiv) is regarded by the author as having a more general application to the work of the drainage engineer than many others. It is adapted to general use in all classes of ditch and levee work. It gives the number of cubic yards in a sta- tion of 100 feet when the mean cross-sectional area is known. To use the table proceed as follows: Having the mean end area, turn to the column headed Area in feet, and find the corresponding number. Opposite this will be found the number of cubic yards in a length of 100 feet. If the area has a decimal part pass the eye to the right and take the number of yards in the column under the decimal corresponding to the one required. If the number of yards for only a part of a station is required, take such a part of the tabular number given as the required length is of 100 feet. Illustrative examples. The mean area of a loo-ft. section is 133. How many cubic yards of excavation are required? Find 133 in the left-hand column and opposite under the o column is 492.59, the number of cubic yards. Suppose the mean area of a 100 ft. section is 119.6. Find 119 in the left-hand column, pass to the right, and in the column headed .6 will be found 442.96, the number of cubic yards. To find the yardage for areas larger than those given in the table, find the cubic yards for half the required area and multiply by two. Example- — If the mean area is 642.4, the cubic yards will be the number corresponding to 321.2 (1189.63) multiplied by 2 = 2379.26 = cubic yards required. 212 ENGINEERING FOR LAND DRAINAGE Another method of using the table when the areas are larger than those provided for by the table, and do not exceed 3599, is the following: Point off one place from the whole number as decimal and find the cubic yards for that number; then remove the decimal point one place to the right ; the result is the number of yards re- quired. If there is a fraction, find from the table the number of yards in the fraction and add it to the yard- age obtained from the whole number area. Taking the above example 642.4 and removing the decimal point one place to the left, we have 64.2 ; the number of yards correspond- ing to this area is 237.78. Removing the point one place to the right we have 2377.8. Adding to this 1.48 the nmnber of yards corre- sponding to .4, we have 2379.28 cubic yards. As the several stations are computed, enter the re- sults in the note-book opposite the respective station in the column headed for that use. Right of Way. Crossing public highways and rail- roads often delays the progress of the work because of failure to make necessary and timely arrangements with the authorities who control the respective rights of way. Highway bridges along the line must be removed in advance, and replaced after the channel has been exca- vated. This is done by the contractor at the expense of the district in some States, and by the county road authorities in others. Facilities for securing the proper grade should be given the contractor at such places, so that he will make no mistake, and the earth should be deposited where it will best accommodate the interests of the highway. In crossing railroad rights of way there must be cor- dial cooperation between onpinccr, contractor, and rail- road company, for while the latter must guard its important traffic interests, the delay of the work should LOCATION AND CONSTRUCTION OF OPEN DITCHES 213 TABLE XIV Excavation and Embankment Area in Feet 0.00 O.IO 0.20 0.30 0.40 o.so 0.60 0.70 0.80 0.90 0.00 0-37 0-74 I. II 1.48 1.85 2.22 2.59 2.96 3-33 I 3.70 4-07 4-45 4.81 S-19 5-56 5-93 6.30 6.67 7-04 2 7.41 7.78 8.15 8.52 8.89 9.26 9-63 10.00 10.37 10-74 3 II. II 11.48 11.85 12.22 12-59 12.96 13-33 13-70 14.07 14-44 4 14.82 15-19 15-56 15-93 16.30 16.67 17-04 17-41 17.78 18-15 s 18.32 18.89 19.26 19-63 20.00 20.37 20.74 21.11 21.48 21.85 6 22.22 22-59 22.96 23-33 23-70 24.07 24.44 24.82 25-19 25-56 7 25.93 26.30 26.67 27.04 27.41 27.78 28.IS 28.52 28-89 29.26 8 29.63 30.00 30.37 30.74 31-11 31-48 31.85 32.22 32-59 32.96 9 33-33 33.70 34.07 34.44 34-82 35-19 35.56 35.93 36-30 36.67 10 37.04 37.41 37.78 38.15 38-52 38.89 39-26 39-63 40.00 40.37 II 40.74 41.11 41.48 41.85 42.22 42.59 42.96 43-33 43-70 44-07 12 44-44 44-82 45-19 45.56 45-93 46.30 46.67 47-04 47-41 47-78 13 48.15 48-52 48.89 49.26 49-63 50.00 50.37 50-74 51-11 51.48 14 51.85 52-22 52.59 52.96 53-33 53-70 54-07 54-44 54-82 55-19 IS 55.56 55-93 56.30 56.67 S7-04 57-41 57-78 58-15 58.52 58-89 16 59-26 59-63 60.00 60.37 60.74 61.11 61.48 61.85 62.22 62.59 17 62.96 63-33 63-70 64.07 64.44 64.82 65-19 65-56 65-93 66.30 18 66.67 67.04 67-41 67-78 68.15 68.52 68.89 69-26 69-63 70.00 19 70.37 70.74 71-11 71-48 71.85 72.22 72.59 72.96 73-33 73-70 20 74-07 74-44 74-82 75-19 75.56 75-93 76.30 76.67 77.04 77-41 21 77-78 78-15 78-52 78.89 79-26 79-63 80.00 80.37 80.74 81.11 22 81.48 81-85 82.22 82.59 82.96 83-33 83.70 84.07 84.44 84.82 23 85.19 85-56 85-93 86.30 86.67 87-04 87-41 87.78 88.15 88.52 24 88.89 89.26 89-63 90.00 90.37 90.74 91.11 91.48 91-85 92.22 2S 92.59 92.96 93 .33 93-70 94.07 94.44 94.82 95-19 95-56 95-93 26 96.30 96.67 97-04 97-41 97.78 98.15 98.52 98.89 99.26 99-63 27 100.00 100.37 100.74 lOI.Il 101.4S 101.85 102.22 102.59 102.96 103-33 28 103.70 104.07 104.44 104.82 105.19 105.56 105.93 106.30 106.67 107.04 29 107-41 107.78 108.15 108.52 108.89 109.26 109.63 110.00 110.37 110.74 30 III. 11 111.48 III.85 112.22 112.59 112.96 113-33 113.70 114.07 114-44 31 1 14-81 115.18 115.56 115.92 116.29 116.67 117-03 117.40 117.77 118.15 32 118.52 118.89 119.26 119.63 120.00 120.37 120.74 121. II 121.48 121.85 33 122.22 122.59 122.96 123-33 123.70 124.07 124.44 124-81 125.18 125.55 34 125.92 126.30 126.66 127.03 127.40 127.77 128.14 128.51 128.88 129.26 35 129.63 130.00 130-37 130.74 131.11 131-48 131-85 132.22 132.59 132.96 36 133-33 133-70 134-07 134-44 134.81 135-18 135-55 135-92 136.29 136.67 37 137-04 137-41 137-78 138-15 138.52 138-89 139-26 139-63 140.00 140-37 38 140-74 141. II 141.48 141-85 142.22 142-59 142.96 143-33 143-70 144-07 39 144-44 144.81 145-18 145-55 145-92 146.29 146.66 147-03 147.40 147.78 40 148.15 148.52 148.89 149.26 149-63 150.00 150.37 150-74 151-n 151-48 41 151-85 152.22 152-59 152.96 153-33 153-70 154.07 154-44 154-81 155-18 42 155-55 155-92 156-29 156.66 157-03 157-40 157.77 158.14 158-51 158-89 43 159-26 159-63 160.00 160.37 160.74 161. II 161.48 161.85 162.22 162.59 214 ENGINEERING FOR LAND DRAINAGE TABLE XIV— Continued Area in Feet 0.00 O.IO 0.20 0.30 0.40 o.so 0.60 0.70 0.80 0.90 44 162.96 163.33 163.70 164.07 164.44 164.81 165.18 i6S-S5 165.92 166.30 45 166.67 167.04 167.41 167.78 168.J5 168.52 168.89 169.26 169.63 170.00 46 170.37 170.74 171. II 171.48 171.85 172.22 172.59 172.96 173-33 173.70 47 174-07 174.44 174.81 175.18 175-55 175-92 176.29 176.66 177.03 177.41 48 177.78 178.15 178.52 178.89 179.26 17963 180.00 180.37 180.74 181.II 49 181.48 181.8s 182.22 182.59 182.96 183-33 183.70 184.07 184.44 184.81 SO 183.18 185.55 185.92 186.29 186.66 187-03 187.40 187.77 188.14 188.52 SI 188.89 189.26 189.63 190.00 190.37 190-74 191.11 191.48 191.8s 192.22 S2 192.59 192.96 19333 193-70 194-07 194.44 194.81 19518 195.55 195-93 S3 196.30 196.67 197.04 197.41 197-78 198.15 198.52 198.89 199-26 199.63 S4 200.00 200.37 200.74 201. II 201.48 201.85 202.22 202.59 202.96 203-33 55 203.70 204.07 204.44 204.81 20S.18 205.55 205.92 206.29 206.66 207.03 56 207.41 207.78 208.15 208.52 208.89 209.26 209.63 210.00 210.37 210.74 57 211. 11 211.48 211.85 212.22 212.59 212.96 213-33 213.70 214.07 214.44 S8 214.81 2IS.18 215-55 215.92 216.29 216.66 217.03 217.40 217.77 218.15 S9 218.52 218.89 219.26 219.63 220.00 220.37 220.74 221. II 221.48 221.8s 6o 222.22 222.59 222.96 223.33 223.70 224.07 224.44 224.81 225.18 225.55 6i 225.92 226.29 226.66 227.03 227-40 227.77 228.14 228.51 228.88 229.26 62 229.63 230.00 230.37 230.74 231.11 231.48 231-85 232.22 232.59 232.96 63 233-33 233.70 234-07 234.44 234.81 235-18 235.55 235-92 236.29 236.67 64 237-04 237.41 237-78 238.15 238.52 238.89 239.26 23963 240.00 240.37 6s 240.74 24I.II 241.48 241.85 242.22 242.59 242.96 243-33 243-70 244.07 66 244-44 244.81 245.18 24S-5S 24592 246.30 246.67 247-04 247.41 247.78 67 248.15 248.52 248.89 249.26 249-63 250.00 250.37 250-74 251.11 251.48 68 251-85 252.22 252.59 252.96 253-33 253.70 254-07 254-44 254.81 255.18 69 255-56 25593 256.30 256.67 257.04 257.41 257-78 258-lS 258.52 258.89 70 259.26 259-63 260.00 260.37 260.74 261. II 261.4S 261.8s 262.22 262.59 71 262.96 263.33 263.70 264.07 264.44 264.81 265.18 265-55 265.92 266.30 71 266.67 267.04 267.41 267.78 268.15 268.52 268.89 269.26 269.63 270.00 73 270.37 270.74 271. II 271.48 271.85 272.22 272.59 272.96 273-33 273.70 74 274.07 274.44 274.81 275-18 275-55 275.92 276.29 276.66 277-04 277.41 75 277.78 278.15 278.52 278-89 279-26 279-63 280.00 280.37 280-74 281.11 76 281.48 281.85 282.22 282.59 282.96 283.33 283.70 284.07 284.44 284.81 77 285.18 285.56 285.93 286.30 286.67 287.04 287.41 287.78 288.IS 288.52 78 288.89 289.26 289.63 290.00 290.37 290.74 291. II 291.48 291.85 292.22 79 a92.59 292.96 293-33 293-70 294-07 294-44 294.81 295-18 295-55 29593 80 296.30 296.67 297-04 297-41 297.78 298.15 298.52 298.89 299.26 29963 81 300.00 300.37 300.74 3OI-II 301.48 301.8s 302.22 302.59 302.96 30333 82 303.70 304-07 304-44 304.81 305.18 305-55 305-92 306.29 306.66 307.03 83 307-41 307-78 308-15 308.52 308.89 309.26 30963 310.00 310-37 310.74 84 3ii.ll 311-48 311-85 312.22 312.59 312.96 313.33 31370 314-07 314.44 8S 314-81 315-19 315-56 31593 316-30 316.67 31704 1 317.41 317-78 318.1S 86 318-52 318.89 31926 319-63 320.00 320.37 320.74J 321. II 321.48 321.85 87 322.22 322.59 322.96 323-33 323-70 324-07 324.44 324-81 325-18 325.5s 88 32S-9> 326.30 326.67 327-04 327-41 327.78, 328.15! 328.52 328.89 329.26 89 3*9-63 330-oo| 330.37 330-74 3311 1 33I.48| 331-85! 332-221 332.S9 332-96 LOCATION AND CONSTRUCTION OF OPEN DITCHES 215 TABLE Xrv— Continued Area in Ft. 0.00 O.IO 0.20 0.30 0.40 0.50 0.60 0.70 0.80 G.yO 90 333-33 333.70 334-07 334-44 334.81 335-18 335-55 335.92 336.29 336-67 91 337.04 337-41 337.78 338-15 338.52 338-89 339-25 339.62 339.99 340.37 92 340.74 34I.II 341.48 341-85 342.22 342-59 342-96 343.33 343.70 344-07 93 344.44 344-81 34S-I8 345-56 345-93 346.30 346-67 347.03 347.40 347-78 94 348.15 348-52 348.89 349-26 34963 350.00 350.37 350.74 351-11 351-48 95 351.85 352-22 352-59 352.96 353-33 353-70 354-07 354-44 354-81 355.18 96 355.5s 355-93 356-30 356.67 357-04 357-41 357.78 358-15 358.52 358-89 97 35926 359-63 360.00 360.37 360.74 361.11 361.48 361.85 362.22 362-59 98 362.96 363-33 363-70 364-07 364.44 364.81 365-18 365-55 365-93 366.30 99 366.67 367-04 367-41 367.78 368.IS 368.52 368.89 369-26 369-63 370.00 100 370.37 370-74 371-11 371-48 371.85 372.22 372-59 372-96 373-33 373.70 10 1 374.07 374-44 374.81 375-18 375-55 375-92 376.29 376-67 377-04 377.41 102 377-78 378-15 378-52 378.89 379-26 379-63 380.00 380.37 380.74 38I-II 103 381.48 381-85 382-22 382.59 382-96 383-33 383-70 384-07 384-44 384-81 104 385.18 385-55 385-92 386.29 386-67 387.04 387-41 -387-78 388.15 388.52 105 388.89 389.26 389.63 390.00 390-37 390.74 391. II 391-48 391-85 392-22 106 392.59 392.96 393.33 393.70 394-07 394-44 394-81 395-18 395-55 395-92 107 396.30 396-67 397.04 397.41 397-78 398.15 398-52 398-89 399.26 399-63 108 400.00 400.37 400.74 401.11 401.48 401-85 402.22 402-59 402-96 403-33 109 403.70 404.07 404.44 404.81 40518 405-55 405-92 406-29 406.67 407-04 no 407.41 407.78 408.15 408.52 408.89 409-26 409-63 410.00 410-37 410.74 III 411. IX 411.48 411.85 412.22 412.59 412.96 413-33 413.70 414-07 414-44 112 414.81 415.18 415.55 415.92 416.29 416-67 417-04 417.41 417-78 418-15 113 418.52 418-89 419.26 419.63 420.00 420.37 420.74 421.11 421 -48 421-85 114 422-22 422-59 422.96 42333 423.70 424.07 424-44 424.81 425-18 425-56 "5 425-93 426.30 426.67 427.04 427.41 427.78 428.15 428.52 428.89 429-26 116 429-63 430.00 430.37 430.74 431. II 431-48 431-85 432.22 432.59 432-96 117 433.33 433-70 434.07 434-44 434-81 435-18 435-55 435-92 436.29 436-67 118 437.04 437-41 437.78 438.15 438-52 438-89 439-26 439-63 440.00 440-37 119 440.74 44I-II 441.48 441.85 442-22 442-59 442-96 443-33 443-70 444-07 120 444.44 444.81 445.18 445.55 445-92 446-29 446-67 447.04 447-41 447-78 121 448.15 448.52 448-89 449.26 449-63 450.00 450-37 450-74 451. II 451-48 122 451.85 452.22 452-59 452.96 453-33 453-70 454-07 454-44 454-81 455-i8 123 455-55 455-92 456-29 456.67 457-04 457-41 457-78 458-15 458-52 458-89 124 459-26 459-63 460.00 460.37 460.74 461.11 461.48 461.8s 462-22 462-59 125 462-96 463-33 463-70 464.07 464-44 464.81 465-18 465-55 465-93 466-30 126 466-67 467.04 467-41 467.78 468.15 468.52 468.89 469.26 469-63 470.00 127 470-37 470-74 471-11 471-48 471-85 472.22 472.59 472.96 473-33 473-70 128 474-07 474-44 474-81 475-18 475-56 475.93 476.30 476.67 477-04 477-41 129 477-78 478-15 478-52 478-89 479-26 479.63 480.00 480.37 480.74 481-11 130 481.48 481.85 482-22 482-59 482-96 483.33 483-70 484.07 484-44 484-Si 131 485-18 485-55 485-92 486.29 486-67 487.04 487-41 487-78 488.15 488-52 132 488.89 489.26 489-63 490.00 490-37 490.74 491.11 491-48 491-85 492-22 133 492-59 492.96 493-33 493-70 494-07 494.44 494.81 495-19 495-56 495-93 134 496-30 496-67 497-04 497-41 497-78 498.15 498.52 498-89 499.26 499-63 I3S 500.00 500.37 500-74 501.11 501-48 S01.85 502.22 502-59 502-96 503-33 ,2X6 ENGINEERING FOR LAND DRAINAGE TABLE XIV— Continued Area in Ft. 0.00 O.IO 0.20 0.30 0.40 o.so 0.60 0.70 0.80 0.90 136 503-70 504-07 504.44 504-81 505.18 S05-56 505.93 506.30 506.67 507.04 isr 507.41 507.78 508.IS 508-52 508.89 509-26 SO9.63 510.OC S10.37 SI0.74 138 511. II 511-48 511.85 512-22 S12.59 512-96 51333 513.70 S14-07 514.44 139 514.81 S15-18 515.SS 515-92 516.29 516-67 517.04 S17-41 517-78 5I8.IS 140 518.52 518.89 519-26 519-63 520.00 520.37 520.74 521.11 521.48 521.8s 141 522.22 522.59 522.96 523-33 S23.70 524.07 524.44 524.81 525.19 535-56 142 52593 526.30 526.67 527-04 527.41 527.78 528.IS 528.52 528.89 529-26 143 529.63 530.00 530.37 530-74 53I-II 531-48 531-85 532.22 532-59 532-94 144 533.33 533-70 534.07 534-44 534-81 535-18 535-56 535.93 536-30 536-67 I4S 537.04 537.41 537-78 538-15 538-52 538-89 539-26 53963 S4O.0O 540-37 146 540.74 541. II 541.48 541.85 542-22 542-59 542-96 543-33 543-70 544-07 147 544.44 544.81 545.18 545.56 545-93 546-30 546.67 547-04 547-41 547-78 148 548.15 548.52 548.89 549-26 549-63 550.00 550.37 550.74 551-11 551-48 149 551.85 552.22 552.59 552-96 553-33 553.70 554-07 554.44 554-81 SSS-18 ISO 555-55 555.93 556.30 556.67 557-04 557-41 557-78 558.15 558-52 558-89 ISI 559.26 559-63 560.00 560.37 560-74 561.11 561.48 561.8s 562.22 562.59 IS2 562.96 563-33 563.70 564-07 564-44 564.81 565.18 565-56 565-93 566.30 153 566.67 567-04 567.41 567.78 S68.15 568.52 S68.89 569-26 569-63 S70.0O 154 570.37 570-74 571.11 571-48 571.85 572.22 572.59 572-96 573-33 573-70 ISS 574.07 574-44 574.81 575-18 575-56 575-93 576.30 576.67 577-04 577.41 IS6 577-78 578.15 578.52 578-89 579-26 579-63 580.00 580.37 580-74 581.11 157 581.48 581.8s 582.22 582.59 582-96 583-33 583-70 584.07 584-44 584.81 IS8 585.18 585.55 585-92 586.29 586-66 587.04 587.41 587.78 588-lS 588.52 1S9 588.89 589.26 589-63 590.00 590-37 590.74 591-11 591-48 591-85 592.22 1 6a 592.59 592-96 593-33 593-70 594-07 594-44 594-81 595-18 595-55 595-92 161 596.29 596-67 597-04 597-41 597-78 598-15 598.52 598-89 599-26 599-63 162 600.00 600.37 600-74 601-11 601.48 601.85 602-22 602-59 602.96 603-33 163 603.70 604.07 604-44 604.81 605.18 605.55 605.92 606-30 606.67 607-04 164 607.41 607.78 60S. 1 5 608.52 608.89 609.26 609.63 610.00 610.37 610-74 I6S 6ii.ii 611.48 611.85 612.22 612.59 612.96 613.33 613.70 614.07 614-44 166 614.81 615.18 615.55 615.92 616.29 616.67 617.04 617-41 617.78 618.15 167 61S.52 618.89 619.26 619.63 6ao.oo 620.37 620.74 621-II 621.48 621-85 168 622.22 622.59 622.96 623.33 623.70 624.07 624.44 624.81 625.18 625.56 169 625-93 626.30 626.67 627.04 627.41 627.78 628.15 628.52 628.89 629.26 170 629-63 630.00 630.37 630.74 631. II 631.48 631.85 632.22 632.59 632.96 171 63333 633-70 634.07 634.44 634.81 635.18 635-55 63592 636.29 636.66 172 637.04 637.40 637.77 638.14 638.51 638.88 63925 639.62 639.99 640.37 173 640.74 641. II 641.48 641.85 642.22 642.59 642-96 643-33 64370 644-07 174 644.44 644.81 645.18 645-55 645-92 646.29 646-66 647-03 647-41 647-78 175 648.15 648.5a 648.89 649.26 649.63 650.00 650-37 650-74 651.11 651.48 176 651.85 653.22 652.59 652.96 653.33 653.70 654.07 654-44 654-81 6SS.18 177 655-56 655.93 656.30 656.67 657.04 657.41 657-78 658- IS 658.52 658.89 178 6s9.a6 659-63 660.00 660.37 660.74 661-II 661.48 661-85 662.32 663.59 179 662.96 663-33 663.70 664.07 664.44 664.81 665.18 665-55 665.92 666.29 180 666.67 667-04 667.41 667.78 668. IS 668.52 668.89 669.26 669.63 670.00 181 670-37 670.74 671. II 671.481 671.85I 672.22 672.59 672.96 673.33 673-70 LOCATION AND CONSTRUCTION OF OPEN DITCHES 217 TABLE XIV— Continued Area in Ft. 0.00 O.IO 0.20 0.30 675-18 0.40 0.50 0.60 0.70 o.go 0.90 182 674-07 674.44 674-81 673-55 675-93 676.30 676.67 677-04 677-41 183 677.78 678.15 678.52 678.89 679.26 679-63 680.00 680.37 680.74 681. 11 184 681.48 681.8s 682.22 682.39 682.96 683-33 684.70 684.07 684.44 684.81 185 685.18 685.56 685.93 686.30 686.67 687.04 687.41 687.78 688.15 688.52 186 688.89 689.26 689.63 690.00 690.37 690.74 691.11 691.48 691.85 692.22 187 692.59 692.96 693.33 693.70 694.07 694.44 694.81 695.18 695.35 695.92 188 696.30 696.67 697.04 697.41 697.78 698.15 698.52 698.89 699.26 699.63 189 700.00 700.37 700.74 701. II 701.48 701.83 702.22 702-59 702.96 703.33 igo 703.70 704-07 704.44 704.81 705-18 705-55 705.92 706.29 706.66 707.03 191 707.40 707-77 708.14 708.51 708.89 709.26 709.63 710.00 710.37 710.74 192 711. II 711-48 711.85 712.22 712.59 712.96 713.33 713.70 714-07 714-44 193 714.81 7IS-I8 715.55 715.92 716.29 716.67 717.04 717-41 717.78 718.15 194 718.52 718.89 719.26 719-63 720.00 720.37 720.74 721. II 721.48 721.85 19s 722.22 722.59 722.96 723-33 723.70 724.07 724-44 724-81 725-18 725-55 196 725.92 726.29 726.66 727-03 727.40 727.77 728.14 728.51 728.88 729-25 197 729.63 730.00 730.37 730-74 73I-II 731.48 731-83 732-22 732.39 732-96 198 733.33 733.70 734.07 734-44 734.81 735.18 733.53 733-93 736-30 736.67 199 737-04 737-41 737-78 738.15 738.52 738.89 739-26 739-63 740.00 740.37 200 740.74 74I-II 741-48 741-85 742.22 742.59 742-96 743-33 743.70 744.07 201 744.44 744-81 745-18 743-53 745-93 746.30 746.67 747.04 747.41 747.78 202 748.1S 748-52 748-89 749-26 749-63 750.00 730.37 730.74 751-11 751-48 203 751.85 752.22 732-59 752.96 753-33 733.70 734-07 754.44 734-81 735-18 204 755-55 755-93 756.30 736.67 757-04 757-41 757.78 758.15 758-52 758-89 20s 759-26 759-63 760.00 760.37 760.74 761.11 761.48 761-85 762.22 762.39 206 762.96 763-33 763.70 764.07 764.44 764.81 763.18 765-55 765.93 766.30 207 766.66 767-04 767.41 767.78 768.13 768.52 768.89 769.26 769-63 770.00 208 770.37 770-74 771-11 771.48 771.83 772.22 772.39 772.96 773-33 773-70 209 774-07 774-44 774-81 773.18 775.55 775.93 776.30 776.66 777-04 777-41 210 777-78 778.15 778-52 778.89 77926 779-63 780.00 780.37 780.74 781.11 211 781.48 781.85 782.22 782.39 782.96 783.33 783.70 784-07 784.44 784.81 212 785.18 783.53 785.93 786.30 786.66 787.04 787.41 787-78 788.15 788.52 213 788.89 789.26 789.63 790.00 790-37 790.74 791-11 791-48 791-85 792.22 214 792.59 792.96 793.33 793.70 794-07 794.44 794-81 793-18 795.55 7»3.93 215 796.30 796.66 797.04 797-41 797-78 798.15 798-52 798-89 799-26 799-63 216 800.00 800.37 800.74 801. II 801.48 801.83 802.22 S02.39 802.96 803-33 217 803.70 804.07 804.44 804.81 803.18 805.55 803.93 806.30 806.66 807-04 218 807.41 807.78 808.15 808.32 808.89 809.26 809.63 810.00 810.37 810.74 219 811. II 811.48 811.85 812.22 812.59 812.96 813-33 813.70 814.07 814.44 220 814.81 815.18 815-55 815-93 816.30 816.66 817-04 817.41 817.78 818.15 221 818.52 818.89 819.26 819.63 820.00 820.37 820.74 821.11 821.48 821.8s 222 822.22 822.59 822.96 823.33 823.70 824.07 824.44 824.81 825.18 823.33 223 825-93 826.30 826.66 827.04 827.41 827.78 828.13 828.52 828.89 829.26 224 829.63 830.00 830.37 830.74 831.11 831.48 831-85 832.22 832-59 832.96 22s 833.33 833-70 834-07 834-44 834.81 833-18 835-55 833-93 836.30 836.66 226 837.04 837-41 837-78 838-13 838.52 838.89 839.26 839-63 840.00 840.37 227 840.74 841. 1 1 841-48 841.83 842.22 842.39 842.96 843-33 843-70 844-07 2l8 ENGINEERING FOR LAND DRAINAGE TABLE XIV— Continued Area in Ft. 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 847.04 0.80 o.go 228 844.44 844.81 845.18 845-55 845-93 846.30 846.66 847.41 847.78 229 848.15 848.52 848.89 849.26 849-63 850.00 850.37 850.74 851. II 851.48 230 851.85 852.22 852.59 852.96 853-33 853-70 854-07 854-44 8s4-8i 855-18 231 855.55 855-93 856.30 856.66 857.04 857-41 857.78 858.15 858-52 858.89 232 859.26 859-63 860.00 860.37 860.74 861-11 861-48 861.85 862-22 862.59 233 862.96 863.33 863.70 864.07 864.44 864.81 865-18 865-55 865.93 866.30 234 866.66 867.04 867.41 867.78 868.15 868.52 868.89 869.26 869.63 870.OU 235 870.37 870.74 871.11 871.48 871.85 872.22 872.59 872.96 873.33 873-70 236 874.07 874.44 874.81 875.18 875-55 875.93 876.30 876.66 877.04 877-41 237 877.78 878.15 878.52 878.89 879.26 879-63 880.00 880.37 880.74 881.11 238 881.48 881.85 882.22 882.59 882.96 883-33 883.70 884.07 884.44 884.81 239 885.18 885.55 885.93 886.30 886.66 887.04 887.41 887.78 888.IS 888.52 240 888.88 889.26 889.63 Sgo.oo 890.37 890.74 891. II 891.48 891.85 892.22 241 892.59 892.96 893.33 893.70 894-07 894.44 894.81 895.18 895-55 895-93 242 896.30 896.66 897.04 897.41 897.78 898.15 898.52 898.88 899.26 899-63 243 900.00 900.37 900.74 901. II 901.48 901.85 902.22 902.59 902.96 903.33 244 903.70 904.07 904.44 904.81 905.18 905-55 905-93 906.30 906.66 907.04 24S 907.41 907.78 908.15 908.52 go8.88 909-26 909-63 910.00, 91D.37 910.74 246 911. II 911-48 911.85 912.22 912.59 912.96 913-33 913-70 914-07 914.44 247 914.81 915-18 915-55 915.93 916.30 916.66 917-04 917-41 917-78 918.IS 24S 918.52 918.88 919-26 919-63 920.00 920.37 920.74 921. II 921.48 921.85 249 922.22 922.59 922.96 923.33 923.70 924.07 924.44 924-81 925.18 925-55 250 92592 926.30 926.66 927-04 927.41 927.78 928.IS 928.52 928.88 929-26 251 929.63 930.00 930.37 930-74 931.11 931.48 931.85 932.22 932.59 932.96 2S2 933.33 933-70 934-07 934-44 934.81 935-18 935.55 935-92 936.30 936.66 253 937-04 937.41 937-78 938.15 938.52 938-88 939.26 939-63 940.00 940.37 254 940.74 941-11 941-48 941.85 942.22 942.59 942.96 943-33 943.70 944-07 2SS 944-44 944-81 945.18 945-55 945-92 946.30 946-66 947.04 947-41 947-78 256 948.15 948.52 948.88 949-26 949-63 950.00 950-37 950-74 951. II 951-48 257 951-85 952.22 952.59 952-96 953-33 953.70 954-07 954.44 954-81 95518 258 955-55 95S-92 956.30 956-66 957-04 957.41 957-78 958.15 958-52 958.88 259 959-26 959-63 960.00 960.37 960.74 961. IX 961.48 961.85 962.22 962.59 260 962-96 963.33 963.70 964.07 964.44 964.81 965.18 965-55 965-92 966.30 261 966.66 967-04 967.41 967.78 968.15 968.52 968.88 969.26 969-63 970.00 262 970.37 970.74 971-11 971.48 97f.85 972.22 972.59 972.96 973.33 973-70 263 974.07 974-44 974-81 975.18 975.55 975-92 976.30 976.66 977-04 977.41 264 977.78 978-15 978-52 978.88 979-26 97963 980.00 980.37 980.74 981.II 265 981.48 981.85 982.22 982.59 982.96 983.33 983.70 984.07 984.44 984.8X 266 985.18 985-55 985.92 986.30 986.66 987.04 987-41 987.78 988.1s 988-5i 267 988.88 9S9.26 989-63 990.00 990.37 990.74 991 -11 991-48 991.85 992-22 268 992-59 992.96 993.33 993-70 994.07 994-44 994.81 995-18 995.55 995-92 269 996-30 996.66 997.04 997-41 997.781 998.15 998.52 998-88 999.26 999-63 270 1000.00 1000.37 1 000.74 1 001. II 1001.48 1001.8$ 1002.32 1002.59 1002.96 1003.33 271 1003.70 1004.07 1004.44 1004.81 1005.18 1005.55 :005.9a 1006.3a 1006.66 1007.04 272 1007.41 1007.78 1008.1S 1008.5a 1008.88 1009.26 1009.63 1010.00 [010.37 1010.74 273 lOII.II loi 1.48 1011.85^1012. 22! ■ 012.59 1012.96 1013.33 1013.70 10x4.07 1014.44 LOCATION AND CONSTRUCTION OF OPEN DITCHES 219 TABLE XIV— Continued 1014.S1 1018.52 1022.22 1025.92 1029.63 1033.33 1037.04 1040.74 1044.44 1048.1S 1051.8s 1055-55 1059.26 1062.96 1066.66 1070.37 1074.07 1077.78 1081.48 1085.18 1088.88 1092.59 1096.30 1100.00 1103.70 1 107.41 nil. II 1 1 14.82 1118.52 1122.22 1125.93 1129.63 1133.33 1137.04 1140.74 1144.44 1148-15 1151-85 1155-56 1159.26 1162.96 1166.67 1170.37 1174.07 1177.78 1181.48 1015.18 IO18.8S 1022.59 1026.30 1030.00 1033-70 1037-41 I04I.II 1044.81 1048.52 1052.22 1055.92 1059.63 1063.33 1067.04 1070.74 1074.44 IO78.IS 1081.85 1085.55 1089.26 1092.96 1096.66 1100.37 1104.07 1107.78 1111.48 1115.19 1118.89 1122.59 1126.30 1130.00 1133.70 1137.41 1141. II 1144.82 1148.52 1152.22 1155-93 1159-63 1163-33 1167.04 1170.74 1174.44 II78.IS 1181.8s IOI5.SS 1019.26 1022.96 1026.66 1030.37 1034.07 1037.78 1041.48 1045.18 1048.88 1052.59 1056.30 1060.00 1063.70 1067.41 IO71.II 1074.81 1078.52 1081.22 1085.92 1089.63 1093.33 1097.04 1100.74 1104.44 1108.15 1111.85 1115.56 1119.26 1122.96 1126.67 1130-37 1134.07 1137.78 1141.48 1145.19 1148.89 1152.59 1156.30 ti6o.oo 1163.70 1167.41 1171.11 1 174.82 1178.52 1182.22 0.30 0.40 o.so 0.60 0.70 1015.92 1019.63 1023.33 1027.04 1030.74 1034-44 1038.15 1041.85 1045-55 1049.26 1052.96 1056.66 1060.37 1064.07 1067.78 1071.48 1075.18 1078.88 1082.59 1086.3a 1090.00 1093.70 1097.41 IIOI.II 1104.81 1108.52 1112.22 1115.93 1119.63 1123-33 1127.04 1130.74 1134.44 1138.15 1141.85 1145-56 1149.26 1152.96 1156.67 1160.37 1164.07 1167.78 1171.48 1175-19 1178.89 1182.59 1016.30 1020.00 1023.70 1027.41 1031.11 1034.81 1 1038.52 1042.22 1045.92 1049.63 1053-33 ,1057-04 1060.74 1064.44 1068.15 1071.85 1075-55 1079.26 1082.96 '1086.66 ,1090.37 1094.07 1097.78 1101.48 1105.18 1108.88 1112.59 1116.30 1120.00 1123.70 1127.41 1131.I1 1134.82 1138.52 1142.22 1145.93 1149-63 1153-33 1157-04 1160.74 1164.44 1168.15 1171-85 1175-56 1179.26 1182.96 1016.66 1017.04 1020.37 1020.74 1024.07.1024.44 1027.78 1028.15 1031.48 1031.85 1035.18,1035.55 1038.8S' 1039.26 1042.59 1042.96 1046.30.1046.66 1050.00 1050.37 1053-70,1054.07 1057.41 1057.78 1061.11 1061.48 1064.81 1065.18 1068.52 1068.88 1072.22 1072.59 1075.92 1076.30 1079.63 1080.00 1083.33 1083.70 1087.04 1087.41 1090.74 1091. II 1094.44' 1094.81 1098.15 ID98.52 1101.85 1105.55 1109.26 1112.96 1116.67 1120.37 1124.07 1127.78 I131.48 1135-19 1138.89 1142.59 1146.30 1150.00 1153.70 1157.41 ii6i.ii 1164.82 1168.52 1172.22 1175-93 1179.63 1183.33 1102.22 1105.92 1109.63 1113.33 1117.04 1120.74 1124.44 1128.15 1131.85 1135.56 1139.26 1142.96 1146.67 1150.37 1154-07 1157-78 1161.48 1165.19 1168.89 1172.59 1176.30 1180.00 1183.70 1017.41 1021.11 1024.81 1028.52 1032.32 1035.92 1039.63 1043.33 1047.04 1050.74 1054.44 1058.15 1061.85 1065.55 1069.26 1072.96 1076.66 1080.37 1084.07 1087.78 1091.48 1095.18 1098.88 1102.59 1106.30 1110.00 1113.70 1117.41 1121.11 1124.82 1128.52 1132.22 1135-93 1139-63 1143-33 1147.04 1150.74 1154.44 1158-15 1161.85 1165.56 1169.26 1172.96 1176.67 1180.37 1184.07 1017.78 1021.48 1025.18 1028.88 1032.59 1036.30 1040.00 1043.70 1047.41 1051.11 1054.81 1058.52 1062.22 1065.92 1069.63 1073-33 1077.04 1080.74 1084.44 108S.15 IO18.15 1021.85 1025.55 1029.26 1032.96 1036.66 1040.37 1044.07 1047.78 1051.48 1055.18 1058.88 1062.59 1066.30 1070.00 1073.70 1077.41 1081.11 1084.81 1088.52 1091.85 1092.22 1095.55 '1995.92 1099.26 1099.63 1102.96 1103.33 1106.66 1107.04 1110.37,1110.74 1114.07,1114.44 1117.78 I118.1S 1121.48 1121.85 1125.19 1125.56 1128.89 1129.26 1132.59I1132.96 1136.30^1137.67 1140.00 1140.37 1143-70 1144-07 1147-41 I151.11 1154.82 158.52 1162.22 1165.93 1169.63 173.33 : 1 77-04 :l8o.74 1147.78 1151-48 1155-19 1158.89 1162.59 1166.30 1170,00 1173.70 1177.41 iiSi.ii 1184.44 1184.82 220 ENGINEERING FOR LAND DRAINAGE TABLE XIV— Continued 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1185.19 1188.89 1192.59 1196.30 1200.00 1203.70 1207.41 x211.11 1214.82 1218.52 1222.22 1225.93 1229.63 1233.33 1237.04 1240.74 1244.44 1248.15 1251.85 1255.56 1259.26 1262.96 1266.67 1270.37 1274.07 1277.78 1281.48 1285.19 1288.89 1292.59 1296.30 X300.00 1303.70 1307.41 1311.11 1314.82 1318.52 1322.22 1325.93 1329.63 |ii85-S6 1189.26 1192.96 1196.67 1200.37 1204.07 1207.78 1211.48 1215.19 1218.89 1222.59 1226.30 1230.00 1233.70 1237.41 1241.11 1244.82 1248.52 1252.22 ■255.93 1259.63 1263.33 1267.04 1270.74 1274-44 1278.15 1281.85 1285.56 1289.26 1292.96 1296.67 1300.37 1304.07 1307.78 1311.48 1315-19 1318.89 1322.59 1326.30 1330.00 1185-93 1189.63 1193-33 1197-04 1200.74 1204.44 1208.15 1211.85 1215.56 1219.26 1222.96 1226.67 1230.37 1234.07 1237.78 1241.4S 1245.19 1248.89 1252.59 1256.30 1260.00 1263.70 1267.41 1271.11 1274.82 1278.52 1282.22 1285.93 1289.63 1293.33 1297.04 1300.74 1304.44 1308.15 1311.85 1315-56 1319.36 1333.96 1326.67 1330.37 1186 1190, 1193 1197, 1201 1204. 1208. 1212. 1215, l2lg. 1223 1227. 1230. 1234. 1238. 1241 1245. 1249, 1252, 1256, 1260. 1264. 1267, 1271. 1275- 1278. 1282, 1286. 1290, IW3. 1297. 1301. 1304. 1308. 1312. 1315. 1319- 1323. 1327- 1330- 30 1186-67 00 1190-37 -70 1194-07 41 1197-78 1201.48 1205.19 1208.89 1212.59 1216.30 1220.00 1223.70 1227.41 I23I.1I 1234.82 1238.52 .85:1242.22 1.56 .26 .96 ■67 •37 .07 .78 .48 ,19 ,89 59 ,30 ,00 70 41 II •82 ■53 23 93 63 33 04 74 1245-93 1249.63 1253.33 1257.04 1260.74 1264.44 1268.15 1271.85 1275.56 1279.26 1282.96 1286.67 1290.37 1294.07 1297.78 1301.48 1305-19 1308.89 J312.59 1316.30 1320.00 1323-70 1337.41 1331-11 1187.04 1190.74 1194.44 1198.15 1201.85 1205.56 1209.26 1212.96 1216.67 J 220.37 1224.07 1227.78 1231.48 1235.19 1238.89 1242.59 1246.30 1250.00 1253.70 1257-41 1261. II 1264.82 1268.52 1272.22 1275.93 1279.63 1283.33 1287.04 1290.74 1294.44 1298.15 1301.85 1305.56 1309.36 1313.96 1316.67 1320.37 1334.07 1327.78 1331.48 1187. 1191 1 194. 1198. 1202 1205. 1209 1213, 1217 1220. 1224. 1228. 1231 1235 1239 1242. 1246, 1250. 1254. 1257, 1261. 1265. 1268, 1272 1276., 1280. 1283 1287., 1291 1294. 1298. 1302 1305 1309 1313 1317.' 1320. 1334. 1338, 1331 L .41 1 1 187.78 .11 1191.48 ,19 1.89 1.22 '1202.59 .93 1206.30 >.63 1210.00 .33,1213.70 (.82 1195.1 52 I19S.! V III .04 1217.. 1 188 1191 119s 1199. 1202 1206 1210 1214 .74 1221 .44 1224 .15 1228 .85 1 1232 -56|i235 .26 1239 .961243. .671247 1225 1228 ^1 ■37,1250 ■071254 ■73|l258 .48 1261 ■ 19I1265. .89 j 1269. ■41 1217 .11 1221 .81 .52 .22 1232 .93 1 1236 1240 1243 1 1247. '125I. ,1254 1258, 1262. 1265, 1269 ■63 ■33 .04 ■74 ■44 ■15 ■85 56 .26 .96'l273 ■59 1272 .30 1276.67 1 1 377. .00 1280. 7o|l384. .411287. ,11 I39I.48'l39I. J.37,1380 (.07 1384 r.781388. 1295. 1298. 1302. 1306. 1310 1313. 13 1 7. 1331 1334.: 1338 1333 19 1395 .89 1299 ■59 '303. ■30 1306. .00 1310. ■70|i3i4- ■41.1317- II 1331 ■81 1335. ■S3 1338. .33,1333 I5|ii88.52 .85 1192.22 561195.93 .26^1199.63 96^1203.33 1.67 1207.04 .37 1201.74 07,1214.44 781218.15 48| 1221.86 -18 1225-55 .89 1229-26 •59|l232.96 -30 1236-67 .00 1240.37 .70' 1244-07 .41 1247.78 ■ II 1251.48 ■82|i255.l9 .52'l258.89 .22|l262.59 ■93 1266.30 ■63,1270.00 .33 1273-70 ■04JI277-4I 741281. II .44 1284.83 I5'l288.52 .85 1292.22 56|I295.93 26 1299.63 961303-33 67 1307.04 37 1310.74 07 1314-44 78 1318.15 48|i32i.86 18,1325-55 89 1329.26 59,1332-96 LOCATION AND CONSTRUCTION OF OPEN DITC:^IES 221 be only such as is unavoidable. When the necessary preparation has been made, the track must be crossed as quickly as possible by some method that will insure safety to all concerned. Right of way must be secured from the landowners for each public or district ditch. This should give the proper authorities the right to enter upon such land to construct and maintain the ditch, but does not prevent the owners from using the land which is not occupied by the ditch. The width of the strip of land required for the purpose varies with the size of the ditch, but for a minimum dredge ditch should be 80 feet, 120 feet being commonly used for ditches not wider than 40 feet. This strip of land must be secured before the excavation begins, the cost becoming a charge against the districts in the form of damages. Such charges are usually com- puted at a price per acre unless the course of the ditch follows a natural watercourse, in which case the right of way is secured without cost. Table XV shows at a glance the number of acres contained in right-of-way strips of different widths, and will be found conven- ient in making estimates of that kind. Where the ditch is to be made through a wooded dis- trict, the timber on the entire right of way should be cut down and removed, the brush and slashings being burned upon the ground. Stumps twelve or more inches in diameter that are found in the path of the ditch are shattered by dynamite in such a manner that they can be lifted in sections by the dipper of the dredge. To do this effectively the stick of dynamite should be exploded at the base of the stump underneath the sur- face of the ground, better results being obtained if water covers the surface. The smaller stumps can be re- moved by the dipper after the earth about the roots has been partially excavated. 222 ENGINEERING FOR LAND DRAINAGE TABLE XV Acres Required for Right of Way for Ditches of Different Widths Width Acres Acres Width Acres Acres Ft. per 100 Ft. per Mile Ft, per 100 Ft. per Mile I .002 .121 41 •094 4-97 2 .005 .242 X •094 5- 3 .007 •364 42 .096 5-09 4 .009 .485 43 .099 S.21 5 .oil .606 44 .101 5-33 6 .014 •727 45 .103 5-45 7 .016 .848 46 .106 5-58 8 .018 .970 47 .108 5-70 % .019 I. 48 .110 5.82 9 .021 1.09 49 ^ .112 5-94 10 .023 I.2I 'A .114 6. II .025 1-33 50 •115 6.06 12 .028 1.46 SI .117 6.18 13 .030 1.58 52 .119 6.30 14 .032 1.70 53 .122 6.42 15 •034 1.82 54 .124 6.SS i6 •037 1.94 55 .126 6.67 K .038 2. 56 .129 6.79 17 •039 2.06 57 •131 6.91 i8 .041 2.18 Y •133 7- 19 0.44 2.30 58 •133 703 20 .046 2.42 59 •135 7-15 21 .048 2.5s 60 .138 7.27 22 .051 2.67 61 .140 7-39 23 •053 2.79 62 .142 7-52 24 •055 2.91 63 .145 7.64 Y', •057 3- 64 .147 7.76 25 .057 3-03 65 .149 7.88 26 .060 3-iS 66 .151 8. 27 .062 3-27 67 .154 8.12 28 .064 3-39 68 .156 8.24 29 .067 3-52 69 .158 8.36 30 .069 364 70 .161 8.48 31 .071 3.76 71 .163 8.61 32 •073 3.88 72 .165 8.73 33 .076 4- 73 .168 8.8s 34 .078 4.12 74 .170 8.97 35 .080 4.24 ■4' .170 9- 36 .083 4-36 75 .172 9.09 37 .085 4.48 76 .174 9.21 38 .087 4.61 77 .177 9-33 39 .090 4-73 78 .179 9-45 40 .092 4-85 79 .181 9.58 LOCATION AND CONSTRUCTION OF OPEN DITCHES 223 TABLE XV— Continued Width A cres Acres Width Acres Acres Ft. per 100 Ft. per Mile Ft. per 100 Ft. per Mile 80 184 9.70 H .209 II. 81 186 9.82 91 .209 II.O 82 188 9.94 92 .211 II.2 K 189 10. 93 .213 "•3 83 190 lO.I 94 .216 II.4 84 193 10.2 95 .218 "•5 85 19s 10.3 96 .220 11.6 86 197 10.4 97 .223 11.8 87 200 10.5 98 .225 11.9 88 202 10.7 99 .227 12. 89 204 10.8 100 .230 12.1 90 207 10.9 Bridges. Another point that should not be overlooked in the prosecution of this work is the location of new bridges for farm use. These are not a part of the ditch construction, but should be located in advance in order that the waste banks can be so deposited as to leave a passageway to the bridge when it is constructed. Farm bridges are usually of the wooden truss pattern, but the present tendency is toward steel structures set upon concrete abutments, on account of the heavy machinery and traction engines which both farm and highway bridges are required to support. In order to safely do this they should be designed for a moving load of lOO pounds per square foot, with a factor of safety of 4. Water Inlets. Openings should be required in the banks where tributary streams or ditches enter, but no overfall of water should be permitted at such entrances, the connections being made as suggested in Chap. XV. Water inlets should be located in advance of the con- struction of the ditch, and where practicable should be in the form of large pipes so located and laid that they will discharge near the bottom of the ditch. They 224 ENGINEERING FOR LAND DRAINAGE should be placed in position so that the waste bank can be continuous and the labor of digging through it after the ditch has been completed be avoided. Where the ditch crosses a natural watercourse, as is done in straightening a crooked stream, the natural channel should be closed on the lower side only. It is then used to receive drainage from the lands tributary to it, and discharges into the new channel. In case, however, the old channel is small the banks may be made solid on both sides and water be admitted through them by suitable pipes and sluices. Roadway on Bank. It is frequently desirable to make a highway, public or otherwise, on one of the banks. This, in fact, is a valuable feature of the reclama- tion of large marshes. If the excavated material is wet, it can be spread quite evenly by the operator of the dredge, if care is taken. This, however, slightly in- creases the expense, and if such work is to be required it should be named in the specifications. Stakes should also be set by which the top of the road is to be graded. The guides should be posts well set in the ground at intervals of 300 feet, and cut oil at the height required for the road. They can then be used at any time during the excavation as a guide in distributing the waste banks and, later, in surfacing the road. If sandy mate- rial is found in some parts of the ditch, as is sometimes the case, it can be utilized by depositing it as a top layer on the road. But little shrinkage takes place in such a bank, 3% being the limit if the earth is wet when deposited, and if logs, brush and other foreign material are excluded. Construction. The duties of the engineer in connec- tion with construction consist in setting such stakes as the contractor may need for his guidance in excavating the ditch, inspecting the work to ascertain if the speci- LOCATION AND CONSTRUCTION OF OPEN DITCHES 225 fications are being followed, and making estimates of completed work as required by the terms of the contract. Some permanent grade-stakes should be set in advance of the workmen along the berm at regular intervals, upon which is marked the depth of the channel opposite the points. By the use of cross-bars set above the hubs for sighting, both contractor and engineer can, at any time, test the bottom of the ditch as to its depth and grade. Sides of Ditch. Smoothness of the sides of the ditch and the waste banks is not so important as regularity and symmetry of shape. The action of the water and weather will reduce the banks to the required smooth- ness provided there are no deep cavities or out-jutting earth left by the dipper. It should be observed in this connection that rough and ill-shaped ditches are often made by contractors on the plea that it is impracticable to make them otherwise with the machine they are using. This feature of the work, however, depends largely upon the care and skill exercised by the operator, but any special care of this kind requires more time and hence adds somewhat to the expense. Floating ma- chines do their excavating under water and in a general way keep the grade of the ditch by the length of the dipper handle beneath the surface of the water. The depth is checked from time to time by measurements from the grade-stakes which have been set along the berm by the engineer. Dry-land machines, that is those that operate from the surface of the ground, can be so manipulated as to make almost any desired side slope, and special slopes should be specified and insisted upon in land where the stability of the ditches requires their use. Flat slopes can be easily made where horses and traction engines are used as power, and the various forms of slip 226 ENGINEERING FOR LAND DRAINAGE scrapers and elevator graders are employed to do the work. The examination of the completed ditch should be made with the level and measuring tape, and a report be prepared setting forth the condition of the ditch and its conformity to the plans and specifications. Ditching Machines. Drainage ditches should be planned so that they can be excavated by machines. There are a number of types of these, each of which is adapted to its own class of work, the limitations and capabilities of which should be known to the engineer. The floating dipper-dredge is well-suited to the con- struction of large ditches where there is water in sufficient volume to float the barge which carries the machinery. Ordinarily, the smallest ditch that can be made with it is 15 feet wide on the bottom, though this depends upon the depth of ditch and upon the depth of water in it at the time of excavation. The dippers ordinarily used range from ^ yard to 2% yards. They are adapted to the excavation of ditches of 15 to 50 feet bottom width, and are now made of such strength that ditches through heavily wooded country can be excavated expeditiously and at moderate price. In such work, dynamite is used to shatter the large stumps, after which they are lifted out by the dipper and cast one side. The dredge is operated most cheaply downstream since the water follows and floats the barge. By making dams, however, to retain the water in sufficient quantity to float the dredge, it can be operated up grade. The combined floating and walking dipper-dredge is adapted to ditches as small as 15 feet bottom width, and is equipped with a walking device by means of which it can move itself across a level country at the rate of one mile a day. LOCATION AND CONSTRUCTION OF OPEN DITCHES 227 There is also the traction dipper-dredge, which moves over the surface on caterpillar or rough-belted wheels. This goes astride the ditch up grade, and with a ^ yard dipper completes as small a ditch as may be desired. The drag-excavator is another type which operates from the surface of the ground and takes its name from the type of bucket employed. The bucket is in the form of a slip-scraper and is filled in the same manner, then raised by a wire cable which passes over the end of a boom and thence to the winding drum operated by the engine. The bucket is then swung to one side and tripped. The machine may move on rollers placed on a track of timbers ahead of the ditch, or it may move on one side of the ditch. The buckets are made for this work as large as 2^ yards capacity. By means of a long boom it will deposit the earth at a greater distance from the ditch than a dipper-machine, and for that reason is adapted to the construction of levees and embank- ments, and can be used for large or small ditches wher- ever the ground is sufficiently stable to support the machine. Two other types of buckets known as the orange- peel and the clam-shell are fitted for excavating and moving material which is sufficiently soft to permit buckets of that class to be filled. The orange-peel is particularly useful in building levees. The ladder type of dredge works well in the excava- tion of loose and sandy earth, particularly where large ditches are required. The well-known hydraulic dredge is especially suited to large projects and to special work. These are the general types of machines which are in common and successful use for excavating large open ditches. The perfection of these several types has 228 ENGINEERING FOR LAND DRAINAGE made it possible for the engineer to carry out reclama- tion projects of great magnitude with thoroughness and reasonable dispatch. Compared with the imple- ments and methods which were available to engineers fifty years ago, progress in this direction has been remarkable. Specifications. A part of the engineer's service in connection with surveys and plans which he makes is to draw specifications for constructing the works. The contractor should know not only the character of the work upon which he tenders a bid, but the regulations under which he must perform the work. The engineer should be familiar with the contingents incident to construction in order to frame the specifications so that the work will be thoroughly and well done, and yet not entail needless hardship upon the contractor. While the stipulations which should be embodied in specifi- cations must be varied to meet the needs of different classes of work, the following memorandum of points that should be kept in view will be helpful. Relation of Engineer and Contractor. It is commonly required that the work be done under the direction oi the engineer, and according to the maps, plans and pro- files which are made a part of the specifications. The contractor shall use methods and appliances which in the judgment of the engineer will enable him to com- plete the work within the time and in the manner speci- fied. Subletting of Contract. Work shall not be sublet without the written consent of the engineer, and such action shall not relieve the contractor from his obliga- (ions for the satisfactory performance of the work. Change of Plan. It sometimes becomes advisable to change the plans after the contract has been let. Where such changes involve a difference of cost to the con- LOCATION AND CONSTRUCTION OF OPEN DITCHES 229 tractor they shall be agreed to by both parties to the contract, and the price of work required by the change of plans shall be based upon the price named in the contract. No claim should be allowed for extra work except upon the written order of the engineer. Risks and Delays. It is usually required that the contractor shall make no charge for delay on account of legal difficulties which may occur, or for the failure of any other contractor to do his work, but he shall be entitled to an extension of time in which to complete the contract. He shall assume all risks due to the weather or other unforeseen occurrences. Defective "Work and Damages. In case defective work is done the engineer may require the contractor to make it good, or, if in the engineer's judgment it is undesirable for any reason to do so, he may make such deductions from the price as he deems reasonable. The con- tractor should be held responsible for unnecessary damages to property through which the ditch is con- structed. Clearing Right of Way. In wooded country the price of excavation may be made to include clearing right of way for the ditch, or an additional price per lineal one-quarter mile, or other unit, may be allowed. In either case it should be stipulated who is to have the timber. Removing and replacing highway bridges and fences should be provided for. Usually this is required of the contractor. Berm and Side Slope of Ditches. A berm of not less than eight feet should be specified for ordinary work, and the side slopes designated should be such as will be required in the finished ditch. These will be gov- erned by the kind of land through which the ditch is to be made. Openings in the waste banks should be made for the entrance of tributary ditches and streams. 230 ENGINEERING FOR LAND DRAINAGE Inspection and Partial Payments. It is customary for the contractor to receive monthly payments of 75% or 80% of completed work upon the estimate of the engineer, the balance to be paid upon the completion of the con- tract. Survey Stakes. The stakes set by the engineer for the guidance of the contractor are an essential part of the specifications and must be followed, and as far as possible preserved, during the execution of the work. In general, it may be said that the more complete the plans have been made the more simple the specifications may be. A clause in the contract requiring the work to be done according to the plans will then eliminate many questions which would otherwise require adjustment as the work proceeds. Camping Outfits. Where an extended survey is to be made, either preliminary or location, it will be best to use a camp, moving it from point to point so that the men can be kept within convenient distance of the work as it proceeds. The following outfit will serve for a party of eight men, including a cook and teamster. 3 14' X 14' tents with 4' walls of 12 oz. army duck, with fly, poles and pins for each. I Steel box cooking range. I Doz. folding canvas cots. 1 Doz. folding stools. 2 Boxes of convenient size, one for provisions and one for table-ware. I Set light cooking utensils, three lanterns, supply of fly-netting and kitchen towels. I Set enameled or granite table-ware. Boards for a dining-table and for table seats. A small tent for office work can be added if desired. Each man furnislies Iiis own bedding and towels. The entire outfit should be as light as will be consistent with LOCATION AND CONSTRUCTION OF OPEN DITCHES 23 1 durability and strength, for the reason that the camp must be moved frequently, and the delay and labor in- cident to moving and setting up a heavy outfit, in- volves a considerable additional expense. If desirable, by a little crowding, two tents can be made to accom- modate a party of this size. CHAPTER XV PROBLEMS IN OPEN-DITCH WORK Curvature of Ditches. The proper curve to give ditches when they are deflected from a straight Hne is a matter which merits careful attention. It is desirable that the adjustment of curve to velocity of flow be such that the banks will not require artificial protection. The relation of bank erosion to curvature of the ditch and the velocity of flow is intricate, owing to the great difference in the stability of earth when subjected to the action of water. Circular curves are described by the number of de- grees of arc which a chord of loo feet subtends. The degree of a curve is determined by the central angle which is subtended by a chord of loo feet. The follow- ing is a table of curves and their corresponding radii which may be used as a basis in constructing ditches with limitation as hereafter described. TABLE XVI Curves and Radii Degree Radius in Ft. Degree Radius in Ft. 7 819 14 410 8 717 15 383 9 637 16 359 10 574 ^1 338 II 522 18 320 12 478 19 303 13 44a 20 288 232 PROBLEMS IN OPEN-DITCH WORK 233 While circular curves may be used to describe ap- proximately the curvature that should be given, the true form should not be geometrical, but rather what may be termed natural, or such as is used in laying out artificial streams and roads in parks, in which geometri- cal lines are ignored. The difference between the two is shown in Fig. 47, which is a 12-degree curve (radius 478 feet), so varied as to subject the bank against which the 300 ?ooi- FiG. 47. — Proper Curve for Open Ditches stream strikes, when first deflected, to the least possible erosion. The reason for this is well illustrated by Fig. 48, in which the stream is represented as being divided into filaments, each having a velocity imparted to it by the flow, and striking the opposite bank as an indi- vidual force. According to the well-known law of physics, the angles of incidence and reflection are equal when a force meets a resisting plane. Hence in the case under consideration, the reflected force is thrown against the other forces or filaments toward the interior 234 ENGINEERING FOR LAND DRAINAGE of the Stream and assists in breaking the force and de- flecting the current. The section of curve first struck would receive the greatest force, and be subject to greater erosion if the curve were a segment of a circle. For this reason the up-stream part of the curve should be deflected from the tangent by using a curve of greater radius than the remainder of the curve, in order that all parts may be subject to uniform erosion. When the points of tangency have been fixed upon, the curve may be "run in by the eye" better than by Ditch - Fig. 48 . — Action of Current on Ditch Banks at Curves. an instrument, and the center line located by measure- ments from the tangents in the manner shown in Fig. 47. How short a curve may be used in large ditches such as are constructed for drainage districts, without en- dangering the stability of the banks at the curve, is a question that can not be answered wjth mathematical certainty for the reasons previously stated. Deductions from close observations of both natural and artificial streams which flow through alluvia! soils are the only guides to the work. From such observations the fol- lowing empirical rules may be deduced: PROBLEMS IN OPEN-DITCH WORK 235 For ditches with minimum bottom width of 6 feet and maximum grade of 2 feet per mile, use 20-degree curve = radius of 288 feet. For ditches with bottom width 6 feet to 20 feet and grade of 3 feet to 6 feet per mile, use i2-degree curve = 478 feet. For larger ditches and greater fall, or for the above- named ditches with a greater fall than indicated, curves ranging between 6 degrees and 12 degrees may be used, with such latitude as conditions of earth and fall may suggest to the careful designer. Erosion. Injury to ditches by erosion occurs in two ways : by direct wearing away of the banks through the action of the water, which removes the particles of earth and carries them by suspension down stream; and by the action of water upon a stratum of earth in the bank more susceptible than the rest, thus undermining a por- tion of the bank, causing large masses to fall into the channel. The latter is the more destructive of the two and the more difficult to prevent. The eroding power of a stream increases directly as the square of the velocity; that is, the relative eroding power of two streams having velocities of 2 feet and 3 feet per second, respectively, is as 4 to 9. Since velocity varies directly as the square root of the rate of fall of the chan- nel, the eroding power varies as the fall of the stream; that is, it is twice as great on a stream with a fall of 4 feet per mile as on one with a grade of 2 feet per mile. This, of course, refers only to the wearing effect against a bank, but this law points out certain methods of dimin- ishing erosion and the consequent caving of the banks of a ditch or stream. Erosion may be lessened by widening the channel so that the depth of flow will be diminished and the con- sequent velocity reduced; by making the grade of the bottom as even as practicable; and by removing 236 ENGINEERING FOR LAND DRAINAGE obstructions from the center portion of the channel so that the velocity will be as uniform as it is possible to make it. These methods are applicable to general con- ditions, and should be regarded in designing ditches. Sometimes the side slopes may be made more flat, which will have the effect of reducing the velocity of flow along the sides of the channel. In case of large streams, wing dams or dikes can be used to deflect the current away from the banks and cause it to follow the center of the channel. Much trouble is experienced, in alluvial soils and others which erode easily, at points where lateral ditches enter the mains, particularly if the branch en- 100 KCt Fig. 49. — Proper Junction of Shallow and Deep Ditches. ters at a higher level by an overfall. The effect is to form a bar of silt just below the point where the branch enters, and to cause the branch ditch to erode badly for some distance up-stream. Much of this difficulty can be avoided by having the lateral ditches cut down to such a grade that the point of discharge will be at the bottom of the main. Provision should be made at all points where water discharges into open ditches to elim- inate all overfall or drop, unless such entrances are pro- tected by structures of timber or concrete. In Fig. 49 the line a b indicates how the grade of a shallow ditch should be changed to avoid the washing away of earth and consequent filling of the deeper ditch into which it PROBLEMS IN OPEN-DITCH WORK 237 empties that will occur if the branch is permitted to discharge on its regular grade by overfall. Decrease of Flow Due to Obstructions. The dif- ferences in flow and consequent discharge between channels in good physical condition and those in bad condition are much greater than is usually assumed. Ditches and watercourses often become obstructed by bars of silt, accumulations of brush, logs or other debris, and by jutting banks bearing clumps of bushes and trees, all of which detract materially from their carrying capacity. As before stated, the measure of these differ- ences is represented in Kutter's formula by the factor n, to which values corresponding to the roughness of the channel are assigned varying from .02 to .05 (See Value of n, Chap. XII). The effect of these variations upon the flow of a ditch 20 feet wide and 7 feet deep is that when n = .0225, the ditch- will carry 31% more than when n = .03, and 50% more than when n = .035. This emphasizes the importance of freeing a drainage channel from all obstructions possible, and of maintaining it in good condition. The possible betterment of the physi- cal conditions of an existing channel should receive first consideration where the general improvement of the drainage of a country is contemplated. Not infre- quently its effective capacity can be increased one-third by removing trees, brush and other obstructions which retard the flow and diminish the uniform sectional area of the channel. This is particularly true of streams 20 to 60 feet in width. Such improvements can be made at a cost far less than any other giving equal results. Cutting oflE Bends in Crooked Channels. A crooked channel may be greatly increased in carrying capacity by cutting across the bends in such a way that the water will flow in a fairly straight line down the valley, pro- vided the size of the channel throughout is properly ad- 238 ENGINEERIN-G FOR LAND DRAINAGE justed to the new conditions. The fall through a given valley being a fixed amount, it follows that the shortest line will have the greatest percent of grade and resulting velocity. If the channel through which the water flows is shortened to one-half its original length, the rate of fall will be doubled; since the velocity of flow in the same channel varies as the square root of the head or fall, the ratio in the above assumption would be the "s/ 1 to v 2 or I to 1. 41. If the channel is shortened to one-fourth Fig. 50. — Cutting Off Bends in Crooked Channels. its original length the velocity will be doubled, the size and other conditions of the channel remaining the same. This method of improvement should be consistent throughout the valley, otherwise the relief of one part of the stream may result in the congestion of the water and consequent overflow of lands in another. Let a b e f in Fig. so represent a crooked channel which by reason of its insufficient capacity causes overflow. If we elim- inate the bend b, by making the cutoff cd, the new channel will be only one-fourth as long as the old one, PROBLEMS IN OPEN-DITCH WORK 239 and the velocity of flow through it will be double thai through the old course. Unless the channel de has sufficient capacity to accommodate the increased flow, which in some instances is the case, it will be overcharged and overflow conditions will be increased along that part. For this reason it will be necessary to continue the straightening process down the stream and also pos- sibly to improve the original channel in order that the benefits of increased drainage facilities may be uniform along its course. The combined flow of the cutoff and bend may be utilized, but it should be understood that the channel at the junction of the two, as at d, should have a capacity sufficient to receive the combined flow. Waterway between Levees. The improvement of streams for the protection of overflowed bottom-lands often requires the construction of levees on each side of the channel, because the enlargement of the channel to sufficient dimensions to carry the entire quantity would be either impracticable or too expensive. The problem to be solved in such cases is to determine the height of the levees and the distance apart that they should be placed in order to meet the requirements. The volume of water which must be provided for should first be estimated. If there is some point on the stream where the volume has been gaged with approxi- mate accuracy, the result will assist in estimating the volume, in case the flow should be confined between levees, but even such measurements may easily mislead the engineer for the reason that the channel may overflow at points and fill up portions of the valley as it would a reservoir, so that the maximum flow does not represent that which would take place in a well-prepared channel. The better method of arriving at the amount is to estimate the runofif from the entire area by every means available, observing particularly the manner in which 240 ENGINEERING FOR LAND DRAINAGE the water comes into the main channel, that is whether it is brought by a few large tributaries from a consider- able distance, or by small short streams which discharge their contents quickly into the center of the valley. Having decided upon the number of second-feet that should be carried, estimate the capacity of the exist- ing channel and then, by trial, compute the capacity of a waterway between levees with assumed heights and at different distances apart until a channel has been found that will carry the required amount. In computing the capacity, the channel should be treated in three parts: the central or river-channel part,, and the two sides, where the water will be com- paratively shallow and the bottom more obstructed than that of the main channel. Let Fig. SI represent a stream which it is proposed to control by levees on each side. Using Kutter's for- mula, we first compute the discharge of the central channel, e b c f. The wet perimeter is abed, because e a and f d are water-surfaces and present little or no frictional resistance. The area of the waterway below h — _e / ■ "/-. mm^ ''^ _j^"*^^- - s^*' .'Si-^s^sss; ;\^^\. .sb-wv^^y ^^S^feS* ~~K Fig. 51. — Waterway Between Levees. and above the level of the land, that is, e b c f, di\-ided by the length of a b c d = r. The \alue of n will be per- haps .025. Having the slope of the \'alley, the discharge can be computed by substituting the proper quantities. The portion of the waterway on each side of the central channel may be regarded as two distinct parts, as the distance from the main channel to the levees is not always equal. The wet perimeter of f d h g, in the figure, PROBLEMS IN OPEN-DITCH WORK 24 1 is d h g since f d being water-surface may be disregarded. The value of r is then the area of f d h g divided by the length of d h g. The value of n for this part of the channel may be .035, or more, depending on the surface and obstructions in the side channel. The sum of the discharges of the central and two side channels will be the approximate total discharge of the assumed water- way. The levees should be built three feet higher than the estimated height of the water in the channel, and even a larger margin should be allowed if the volume of flow cannot be estimated closely. Effect of Weirs and Dams. The effect of a dam with a free outlet below it is to permanently raise the water- surface from the location of the dam up-stream to a point where the rise in the grade of the channel is equal to the height of the dam, plus the head or rise which will be required to overcome the frictional resistance to flow offered by the dam. The rise occasioned by the dam is less if it is located where the channel is broad, as that will diminish the height of the crest at the dam. The effect of removing the dam is to lower the plane of the stream the amount it was raised by the obstruction, and to that extent benefiting the drainage conditions of the land adjoining the pond which was caused by the dam. By reason of the backwater curve which exists on the surface of the water above obstructions of this class, the surface is sometimes 6 inches higher one-half mile above the dam than at its crest. As far as it re- lates to drainage, the dam is a local obstruction which does not aff'ect the flow of the stream above the upper point of rise occasioned by it, where the velocity is governed by the gradient and the physical conditions of the channel. Raised Outlets. It may be necessary to discharge the drainage of a large tract through a main ditch into 242 ENGINEERING FOR LAND DRAINAGE a shallow stream or a swamp from which the water dis- tributes itself and slowly disappears. The ditch has been made 7 or 8 feet deep, but the water m-ust be dis- charged into a channel which may be only 2 or 3 feet deep. The question arises whether under such circum- stances the ditch should be graded so as to deliver the water at the level of the shallow outlet, or whether it should be extended its full depth and then depend upon the water rising to the higher level for an ou.tlet. The latter method is the proper one as will be seen from the following explanation: Let hk. Fig. 52, be the bottom of a ditch 8 feet deep, carrying water 4 feet deep, the surface of which would be at 1 m if the flow were unobstructed. Let 1 g be the Fig. 52. — Raised Outlet. rise which the water must make in order to flow through a shallow channel two feet deep whose bottom is g n. The line g d represents the level above which the water must rise to flow away, the point d, the hydro- static limit, and a b, the depth of water which may flow through the outlet g s. The movement of water over g n is due to the relief which is afforded at g, and also to the "piling up" of water at p which extends up-stream for a distance, forming what is called the backwater curve. The entire column of water a c has a mean velocity due to a head which is the difference in level PROBLEMS IN OPEN-DITCH WORK 243 between t and r. If then the width and slope of the channel at g n be sufificient to take the discharge from the large channel flowing under a head due to surface slope, as before explained, the entire volume of water will flow away at a velocity due to that head. As the water meets the obstruction h g the part below the curve g c will have no velocity, while the velocity of the column of water from the bottom to the surface, represented by the line c a, will increase in some such manner as is shown by the arrows. The' form of the backwater curve, p r, varies with the slope of the stream and the volume of water it carries. The limit of length, and also the rise, in the backwater curve is small, as for example, in a stream of light grade, the former is two miles, in which distance there may be a rise of six inches. The important point to observe in constructing an outlet to a ditch under these conditions is to make it sufficiently wide to carry the estimated volume of flow. There will be a risk from sedimentation, but this will be diminished by making the outlet large in the manner suggested. It is needless to mention that the land affected by the backwater will receive little benefit. CHAPTER XVI DRAINAGE DISTRICTS A DRAINAGE district is an organization of the owners of land formed for the purpose of constructing and main- taining adequate drainage outlets whose cost shall be shared in proportion to the benefits derived. The kinds of land properly subject to such organiza- tion are swamps or wet lands, wholly or partially unre- claimed; farm lands which have insufficient outlets; lands in river and creek valleys which are subject to overflow; and coast and tidal lands subject to inunda- tion by the sea. The ultimate object of draining such lands is to fit them for the profitable production of crops, and whatever improvements may be demanded by an intelligent and cultured people. Such work consists of two parts; the public drainage, which is accomplished by the cooperation of all the owners in the construction of necessary outlets whose cost is assessed to the several parties in proportion as they are benefited, and the private, or individual, work which is required on each farm and for which the owner himself pays. Three areas are considered in the development of plans for the construction of public ditches; first, the entire watershed tributary to and including the land in the district; second, the district itself which is bene- fited and controlled by the organization; third, the individual farms of which the district is composed and for which the organization has been perfected. The work which is required may be the enlarging or straightening qi a watercourse by which a number of 244 DRAINAGE DISTRICTS 245 landowners will be mutually benefited; the construc- tion of an extensive system of outlet ditches; or the building of levees and sluices, and the installation of pumping plants; but the method of organization and the successive steps in the promotion of the project are the same. Drainage Laws. The formation and management of districts is provided for in most States by laws which direct in detail the steps which should be taken and give methods of procedure which must be closely followed in order to make the proceeding valid. These vary in the several States in many particulars, but the essen- tial features of a drainage law are: first, the right given to property owners under certain prescribed conditions to petition the proper authority for the construction of drains which will be of public benefit; second, pro- vision for making and collecting assessments to defray the cost of the work, and also for the appraisement and payment of damages to property incident to such con- struction; third, the establishment of the perpetual right of landowners included in the district to use the ditches or drains which are constructed ; fourth, author- ity under proper legal regulations to incur debt and sell bonds for obtaining money with which to perform the public part of the work. Survey- and Report. The law places surveys under the direction of a board or an ofificer of the law, with authority to order them, and to receive and pass upon the report of the engineer. Upon his appointment the engineer should make a preliminary examination of the territory covered by the petition, previously filed with the proper authority, and outline to the board the kind of survey which he recommends, together with its approximate cost. Such boards usually refer these matters to the judgment of the engineer, who should ex- 246 ENGINEERING FOR LAND DRAINAGE ercise great discretion, so that while no unnecessary work will be done and costs incurred, sufficient data will be secured for the development of the necessary plan. Suggestions in other chapters regarding preliminary location of surveys should be followed in this work. The report should be accompanied by a carefully pre- pared map showing the ownership and acreage of each tract of land in the district, together with such eleva- tions or contour lines and topographical symbols as will show the drainage needs of each, the location of rail- roads, inter-urban lines and public highways crossing the district, and the proposed location of the ditches. The report should state the manner in which the latter will benefit the lands, and the general advantages which will accrue to the district as a whole. Estimate of Costs. Drainage laws usually specify that the petition should not be granted unless it is shown that the benefits which will accrue from the proposed work will be greater than its cost, hence before assess- ments can be made or active operations commenced the engineer must prepare a detailed estimate of the cost of the contemplated work, covering the following points: (a) the construction of the drains, which in- cludes excavation, such tile as may be required, the construction of any surface-inlets that may be needed, and the removal and replacing of highway bridges if the law requires this done by the district; (b) damages, which include the cost of right of way for drains or ditches, the construction of necessary bridges on rail- roads, highways, or farm lands, and amounts paid by reason of injury or inconvenience to private fields, or to roads and railroads; (c) ihc cost of engineering super- intendence, and fees of commissioners; (d) legal ex- penses arising from necessary attorney's fees and those due to suits which may be carried to court. DRAINAGE DISTRICTS 247 Appraisal of Damages. The law usually requires that damages shall be awarded by a commission appointed for that purpose, some of the States specifying that this board and the one to assess benefits shall be entirely distinct in their personnel and deliberations. In any case the consideration of damages is conducted regard- less of benefits, the two not being allowed to offset each other, but the damages are awarded and paid and the amount added to the total cost without reference to the assessment of benefits. When the outlet drain is an open ditch, the chief damages are the value of the land for right of way. Opinions and practice difTer as to the basis of valuation for such area, some holding that its selling price at the time of appraisal should constitute the amount of dam- age awarded, on the ground that giving the land for the ditch is the same as selling it. Others consider that if the land occupied by the ditch would be tillable when drained, its value under the improved conditions should be the basis of award, because the owner loses land that would have been rendered valuable if the ditch had chanced to run on his neighbor's side of the fence. These claim that giving the land for the ditch is not comparable to voluntary sale of it for the reason that in the majority of cases the owner would prefer to pay the cost of improvement and retain the land than be obliged to give it up. If the course of the ditch is a natural waterway and would not be tillable land under improved conditions, then only the value of such tillable land as is occupied by berm and waste banks or in straightening the course of the natural channel should constitute the damages. Minor damages may be awarded because of extra time and labor required annually owing to inconvenient divi- sion of fields by the ditch, or because it runs through 248 ENGINEERING FOR LAND DRAINAGE farm yards, or too close to buildings, or through pas- tures or fields where it must be fenced to keep live-stock away. Small corners or parcels of land so cut off by the ditch as to be of little or no value for cultivation or use should be paid for by the district. An illustra- tion of such a case is seen at the north end of G's farm on the map. Fig. 53, where the ditch cuts off a sharp corner between the highway and railroad. Necessary farm bridges are usually built by the district and in- cluded in the total cost. If done at private expense they are considered as damages. If the outlet ditch is a tile-drain, then right-of-way privileges and the cost of crops destroyed or whose planting at the proper season is prevented are the only damages allowed, as an under-drain is no injury to the land. In some States the law makes it incumbent upon the injured party to claim damages within a specified time, and, if he fails to do this, no damages are awarded. It would seem more just to award damages to all im- partially, as benefits are assessed, without requiring claims to be filed. Highways are also claimants for damages. Where towns construct that part of outlet ditches crossing public roads, the cost of the construction is regarded as damages due the township road fund from the dis- trict. A ditch along a roadway obstructs travel and inconveniences the traveling public during its construc- tion. If the excavated material is thrown on the road- bed, extra labor is required to so level and compact it as to make the road fit for use. Often a temporary side- road must be provided to accommodate travel. All of these and other similar exigencies give occasion for just damage claims. Railroads are allowed damages for the cost of con- DRAINAGE DISTRICTS 249 struction of district ditches across their rights of way. New bridges or the substitution of a new one for an old one made necessary by the increased volume of water, present a situation over which there are contentions between railroads and districts, the former holding that districts should pay for a new bridge, or in the case of substitution, the difference in valuation and cost of erection of the two bridges, while the latter hold that the railroad must provide at its own expense what- ever bridges are needed to permit the passage under them of all water that may by reasonable and lawful drainage be brought to them, the district only paying for the cost of construction of the channel. A Supreme Court decision in at least one instance where appeal was taken sustains this latter contention. The engineer may not be directly concerned in the award of damages, but he should keep in close touch with the situation, and be so familiar with the law and with the court decisions in drainage cases that he can make helpful and pertinent suggestions which may materially expedite matters or prevent injustice. Assessments of Benefits. It is distinctly stated in most drainage laws that assessments upon property for defraying the cost of the work should be in proportion to the benefits conferred. After the cost of the work has been sufficiently determined to show that it will be well below the resulting benefits, such assessment should be made. The manner of doing this is usually left to the judgment of a board whose appointment is prescribed by law and whose duty it is to assess the benefits to each landowner. The engineer is frequently a member of this board and in a position to largely direct the adjust- ment of the assessments, but if not, he is almost certain to be called upon to assist in the performance of the task. Having been identified with the survey and 250 ENGINEERING FOR LAND DRAINAGE famijiar with the lands, he should be able to give infor- mation which is essential in the consideration of this delicate question, while his training and experience should render his judgment and advice sound and trustworthy. He should enter upon the work not 6nly with a desire to be as fair and impartial as possible, but with a thorough understanding of the principles involved in an equitable assessment, and a knowledge of the absolute and relative values of the factors upon which his judgment must rest. A hasty or superficial per- formance may result in gross injustice and lead to serious delays and legal entanglements. Principles Underlying Assessments. The following principles which apply in the determination of assess- ments upon various properties should not be overlooked by those who are appointed to perform this duty. An owner is entitled by right of ownership to such natural drainage as his land possesses, and may drain it as he chooses provided he does it within the boun- dary of his own possessions and discharges his artificial drains into a natural watercourse on his own land. If the natural outlet for the territory surrounding him is upon his land, he should not be assessed for any part of the cost of cooperative drainage unless it can be shown that he is benefited by the drainage of the adjoining land. If, for example, the slope of the country is such that without the drainage works he would ha\e to take care of the natural drainage of one or more farms above him, of which he is relie\cd by the construction of the artificial outlet and the drainage of these farms, then the public works will benefit him to a degree depending upon the injury he sufforod by reason of the wet condi- tion of the adjoining land. An illustration of this is seen in the case of H in the assumed district. (See Map and Memorandum, Drainage District No. 4, pp. 268 and 269, DRAINAGE DISTRICTS 25 1 Although the natural outlet is on his land and it is plain that he could have drained without the coopera- tion of his neighbors, his assessment is quite high. But the slope of the land is such that he receives the drain- age of the farms above him. Had not the district drain relieved him, his private drains must have been large and costly to take care of the water discharged upon his land. The outlet ditch and the drains of his neighbors will relieve him to such an extent that the cost of his private drainage will be greatly lessened. For this reason it is fair to make his assessment as high as the wetness of his land calls for, notwithstanding his near- ness to the outlet. If no such condition exists, and no other benefit is apparent, no assessment should be made against him, while damages should, of course, be awarded for the right of way to the outlet on his land. The law pro- vides that such right of way cannot be withheld from a district, but in case no agreement with the owner can be reached, the necessary land may be condemned and the proper remuneration awarded by jury. A tract of land which is wet and practically useless for agricultural purposes should be assessed propor- tionately higher if reclaimed by the drainage system than other land in the district which has better natural drainage. Other things being equal, the greater the injury to the land from water, the higher should be the assessment if it is fully reclaimed. A tract which lies distant from a natural outlet may be assessed higher than one lying near, if both receive the same drainage advantages, on the ground that the former has had brought within its reach by the construction of the artificial outlet what the latter pos- sessed without it, but only when such land has little or no natural drainage. 252 ENGINEERING FOR LAND DRAINAGE Outlet privileges should be assessed in proportion to the distance of the lands from the ditch, as upon that will depend the length of lines and consequent cost of private drains to • complete the drainage. In case a public drain incidentally passes through a farm for the purpose of giving more perfect drainage privileges to adjoining land, and in so doing affords direct drainage to the farm, and also lessens the expense which will be required to complete its drainage, the farm should be assessed proportionately higher than the land adjoining because private drainage has been accomplished at public expense. If a drainage district does not furnish complete out- let for the lands of the entire tract, those which receive only partial drainage should be assessed proportion- ately less. If within the limits of a district are soils of widely differing fertility, some of which are capable of pro- ducing high-priced market-garden crops, while others have but little or medium fertility, the fertile lands, other things being equal, should be assessed the highest, because the value of the drainage is greater to such land. The land occupied by right of way should not be assessed for benefits as it will yield its owner no future returns, but the number of acres so used on each prop- erty should be deducted from the total acreage of that property and not appear on the assessment sheet. How- ever, while this is correct in principle, the amounts in- volved, except in costly improvements and large indi- vidual holdings, are so small that this point is usually ignored. Methods of Assessing Benefits. In this important part of organized drainage operations, it is desirable that a general sdieme or plan be followed in order that equitable ratios of benefit shall be securgd for all lands DRAINAGE DISTRICTS 253 throughout the district. Current practice in this varies greatly, and the principles underlying each method should be studied critically before deciding upon the one best adapted to the case in hand. The value of any method, however, depends largely upon the judg- ment of those using it. Drainage Districts organized under the State laws are permitted to issue interest-bearing bonds to provide funds to finance the work, and the assessed property in the District becomes security for the payment of the bonds and the accrued interest. Where this is done the benefits must be definitely assessed and should be about twice the estimated cost of the work since the measure of benefits fixes the limit of the tax that can be levied, and bond buyers demand a safe margin for security of the bonds. A brief description of the principal methods employed in assessing the benefits are here given. Some of the State laws prescribe the method which shall be used; in other States the Assessment Board is left free to choose its own method. The first three methods mentioned apply to the distribution of cost without any assessment of benefits other than determining in a general way that the benefits will exceed the cost. Arbitrary Assessment of Cost. By this method the cost of the improvement having been estimated and found to be less than the benefits that will accrue, the amount of cost that should be assessed against each property is determined by the board or oiScer of the law appointed for the duty, by inspection, comparison, and trial, the endeavor being to proportion the assessment of costs to the benefits. In practice, the estimated average cost per acre of the proposed improvement is taken as a basis, and changes above or below this amount are made to correspond with the variations in benefit which 254 ENGINEERING FOR LAND DRAINAGE will be conferred upon each property. In case the amount levied is not sufficient, a second assessment is made upon the same basis; if the amount is too great, a rebate is distributed. This is the oldest method of making special assessments, and in the hands of a well-informed board that will canvass the entire situation carefully, gives satisfactory results for small districts where bonds are not issued. If the examination is superficial or the members of the board do not understand the benefits accruing from the construction of drains, unjust assessments may be made. Assessment of Cost According to Value of Property, or Ad Valorem. Assessments made in this manner assume that the improvement is of a public nature, and that its cost should be provided for in the same manner as other taxes. Assessments for the cost of levees are some- times made upon this basis on the theory that the benefit of the improvement is in proportion to the value of the property protected. A Flat Rate or Uniform Charge per Acre. Such an assess- ment is sometimes made upon the lands of an entire dis- trict when the benefits of the improvement are fairly uniform, as may be the case on lands where a levee is constructed to protect them from inundation by tide or river; or where a natural stream is improved in such a manner as to uniformly benefit the lands of an entire valley. In the following methods the benefits are more or less definitely assessed upon each tract of land, and the cost distributed proportionately. In some cases simply a ratio is established according to benefit by which the cost is apportioned, but the placing of a money value upon the benefits assessed is practically required by some State laws, and has advantages which are bringing DRAINAGE DISTRICTS 255 it into favor with engineers and Assessment Boards even when not so required. Difference in Value Before and After the Improvement. In this method of assessing the benefits the value of the properties before and after the public drain has been constructed is estimated and their difference is made the basis of the assessment. A tract of land estimated worth $1,000 before drainage and $i,8oo after, is assessed $800 benefit, and if the cost of the work is one-fourth of the total benefit, it pays $200 as its proportion of cost. The difficulty in applying this method, particularly in a large district, is in making uniform and equitable valua- tions throughout, and in anticipating the increase in value which will result directly from drainage. In work- ing out the method, the total cost to be distributed is divided by the total estimated benefits. The result is the amount which each dollar of benefit costs. The estimated amount of benefit to each property multi- plied by this quotient gives the total cost each pays. This method is worked out on the Assessment Sheet of Drainage District No. i, page 256. Distribution of Cost by Division of Land into Classes. Several State laws specify that the lands shall be divided into five classes (in one instance, three), in which the benefits per acre shall be represented in the ratio of 5, 4, 3, 2 and I. The classes are designated as A, B, C, D and E, and in the distribution of cost, lands in Class A pay $5.00 per acre when those in B pay $4.00, C, $3.00, D, $2.00, and E, $1.00. These laws do not require an assessment of benefits, but the district may be estab- lished by the board of commissioners after they have satisfactory evidence that the benefits in general will __exceed the cost and that the work will be conducive to the public welfare. It is advisable, however, to esti- mate the benefits, and the sale of bonds will be greatly 256 ENGINEERING FOR LAND DRAINAGE DRAINAGE DISTRICT NO. 1 Assessment Sheet Value Before and After Drainage 1 2 De- scrip- tion of Land 3 Num- ber of Acres 4 Valuation. 5 Assessment of Benefits in Dollars 6 (Left blank by Assessor) Apportionment OF Cost. $0.24=Cost of $1 of Benefit. Owner (a) Before (b) After (c) Per Tract (d) Per .Acre. A B C D E F 8o 120 i6o 40 i8o 6o 2 town lots S800.OO 3,600.00 3,200.00 1,600.00 4,500.00 600.00 300.00 $4,000.00 7,200.00 8,800.00 2,400.00 9,000.00 3,000.00 420.00 $3,200.00 3,600.00 5,600.00 800.00 4,500.00 2,400.00 120.00 $768.00 864.00 1,344-00 192.00 1,080.00 576.00 28.80 $9.60 7.20 840 4.80 6.00 9.60 14.40 (each lot) Total . 640 acres $4,852.80 S48S2^o ^ J (,„^j of |i of Benefit 20220 Total cost of improvement Highways Landowners Average cost per acre to Landowners $S,ioo.oo 247.20 $4,852.80 754 DRAINAGE DISTRICTS 257 Class A : DRAINAGE DISTRICT NO. 2 Assessment Sheet Lands Divided into Classes. : S- Class B = 4. Class C = 3- Class D'= 2. Class E = i. 1 2 De- scrip- tion of Land 3 Number of Acres 4 Classification 6 Equivalent Number of Acres in Class E 6 (Left blank by Assessor) Apportion- Owners (a) Class (b) Ratio ment of Cost $.94 = Cost of Improvement to I acre of Class E M 80 160 60 20 A C E 5 3 I 400 180 20 $376.00 169.20 18.80 N 100 185 25 60 A B D 5 4 2 500 100 120 470.00 94.00 112.80 R 200 -.„ 100 **» 80 60 B C D E 4 3 2 I 800 300 160 60 752-00 282.00 150.40 56.40 S -r C E 3 I 300 60 282.00 56.40 Total. 945 3,000 $2,820.00 $2820 3000 = $.94 = Cost of Improvement to i acre of Class E c' Total cost of improvements $3,200.00 Highways, 5 per cent 160.00 Town Lots 220.00 380.00 Landowners $2,820.00 Cost per acre: Class A, S4.70; B, $3.76; C, $2.82; D, $i.8S; K, $.94 Average cost per acre to Landowners, $3.00. 258 ENGINEERING FOR LAND DRAINAGE facilitated when this is definitely done. The method is fairly well adapted to some lands, but lacks elasticity, because the variation of benefits conferred is frequently greater than can be indicated by only three or five classes, and injustice is done those whose benefits are less than a third or fifth of the maximum. Additional classes to accommodate a greater variety of degrees of benefit may be introduced when not prohibited by law, and the results worked out in the same manner. Before the lands in the district can be assigned to their proper classes, the location and kind of drains, and their relation to each tract of land must be deter- mined and a map prepared on which these are clearly indicated. The wetness of land in each tract, its com- pleteness of outlet and proximity to the ditch should be considered, with any other factors, such as fertility of soil or distance from a natural outlet, which should have weight in the particular district in question. An assessment sheet for an assumed district, Drain- age District No. 2, is given on page 257 to illustrate this method. The product of the number of acres in a tract by the ratio of the classes to which it has been assigned, gives an equivalent number of acres in Class E, or with a ratio of one. When the estimated cost of the project is known deduct any lump sum assessments there may be and divide the remainder by the sum total of Column 5 and the quotient will be the cost of the improvement to one acre of Class E, by using which as a multiple throughout Column 5 the cost is properly distributed to each tract (Column 6). If it is desired to express the estimated benefit in dollars, a definite ^'alue may be given benefit per acre to land with a ratio of s, and a column prepared after the manner of Column 5 on Assess- ment Sheet of Drainage District Wo. 4, and substituted for DRAINAGE DISTRICTS 259 Column 5 on this sheet, the multiple then used in filling the Cost column being the quotient obtained by divid- ing the total cost by the sum total of division (b) of the substituted column. Classification by Comparison, on a Basis of 100. The requirement made by the drainage laws in some States that the estimated benefits from the proposed drainage to each tract of land shall be expressed in definite sums in order that the excess of benefit above cost be shown, is not recognized in this system of classification. The drainage district is considered a quasi-public organiza- tion, and benefits upon which the establishment of the district depends should be estimated in the aggregate. In prosecuting a work of this nature some interests may be benefited but little or not at all, yet the aggregate advantages may fully warrant the undertaking. Classification of land on a basis of 100, as required in some State laws, is as follows: Select the farm, 40-acre tract or any other representative unit which receives the maximum benefit by reason of the proposed improve- ment, and indicate its classification, as well as that of other tracts equally benefited, by 100. Compare all other tracts in the district with this and rate each according to the relative benefit it will receive com- pared with the one marked 100. The various factors composing the benefit are taken into account, ag in other methods, and also a map prepared. With this in hand, those appointed to classify the lands examine the ground critically and record the ratio of each tract before leaving it. The members of the board form their judgments independently and then, while still on the ground, compare their markings, and review conditions, if necessary, until they agree on a classification that they believe will be equitable and just. 26o ENGINEERING FOR LAND DRAINAGE The assessment sheet for a district prepared by this method is shown for Drainage District No. 3, page 262- In this assumed case the land is divided into 40-acre tracts as required by some State laws, and there being no fractional tracts, size does not enter into the compari- son, and the column of classification represents also the units of benefit, thus simplifying the computations. It is not necessary, in order to apportion the cost, to give any value to the units of benefit, though this may be done as in other methods. The cost of a unit, which is compara- tively large because for 40-acre tracts, is found by dividing the cost of the improvement after deducting lump sums, by the sum total of the units of benefit. If bonds are to be issued, it will be desirable, and per- haps necessary, to give a definite value to benefit per 40- acre tract on lands graded 100, and prepare a column after the manner of (b) , Column 5, on Assessment Sheet of Drainage District No. 4, and insert between Columns 4 and 5 on this sheet, the multiple then used in filling the Cost column being the quotient obtained by dividing the total cost by the sum total of the inserted column. If tracts of land unequal in size are compared, a column must be introduced between Columns 4 and 5 which shall contain the product of the ratios, Column 4, by the number of acres in each tract, from which the cost is apportioned as before, by multipl>'ing throughout by the quotient arising from dividing the total cost after deducting lump sums, by the sum total of this inserted column. Assessment According to Percent of Benefit. This method is the most recent, but the most scientific and systematic, and it is believed, when rightly applied, gives the fairest results. It has been adopted by many of the best engineers, and its use is recommended whenever another method is not prescribed by law. The estimated degree DRAINAGE DISTRICTS 261 of benefit which each tract receives is here made the basis of the apportionment of cost, lOO per cent repre- senting the maximum in the district, and o the absence of all benefit. The different factors of benefit, which have more or less weight in all the methods in the determination of relative benefits, are here given a more definite and important place, being taken up separately and assigned a percent which indicates the proportion of maximum benefit that each tract receives under that factor in the judgment of the engineer or board. The several per- cents of each tract are then multiplied together to form its total percent of benefit. For example, natural wetness of land and completeness of outlet afforded by the ditch are factors of benefit. A tract may be marked 60 per cent under the first, and 80 per cent under the second, which expresses the judg- ment of the assessor that it receives only 60 per cent of the maximum benefit under wetness and 80 per cent under completeness of outlet, making the total benefit 80 per cent of 60 per cent, or 48 per cent of maximum benefit. The method is an attempt to reduce assessments or benefits as far as possible to an analytical process. If used with good judgment it gives equitable and satis- factory results. It will at times, perhaps, be found difficult to express all benefits by definite factors in such a manner that the ratio of benefit can be worked out with arithmetical precision. It enables the assessor, however, to treat the subject systematically and keep before the mind the principles that should be applied in every case. As conditions are seldom alike in any two districts, no hard and fast rule can be followed. Since the factors constituting benefit are not the same in all districts, their determination should be a subject 262 ENGINEERING FOR LAND DRAINAGE DRAINAGE DISTRICT NO. 3 Assessment Sheet Classification by Comparison. Maximum loo. 1 Z 3 4 Classifica- 5 (Left blank by Assessor) Apportionment of Cost Description Number tion; also $2.25 = Cost of I Unit Owners of Land of Acres. Units of Benefit of Benefit Per Tract Per Acre 40 100 S225.OO S5-63 K 130 40 80 180.00 4-So 40 60 135-00 338 40 40 90.00 2.25 40 90 202.50 S-06 L 200 40 90 202.50 5-06 40 25 56-25 1. 41 40 IS 3-38 .84 O 40 80 180.00 4-SO 40 35 78.7s 1-97 P 160 40 5 «-^5 .28 40 75 168.75 4.22 40 20 45-00 1.12 T 80 40 50 112.50 2.81 40 25 56.25 141 40 10 22.50 -56 40 60 I3S-00 3-38 W 240 40 100 225.00 5-63 ''*" 40 100 225.00 5-63 40 80 180.00 4-50 40 60 13500 3-38 Total . 840 1,200 $2,700.00 i32S2 _ f2.is = Cost of I Unit of Benefit. 1200 Total cost of improTements $3,100.00 Highways, 6 per cent fi86.oo Railroads 314.00 '400.00 Landowners $2,700.00 Average cost per acre to Landowners, $3.31. DRAINAGE DISTRICTS 263 DRAINAGE DISTRICT NO. Assessment Sheet According to Percent of Benefit (See Fig. 53.) 1 Owners 2 De- scrip- tion of Land 8 Number of Acres 4 Per- cent of Benefit per Acre 6 Assessment of Benefit in Dollars 100 per cent = J20 per Acre 6 (Left blank by Asses'r) Apportionment of Cost J.I5S = Cost of Ji of Benefit (a) (b) (0 (d) Per Acre Per Tract Per Tract Per Acre A 80 .140 $2.80 $224 . 00 $34-72 $ .43 B 380 90 70 60 .900 •405 .128 18.00 8.10 2.56 1,620.00 567 • 00 153 60 251.10 87.88 23.81 2-79 I-2S •39 C 130 20 SO 50 .900 .637 .130 18.00 12.74 2.60 360.00 637 . 00 130.00 55-80 98.73 20.15 2-79 1.97 -40 D 160 40 20 I. 000 .648 .204 .120 20.00 12.96 4.08 2.40 800 . 00 777.60 163.20 48.00 124.00 120.53 25 30 7-44 3 10 2.01 -63 -37 E 200 80 60 50 10 .900 .640 .240 .130 18.00 12.80 4.80 2.60 1,440.00 768 . 00 240 . 00 26.00 223 . 20 119.04 37 20 4-03 2.79 1.98 •74 .40 F 240 70 140 30 .900 ■499 •156 18.00 9.98 312 1,260.00 1,397.20 93.60 195 30 216.57 14-51 2.79 1-55 •48 G 300 150 75 75 .900 .720 .256 18.00 14.40 5.12 2,700 . 00 1,080.00 384 . 00 418-50 167.40 59-52 2.79 2.23 -79 H 280 90 100 80 10 .800 .641 .292 .176 16.00 12.82 5 84 352 1,440.00 1,282.00 467 . 20 35-20 223 . 20 198.71 72.42 5-46 2.48 I 99 90 -55 Total . 1,600 $18,094.05 $2,800.00+ J2800 = l.iSS = Cost of $1 of Benefit 18C94.05 Total cost of improvements $3,200.00 Highways, 5 per cent f 160.00 Railroads 240.00 400.00 Landowners $2|Soo.oo Average cost per acre to Landowners, $1.75. 264 ENGINEERING FOR LAND DRAINAGE of especial consideration. Besides this, the weight each should receive varies, thereby necessitating particular care in assigning the percents of value to each so that their effect on the total shall be relatively equitable and correct. It may be observed that certain factors are component parts of the benefit. They are wetness of land, which determines the need of drainage; proximity to the drain, which determines the cost of additional drains to com- plete the drainage; completeness of outlet, which deter- mines the degree of thoroughness of drainage made possible by the district outlet drains; and the fertility of the soil, which affects the value of the improvement to each tract. To these may be added, distance from a natu- ral outlet, which affects in a minor degree the need of the improvement; and difference in location, which affects the degree of benefit, as in the case of lands which are near a town or city and by reason of this may become resi- dence or factory sites, while others have only country surroundings: these and other factors may or may not 2nter into the final estimate of benefits. In determining the weight of a factor it should be noted that o per cent does not mean the lowest degree of benefit which may exist in the district, but the entire absence of benefit. In the case of j)roximity to the drain, for instance, those lands farthest distant should not be rated o, for it is evident that their benefit is still consider- able. In this regard only lands entirely out of the dis- trict can be said to receive no benefit. Those near the border of the district may perhaps properly receive from 50 to 60 per cent by reason of proximity to drain, making the range of this factor only between 50 and 100 per cent. Distance from a natural outlet, when it enters as a factor, should not be given a wide range. Except in districts vhosc upper part is so level as to have little or no natural DRAINAGE DISTRICTS 265 drainage the benefit received by the upper lands, in having the outlet brought within reach,, is practically offset by the benefit received by those at the lower end in being relieved of the water from lands lying above them, and distance from the outlet should not be con- sidered a factor. In the case of fertility of soil, it is possible that there will be a tract in the district which is entirely devoid of fertility and should be rated at o, in which case the total percent of benefit to that land would be reduced to o. But other lands in the district may vary so little from the maximum in this respect that 80 to lOO per cent would fairly represent the range. Under wetness of land a tract may be given a o rating if by any chance one requiring no drainage falls within the district. This rarely occurs and the minimum bene- fit does not usually fall below 20 per cent or 10 per cent at the least, though lands with the maximum wetness are found in every district. Completeness of outlet, also designated as thorough- ness of drainage, refers to the capacity and depth of the ditch with reference to its efficiency as an outlet to the lands it serves. District plans do not always pro- vide outlets that will fully meet the needs of every tract. It is not common for this factor to become o, because some relief will usually be given even by a defective out- let, while it should be possible, ordinarily, to give the maximum rating of 100 per cent to all lands in well- designed districts. Benefits in this particular may, however, range from 100 per cent to 50 per cent, and possibly lower, observing that a few intermediates will express varying degrees of benefit as closely as it is possible to estimate them. In regard to the whole question of range which should be given each factor, and the latter's consequent weight 266 ENGINEERING FOR LAND DRAINAGE in the total estimate of benefit, it may be suggested that in order to determine this in any doubtful case, consider a supposed or actual situation in which all other factors are lOO, and judge what is the least degree of benefit lands in the district under consideration should be con- sidered to receive if controlled by this factor alone. For instance, if fertility is the factor in question, consider a tract of land having the least fertile soil in the district, and determine what proportion of maximum benefit it receives from the improvement if all other factors are lOO. This v/ill establish a minimum percent for this factor in this district. A practical way to learn the efTect of different weights in factors, or changes in factor percents, is by trial on a real or assumed district. Experiment at length by varying the range of factors and altering the percents, being careful to compare results and note how the total percent is affected. This will assist one to intelligently adjust the weights of the factors and determine the just factor percents. It may be found that in order to properly meet special cases where local conditions demand it, some small addi- tions to or subtractions from the total percent obtained by multiplication of the factor percents, will be necessary. This discussion will serve to show the difficulties and dangers in reducing assessment of benefits to a strict arithmetical process. As before said, the practical \'alue of the method depends upon the amount of judgment and common sense exercised in its use. It must not be so rigidly carried out as to sacrifice in any degree the rights of the landowners. As in all other methods, too much emphasis cannot be placed upon the importance of performing the work on the field, and not in the office. It is only through actual knowledge of existing conditions gained from personal DRAINAGE DISTRICTS 267 reconnoissance and inspection of the entire district, tiiat justice can be even approximated. The percents of benefit under each factor should be assigned on the ground, with a map of the proposed work at hand as a necessary part of the field equipment, for from it the relative elevations of the surface and bottoms of the drains, as well as the distance of the several tracts from their outlets are obtained, and these are necessary points in deciding upon the percents. The Assessment Sheet for Drainage District No. 4, page 263, illustrates this method. The percents under each factor are not shown on this, as it is preferable to omit them on the Assessment Sheet filed for public inspection because liable to be confusing or lead to unprofitable dis- cussion. They are given as a private Memorandum, page 269, and in connection with the map. Fig. 53. show how Column 4 is obtained. Only three factors seem to call for consideration in this small district. Complete outlet is provided for all the land, so that factor need not enter, as it would be i.oo throughout. There is quite a fall from the upper to the lower end and the benefits received by those at the upper end are thus well balanced by others received by those at the lower end, and the dis- tance from naturaloutlet can therefore be ignored. A definite value is given the estimated benefits on this Assessment Sheet as required by some laws, as almost necessary when bonds are to be issued, and as desirable in all cases. If, however, it is desired for any reason to apportion the cost without assessing the benefits in dollars, it may be done by substituting for Column 5 of this Sheet, a column found by multiplying the amounts in Column 4 by the number of acres in each tract. The cost, $2,800, divided by the sum total of the substituted column, 904.68, gives $3.10, which, used as a multiple throughout that column, will apportion the cost to each 268 ENGINEERING FOR LAND DRAINAGE \ Sandy \^_Jfe— "^ -<*-ll-s=\ - -*- j«i_-*4\^j. H^-^-^:*^\ 220 acres s /^ 90 acr^4^\ 60 ac. *R.to-A- n^'^* \'^\ 70 ac. \ Mil V j41i— -^a- 120 acres 50 ac. /^ ^„ / 200ya^sir=z^ 50 ac; /jf,. ----'—- /f / 60 ac/— Fig. 53.— Map of Drainage District No. 4. DRAINAGE DISTRICTS MEMORANDUM 269 (See Fig 53 .) 1 a 3 4 Classification According to Percent of Benefit De- scrip- tion of Land Number of Acres Owner (a) Wetness (b) Proximity to Drain (c) Fertility (d) Total Percent Per Acre A 80 .25 X .70 X .80 = .140 90 1. 00 X .90 X 1 .00 = .900 B 220 70 •50 X .90 X .90 = .405 60 .20 X .80 X .80 = .128 20 1. 00 X .90 X 1. 00 = .900 C 120 50 •"S X .85 X 1. 00 = -637 50 •25 X .6s X .80 = .130 40 1. 00 X 1. 00 X 1.00 = 1.000 D Ifin ^° .80 X .90 X .90 = .648 loO 40 .30 X .80 X .85 = .204 20 .20 X .75 •X .80 = .120 80 1. 00 X .90 X 1. 00 = .900 E 60 .80 X .80 X 1.00 = .640 300 so .40 X .75 X .80 = .240 ID •25 X .65 X .80 = .130 70 1. 00 X .90 X 1. 00 = .900 F 240 140 .70 X .75 X .95 = .499 30 •30 X .6s X .80 = .156 150 1. 00 X .90 X 1.00 = .900 G 300 75 .80 X .90 X 1. 00 = 0720 75 .40 X .80 X .80 = .256 90 1. 00 X .80 X 1. 00 = .800 H 100 280 „ 80 .90 •50 X .75 X .65 X .95 X .90 = .641 = .292 10 .40 X .55 X .80 = .176 270 ENGINEERING FOR LAND DRAINAGE landowner, as under (c), Column 6, of the Assessment Sheet. It will be understood in all the Assessment Sheets, that the last two columns, the apportionment of cost, are filled in later by the proper ofificial, and form no part of the assessment of benefits. The work of the Assessment Board ends with the assessment of bene- fits in some form from which the cost, when known or estimated, can be correctly apportioned. The Column, Cost per Acre is not necessary, but is of interest. Assessment of Irrigated Lands. Where the territory in- cluded in drainage districts is irrigated land, the origin or cause of wet, or seeped, lands should be taken into account. In such localities the necessity for draining is due to water coming to them by percolation through the soil and by waste over the surface from adjoining higher lands, such water having been applied for irrigation. It is held by many in the irrigated sections that while the owners of higher lands are in no way benefited by the drainage of those lower, they are responsible for the con- dition of the latter, and should be assessed for a part of the expense, because the water which passes from the higher lands is brought to them by artificial instead of by natural agencies. This proposition is agreed to in some instances, and a part of the cost of draining the lower lands is assessed against the higher. The prin- ciple is generally recognized, howe\'er, that the holders of the lands requiring drainage must protect themseh^es against the seepage and waste of those which by nature occupy a dominant position. Actual benefits from draining a wet tract often extend to lands on a lower level, but quite distant from it. This is due to the interception of the seepage which would otherwise injure the lower lands and these are, therefore, DRAINAGE DISTRICTS 271 benefited although no drains are constructed upon them nor a drainage outlet given them. Lands thus bene- fited may be assessed for a proportionate part of the cost of drains, for the same reason that lands are assessed for the cost of levees which protect them from overflow. Conclusion. The several methods of assessing bene- fits and apportioning the cost of drainage works where cooperation of property owners is required in construct- ing and maintaining them have been carefully reviewed because no division of the work is more important. A failure to equitably distribute the cost has led to untold dissensions, litigation and delay in district proceedings. As the principles become better understood and the methods of applying them more systematic and logical, the difficulties assume less perplexing proportions. It is urged that those who are charged with the duty of making assessments examine all of the methods care- fully, that the leading and controlling elements which have a bearing upon the subject become thoroughly understood and appreciated. They should also be familiar with court decisions upon what constitute assessable benefits, and know of any limits placed upon special assessments by local laws. As a final word upon this subject, it may be said that in no part of drainage work is there demanded more conscientious service on the part of engineers and assess- ment commissioners. The consequences of careless or ill-considered findings are so serious to property owners, and often, incidentally, to the progress of a meritorious and needed reclamation project, that too great care cannot be exercised. Assessments of Railroads. It is apparent that the drainage tax upon railroads cannot be levied on the same basis as that upon farm lands. The usual method is to assess them a lump sum which by law must be propor- ^^2 ENGINEERING FOR LAND DRAINAGE tioned to the direct benefits received. To arrive at a conclusion as to what shall constitute a just amount, three things should be considered : the number of miles of railroad benefited, the amount of benefit received, and the total cost of the drainage improvement. The number of miles benefited may not include the total length of the road in the district, as not all of it may be through wet land. Among the direct benefits which should be counted, the following have been sustained by the courts: increased solidity of the roadbed; less danger of its settling because of boggy soil foundation; less liability of damage to the track from freezing and thawing of roadbed; fewer culverts and long trestles to maintain; decrease in cost of maintenance of roadbed; greater stability of fences and poles; and greater freedom from aquatic rodents that do much damage to a roadbed when water stands beside it. The cost of the improvement should be taken into account for the reason that the size of all other assess- ments in the district is governed by it, since they are a certain percent of it. Many railroad companies appreciate the value of drainage to their lines and to the territory from which they draw their traffic, and are ready to bear the share of cost justly apportioned to them, even going so far, in some instances, as to take the initiati\-e in promoting such improvements. Inter-urban lines are subject to assessments deter- mined in the same manner as those for railroads. . Tele- phone lines across country are benefited by drainage in convenience and ease of maintenance of the line, and in increased stability of poles. Assessments of Public Highways. The actual better- ment of the highway which is accomplished by the DRAINAGE DISTRICTS 273 drainage system of the district is the basis upon which public roads should be assessed. The construction of main drainage courses through a wet or swampy portion of the district crossed by a road renders all necessary embankments more stable and enduring, reduces the expense of maintenance due to settling and flattening of the banks, and eliminates many small culverts and long trestles formerly required for the passage of water, by the construction of one substantial bridge over the main channel. It removes standing water from the right of way and permits the shaping of the latter so that it can be easily mowed and thus kept free from noxious weeds. By the improvement of bad portions of the roads the entire system is made uniform in excellence and a sub- stantial and lasting benefit is conferred upon the com- munity at large. In this sense the improvement of a small part of a road benefits the whole as a highway, and all who travel over it. For that reason the assessment may be placed at a comparatively high figure, particu- larly since it is paid by all property owners of the town- ship or county upon its assessed valuation, in common with other taxes. As in the case of railroads it should bear a ratio to the cost of the work. For this reason an equitable method is to assess the highway a certain percent of the entire cost of the work based upon the length of road benefited and the degree of benefit. This should be deducted as a lump sum from the whole amount before the assessment is distributed over the farm lands, the percent being shown on the assessment sheet. Assessments of Town Lots. Town lots cannot be assessed on the same basis as farm lands. If there are only a few included in the district they may each be assessed a lump sum according to their relative size and 274 ENGINEERING FOR LAND DRAINAGE the degree of benefit, always remembering that the total cost of the drainage works should be taken into account as in railroads and highways. If a town, or any considerable portion of one, is included in a drainage district a method of classification of the lots should be adopted to meet the conditions. Usually a flat rate for a certain size of lot is adopted and all lots are assessed on that basis, if the benefit is practically the same. Some- times the value of the lot should affect the amount of assessment. CHAPTER XVII LEVEE DRAINAGE SYSTEMS Among the large projects which drainage engineers are being called upon with increasing frequency to ex- amine and develop are those requiring the construction of levees either to protect interior lands from overflow of streams, or coast lands from the encroachments of the sea. Protection and Drainage of River Bottom-Land. The topography of river bottom-land is such that a levee dis- trict along a stream is comparatively narrow, but may extend miles in length. Its width will be the distance between the stream and the nearest bluffs or high lands running parallel with it on one side, while its length may be from one large tributary of the main stream to the next, entering on the same side. Whatever its dimen- sions, the lever must so supplement the bordering high land as to thoroughly protect the enclosed area from overflow. Usually this will require its construction on three sides of the district, that is, along the stream and across each end, from the river to the bluff. But this, protection from outside waters serves as well to prevent the escape of surplus water from the land by natural channels, and hence provision for the interior drainage of the area is necessary. This must be so planned as to care not only for the direct rainfall upon the tract, but also in some cases for the water flowing from the adjacent high lands which may discharge upon it. Under some conditions seepage water percolating under the levee from the river must also be guarded agaihst. 275 276 ENGINEERING FOR LAND DRAINAGE The long stretch of levee required, in proportion to the area protected, the drainage system necessary, including sometimes a costly pumping plant, the continuous annual outlay for operating the pumps and maintaining the levees and ditches, all combine to make this method of reclamation more expensive than any other ordinarily used. For this reason, only land whose returns after reclamation will warrant so great expense should be thus treated. The successful engineer will bring to bear upon such undertakings his most careful consider- ation and utmost skill, A thorough study of the entire situation, as well as of other problems similar in charac- ter which have been successfully worked out elsewhere should precede the actual work upon the ground. Preliminary Survey. The preliminary survey for a levee district consists in running a series of level-lines across the proposed territory, as elsewhere described (See Survey of Valleys, Chap. V), thus locating ridges and depressions of surface ; in meandering streams or water- courses of any considerable size within its limits; and in taking sufficient levels upon the adjacent high lands to determine the boundaries of the watershed whose waters discharge upon the district. In addition to these data secured by instrument-work, the engineer must have all available records of the amount and distribution of the precipitation over the section of country under consider- ation, the high-water marks of the streams to be leveed, and estimates of the runoff for which outlet must be provided. The existence of any natural depressions or streams which may be utilized as drainage channels by means of sluice gates, should be'notcd. The Location of the Levee. As has been said, the protective levee ordinarily extends continuously around three sides of the district, but its exact location as to distance from the river in order to secure a solid founda- LEVEE DRAINAGE SYSTEMS 277 tion and to leave the right amount of floodway for the stream are questions of great importance to be settled by the engineer according to local conditions for which only general directions can be given. The volume of flood-water, its velocity, the nature of the soil composing the banks, the elevation, slope and stability of the ground in the vicinity of the levee are the factors which enter into a determination of its correct location. The general direction of the levee should be parallel to the stream, but this may be varied to take advantage of higher or more stable land, being particular to make the changes in direction by easy curves rather than sharp angles. The distance between the river side of the bor- row-ditch and the river's edge, or the width of the strip of land left undisturbed between the river and the bor- row-pit, will depend largely upon the nature of the banks, their stability and freedom from erosion, as also upon the volume of water for which a channel must be provided, but fifty feet is the minimum width that should be allowed. It often happens that the land along a river slopes quite sharply away from the bank, so that the levee must be built considerably higher when located at some distance from the stream than if placed near the bank. In such cases this con- sideration must enter into the decision of the location, as one affecting quite materially the expense as well as the stability .of the work. The closeness of the levee to the bank depends much upon the size of the stream and particularly upon the length of time that the water will stand against the levee. It should be located on stable ground where there is sufficient room for the necessary berm and borrow-pit on the river side, should avoid places which are exposed to erosion by currents and waves, and should cross sloughs and old channels by the shortest courses. 278 ENGINEERING FOR LAND DRAINAGE Dimensions. The height, width of crown and side slopes should each receive critical attention, as the safety of the levee depends upon them. Different levees vary in height from 4 feet to 20 feet, according to the height of flood to be provided for, while the same levee may run from 20 feet high at its highest part to o where the ends meet the high ground. The important point is to have the crown throughout its entire length at least 3 feet above the flood-plane of the stream, to guard against injury by possible higher floods or by wind waves should the levee adjoin open water. It will be found that the flood-plane takes the general slope of the valley, so that the crown should have a corresponding slope. This slope should be determined from high- water marks found at the time the survey is made. The return-levees, those extending from the river to the bluffs, should be carried back upon a level unless they follow a tributary stream which brings water from the bluffs, in which case their crown should be parallel to the flood-plane of the stream as in the main levee. If there are no flood records obtainable, or if a levee is to be built on the opposite side of the river also, then com- putations of volume of estimated flow during flood periods must be relied upon, and if data for these are meager or uncertain then a larger margin should be allowed for height of levee. A levee higher than neces- sary will be less costly than one too low, if there must be a discrepancy either way. The general height of levees is from 8 to 16 feet. The breadth and slope necessary to secure strength and durability depend in part upon the material of which a levee is built, as well as upon the method of construc- tion. A tough, gumbo soil is the most satisfactory mate- ri d. The minimum dimensions for one of this kind are a width on top of 6 feet, a slope on the river side LEVEE DRAINAGE SYSTEMS 279 of from 2 to I to 3 to I (preferably the latter), and on the land side of 2 to i, though 3 to i here is also better. If the material is sandy, or if the side of the levee is to be subjected to strong currents or wave action, flatter slopes must be used. A slope not steeper than 3 to i on both sides lessens the difficulty of keeping the levee in repair. Construction Survey. The survey consists of staking out the center line for the levee in the same manner as that for a ditch. Levels are taken at each station and a profile of the surface of the ground made, upon which is established the crown line of the levee, after which the fill at each station is computed. Slope-stakes should be set at each station to mark the location of the toe of the levee on each side. Frequent bench-marks should be placed at convenient points for the use of the en- gineer in making estimates of the amount of work from time to time, and for setting the final stakes on top by which the levee is to be finished. The method of sur- veying and of computing the cubic yards of fill are the same as that required for ditches. Construction. The first step in the construction of a levee is to remove all vegetation from the strip of land to be occupied by the embankment, including the grub- bing of stumps and roots to the depth of 3 feet, and the refilling with solid earth of the holes thus made. Fill all ditches crossing the embankment with solid earth up to the line established for the base of the levee. Such filling must extend not only under the foundation but across the berm, and for 10 to 20 feet on the land side of the embankment. Plow the surface of the site of the levee leaving a dead furrow in the center. If the levee is of firm and dense material, its height moderate, and exposure to the action of water occurs only at infrequent intervals, this plowing may be all that is necessary to 28o ENGINEERING FOR LAND DRAINAGE prepare the foundation. But if for any reason extra precaution is advisable, dig a continuous muck ditch under the center line of the levee. This should be from 3 to 4 feet deep, or even deeper, if there is danger from seepage at lower depths. It should be filled with a clayey mixture, well compacted and entirely free from all vegetable matter. This latter is an important point, and applies equally to all material used in the con- struction of the levee. A well-prepared foundation removes one of the most frequent causes of defective levees. Build up the embankment with scrapers, dipper- dredges or drag-bucket machines, each method having its advantages and its advocates. A more symmetrical levee can be made with scrapers. Those made with steam-dredges can be constructed more rapidly, and, if the earth is carefully distributed when deposited, are more compact and solid when completed than those made in any other way. An allowance should be made for shrinkage which takes place from the time the levee is finished until the earth assumes its permanent position. Where levees are made of dry earth by team labor in the ordinary way, 10% is allowed for this. When made with a steam- dredge much less shrinkage occurs. When earth is taken from the borrow-pit, where it is said to be "in place," and deposited in an embankment, it increases in volume about one-fifth part, after which it settles and occupies less space than it did before being dug. These facts should be remembered when the temporary and permanent grade for the crown are established. The number of cubic yards of fill paid for when the work is done by contract is the amount contained in the em- bankment as finally required. Borrow-Pit and Berm. With any method of con- LEVEE DRAINAGE SYSTEMS 28 1' struction the material must always be taken from the river side of the embankment, with a clean berm not less than lo feet wide between the inner edge of the borrow-pit and the toe of the slope. The borrow-pit must be shallow on the side toward the levee, its side slope never being steeper than the slope of the levee, that the latter may not be undermined. It should not be deeper than 3 feet at this side, with a bottom slope of 7 to I, and whatever width may be necessary to furnish sufficient earth for the embankment, but the greatest depth should in no case exceed 10 feet. Where there is danger from action of strong currents, it is well to prevent this when practicable by leaving 'bars or "traverses" of undisturbed ground, from 10 to 20 feet in width, nearly across the borrow-pit, at intervals of 250 to 300 feet, which will serve to check the current near the levee. Intercepting Drain. Where the water stands against the levee for some time, there is danger from seep-water which makes its appearance on the inner side of the levee. This is particularly true if the soil is a sandy, permeable loam. A six-inch tile-drain placed 4 feet deep and 8 feet inside the inner toe of the levee will serve to inter- cept much of this water as well as to make the base of the levee more firm. Such a drain must discharge into the drainage ditches at every practicable point, since but little grade can be given to it. Fig- 54 is a cross-section of a levee showing shape of embankment, borrow-ditch, etc., and location of tile- drain just mentioned. Maintenance. The engineer, upon completion of the levee, should leave careful directions with the land- owners as to its proper care and maintenance. A little constant watchfulness and necessary small repairs are better than yearly inspection, by which time extensive 282 ENGINEERING FOR LAND DRAINAGE r,:Q| "I :|o I s and costly repairs may be demanded. In times of flood I it is advisable to establish a patrol along the entire length of the levee. Protection of the slopes against the action of the currents and waves during flood periods is essential. A thick growth of small trees along the foreshore are an ex- cellent protection. Where there is no such natural growth, wil- lows, cottonwoods, etc., may be planted, but never nearer than 25 feet to the slope be- cause of danger from penetra- tion of the roots into the base of the levee. Another precau- tion essential to the preserva- tion of the slopes is the secur- ing as soon as possible of a good growth of tough sod over them, which is very effective in preventing erosion from rain storms or water action. No rank vegetation should be al- lowed, as it not only affords burrowing animals security from hunters, but the growth of bush roots, and growth and decay of weeds, loosens the soil and renders it more susceptible to erosion. A mowing-machine can easily be used on a 3 to i slope and possibly even on a 2 to I. Pasturing the levee is to O !z; O H u O u o LEVEE DRAINAGE SYSTEMS 283 an effectual way of keeping the vegetation cropped, but care is necessary to prevent damage by the tramping of the live stock. Burrowing animals are a constant menace to the integrity of levees, the muskrat being especially injurious because of his habit of beginning his burrow under the water surface and continuing it up and across the embankment a foot or two below the surface. A permanent protection for the slope on the river side, in the shape of a revetment of rock 6 to 10 inches in depth is sometimes constructed, but this is expensive and is required only in places partic- ularly exposed to running water or to waves. The use of the top of a levee as a wagon-road is not to be recommended. A road following the levee, if one is desired, should be on the level ground just inside of the toe of the inner slope, or on a banquet on the inner slope. A railroad on top of a properly constructed levee is not open to the objections that are held against a wagon-road, as there is no cutting into ruts or dis- placing of the crown. A railroad embankment should not, however, be made to form any part of a protective levee unless especially constructed for that purpose. Interior Drainage. The arrangement and size of the interior ditches merit the most careful consideration in levee districts for the reason that storage capacity is an essential factor in such drainage. If either pumping, or the periodic operation of sluices is relied upon, the ditches, and the soil also, must be capable of retaining a large volume of water and of delivering it constantly and uniformly to the pumps or to the sluices. To ac- complish this end the main ditches must be large and deep, 7 feet, if possible, and nearly level in grade, a fall of 3 inches per mile being sufficient. If open ditches are employed entirely, about one acre in twenty, or possibly in thirty, will be required for main and field 284 ENGINEERING FOR LAND DRAINAGE ditches. These ditches must be kept in such condi- tion that water will flow freely from every part of the system whenever its level is reduced by its escape through sluices or by the pumps. If the land is thoroughly tile- drained, the reservoir capacity of the soil is increased and a favorable condition for the economical drainage of the district is created. Where tile are liberally used, many small ditches that otherwise would be required can be omitted. Efficient drainage by pumps requires that the drains be designed to deliver the water slowly but continuously, and that they be kept in such perfect condition that they will deliver the water as fast as the pumps can remove it. If possible, all runoff from the adjoining hill country should be diverted and carried by gravity to the stream so that only direct rainfall and seepage need be removed by the pumps. Sluices. Outlets for the interior drainage of dis- tricts protected by levees where gravity drainage is possible may be provided by sluices extending through the levee and equipped with automatic gates which close when the water rises outside the levee and open when it recedes. Sluices may be depended upon in cases where the water of the stream rises quickly and recedes rapidly, the water preventing the discharge of the sluices for a few days only, not exceeding a week. Under such conditions the levees prevent the overflow of the land, during which time the interior ditches and the soil re- tain the water without injury until the stream recedes sufficiently to permit the discharge of the accumulated water. The thoroughness of such drainage is depend- ent upon the length of the storm periods and the amount of precipitation on the land protected and also upon the entire watershed of the stream. The data most essential to the engineer in determining the effi- ciency of the gate system are the number of days in sue- LEVEE DRAINAGE SYSTEMS i 285 cession during which the gates will be inoperative, and the frequency of such periods. If these exceed 5 days a pump should be established to assist the sluices. In designing the size of the sluice, the same coefficient should be used as would be employed for the gravity drainage of that section. The amount of head will, of course, depend upon the relative height of water inside and outside the levee. It will be safe, however, under ordinary conditions, to assume the velocity of the water through sluices to be 5 feet per second. In many cases the location will be such that the velocity will be much greater than this. The engineer should make careful computations of the capacity required, especially where no pumps are used. Unless the sluices are small enough to permit the use of iron pipes, concrete structures should be used. Sluice Gates. Each sluice should be furnished with an outward-swinging iron gate at the river end, and also a sliding hand-operated gate at the inner end. The latter is required in case the operation of the swing- ing gate is prevented by debris from the stream, which not infrequently occurs. It is also sometimes desirable to retain a part of the water in the fields during drought, which can be done by shutting down the inner gate. Both ends should be protected with strong concrete bulkheads, and cutoff walls should be placed around the pipe or concrete conduit at intervals of 20 feet through- out its length to prevent seepage along its exterior surface. The end bulkheads must be made with special care, the walls not less than three feet thick, and with founda- tions 4 feet below the bottom of the invert of the con- duit. The outlet end should be placed at low-water mark, if practicable, and the earth about the discharg- ing point should be paved with riprap. Diversion-Ditches. One of the serious problems con- 286 ENGINEERING FOR LAND DRAINAGE nected with the protection of lands which border hill or bluff lands is the control of hill water. Where it is gathered by natural streams that carry it direct to the river, it is necessary to construct what are called "re- turn levees" along such tributaries to prevent their AREA, 5180 ACRES Ditches 7 feet deep with level grade made by dredge Fig. 55.— Map of an Illinois Levee District. Bulletin 158, U. S. Department of Agriculture. flood-flow from spreading o\-cr the adjacent bottom land. It is also often necessary to improve the natural chan- nels of such streams so that silt which they carry from the hills will not be deposited before it reaches the river. Intercepting and dixersion-ditches are not in- frequently required at the foot of the slopes on the LEVEE DRAINAGE SYSTEMS 287 upper Side of the district to prevent an undue amount of water from reaching the protected land, for all drain- age that can be diverted and disposed of by gravity will lessen the first cost of the pumping plant, and the annual expense of operating it. Such diversion-ditches sometimes fill with silt from the hills and become useless, unless a receiving and settling basin is made at the foot of the slope. By taking advantage of the topog- raphy, a tract of 5 to 20 acres, or even larger, can be enclosed by a levee in such a manner as to receive the water from the hill stream where the bulk of the silt wjU be dropped and the water flow off through the out- let provided. This method of preventing injury to channels by silt is being successfully employed in some localities. The basins, of course, will in time be filled and become land of great fertility. Arrangements must then be made to use some other land near by for a basin. If proper care is exercised by the owners of the hill land, much of the discharge of water upon the low lands can be checked. (See Chap. XXI.) A map of a representative Levee and Drainage District is given in Fig. 55, showing the protection of river bottom-land. Besides the main levee, the return levees at each end, diversion-ditches and interior open-ditch system are indicated. Drainage by Pumps. Where the enclosed land is so far below the river or tide at their various stages that gravity drainage is impracticable, pumping plants must be installed to lift the water over the levee. In many localities land has become sufficiently valuable to warrant the expense, so that drainage by pumps is destined to become prominent in future reclamation work in this country. Location of the Pumping Station. The station should be located where the water of the district can be brought 288 ENGINEERING FOR LAND DRAINAGE to it most conveniently and where it can be most easily discharged. Usually the lower or down-stream end of the district is the most favorable point. Consideration should also be given to other features, such as security of foundation, accessibility of fuel supply, etc., for the plant is a permanent part of the drainage equipment which must be maintained for all time and operated during a part of each year. The plant should have: 1. A well-constructed gravity sluice with gates, such as have been previously described, should be built through the levee near the plant for the purpose of relieving the pumps of all water that can be discharged by gravity. The opening in the sluice should be low enough so that the highest point will be the level at which it is desired to maintain the water in the district. The entrance end of the pipe should be rounded to reduce entrance friction. The discharge end should have an automatic flap gate. 2. A suction bay deep enough to permit the suction end of the pipe to be covered when the water in the supply canal is at low stage. The ba>' should be pro- tected by a screen fence to prevent debris from being drawn into the pump. 3. A discharge bay which will allow the discharge end of the pipe to be submerged at the pumping stage of the district. 4. A pile foundation on which to erect the building and the machine which it is built to contain. 5. At some suitable point a comfortable dwelling should be built for the use of tlie manager of the plant. Ample provision should also be made for the storage of coal. Type of Prnnp. The centrifugal pump is the kind best adapted to drainage. It is simple in construction, LEVEE DRAINAGE SYSTEMS 289 takes but little space, and can be obtained in all sizes. The size is usually given as the diameter of the discharge pipe. Pumps are made with both vertical and hori- zontal shafts. The larger pumps are usually of the horizontal shaft type and those larger than 24 inches are made with double suction which has the advantage of balancing the side thrust on the impeller and shaft. In order to reduce the entrance friction and discharge velocity, the ends of the pipes are enlarged and made bell shaped. Steam is most commonly used for power, but gas or oil engines and electric motors are also successfully utilized. Where soft coal is abundant no more satisfac- tory or cheaper power than steam can be obtained. Electricity is more convenient, and where current can be obtained at a reasonable cost, small plants can be operated to advantage with that power. To Determine the Size of a Pump. The capacity of a pump is usually computed by assuming the water to have a velocity of 10 feet per second, as for example, the capacity of a pump with a 24-inch discharge (a 24-inch pump) would be the area 3.14 X 10 = 31.4 cu. ft. per sec; a 36-inch pump = 7.16 X 10 = 71 cu. ft. per sec. If we wish to drain a district of 5,000 acres, using a drainage coefiScient of yi inch, the volume to be removed per second would be 5000 X .021 = 105 cu. ft. per sec. A 30-irich pump would be rated at 49 cu. ft. per sec. and a 32-inch at 56 cu. ft. per sec, the two making 105 cu. ft. per sec, the required capacity. If a coefficient of X inch were used, one 56-inch pump would give the theoretical capacity. In all dis- tricts, however, not less than two pumps should be installed; both to be operated when the raaximum capacity is required", but only one when the minimum and ordinary drainage is needed- Since this type of 290 ENGINEERING FOR LAND DRAINAGE Fig. 56. — Plan Showing the Arrangement of the Parts of a Drainage Pumping Plant. LEVEE DRAINAGE SYSTEMS 29! pumps SO often fails to show, upon test, the rated capacity, they should be purchased under the guar- antee of the manufacturer, subject to a test after they are installed. Horsepower Required. To find the horsepower re- quired to operate a pump when the head and volume to be discharged are known, use the following formula: „ _ Lift in ft. X cu. ft. per sec. required X 62.5 XX. }r, = 550 Example. Required to remove 200 cu. ft. per sec. from a district with a maximum lift of 16 ft. What horsepower will be required? H P = 16 X 200 X 62.5 ^ 550 Since the efficiency of an engine is approximately 70 per cent of the theoretical rating the actual brake horsepower required would be .70 The capacity of pumps is usually expressed by manu- facturers in gallons per minute. To find the theoretical horsepower of a pump so rated we have „ „ Gallons per miiiute X head in feet X 8.33 3300 To this must be added a certain amount according to the effi^ciency of the plant. The essential parts of a plant and their arrangement are well illustrated in Figures 56* and 57* which show the plan and elevation of a fairly typical drainage pump- ing plant. Drainage Coefficient. The rate at which the pumps will be required to remove the water from the land will *From a professional paper by Prof. W. B. Gregory. 292 ENGINEERING FOR LAND DRAINAGE Fig. 57.— Elevaiiok Showing Essential Parts of a Drainage Pumping Plant. LEVEE DRAINAGE SYSTEMS 293 depend somewhat upon the size, arrangement, and grade of the interior ditches. If the arrangement and grade of the ditches are such as to lead the water to the pump rapidly the land near the outlet will be flooded unlesss- the pump has a large capacity. On the other hand, if the water is held back through lack of ditch capacity or by the bad condition of the channels, the land will remain wet notwithstanding the ample capacity of the plant. Ditches in a pumping district should be large to, afford storage and reservoir capacity to the end that the pump may be operated without frequent stops to permit the water to accumulate in sufficient quantity to supply the pump. In the upper Mississippi Valley a drainage coefficient of .25 to .3 inch is used in the design of plants though the tendency is to provide an auxiliary pump which will make the combined capacity about .5 inch, particularly where outside water passes through the district. It is found practicable on Louisiana cane plantations to remove as much as one inch in depth of water in twenty-four hours for a short time. In that section it is considered good design to make the ditches of the district with a capacity of .5 inch in depth over the land drained, and the pumping plants with maximum capacity of 1.25 inch in depth over the district in twenty- four hours. CHAPTER XVIII RECLAMATION OF TIDAL LANDS Many small areas of tidal marsh-lands within easy reach of large cities present attractive reclamation prop- ositions. The inherent fertility of their soil, their ex- emption from protracted droughts, the demand for all products that can be grown upon them and the in- creased healthfulness which their drainage will insure to people who reside in their vicinity, give an impor- tance to their reclamation which should not be over- looked. It cannot be denied that many attempts to reclaim tidal lands have failed at the outset or ulti- mately proved unprofitable. For this reason, the engineer should give the subject the most careful con- sideration from an agricultural as well as an engineering standpoint before undertaking reclamations of this class. The results of a thorough examination of the subject are contained in "Tidal Marshes and their Reclamation," Bulletin No. 240 of the U. S. Department of Agricul- ture, by Geo. M. Warren, drainage engineer, under the direction of the author of this book, from which the following discussion has been for the most part taken. Causes of Failure. Reclamation of this character is a form of levee districts in which the work is adapted to coastal lands and tidal conditions. From an ex- tended examination of such projects it appears that the following are the principal causes of failure: Lack of cooperation among landowners; Ignorance or disregard of the fact that many marshes RECLAMATION OF TIDAL LANDS 295 when drained will settle or shrink to such an extent that gravity drainage becomes insufficient and pump- ing must be resorted to; Levees of insufficient height, badly constructed, and poorly protected and maintained ; Sluices of insufficient size and of such poor mechanical construction that leakage back to the land greatly diminishes the amount of drainage that would other- wise be afforded ; Ditches so silted and choked with vegetation that adequate drainage of the land is impossible. Relation of Water-Table to Vegetation. Upon salt marshes proper, depending upon the height to which they have been built up, are found various sedges, joint- grass, salt grass, and black grass. On brackish marshes are found three-cornered sedge, snip-snap, cattails, cord-grass, wild oats and red fescue. On reclaimed' marshes where the ditch water rises to such a height as to frequently submerge and keep the lands saturated, reeds, cattails, and flags will flourish. Land which is occasionally submerged and but a few inches above the water-table produces the three-cornered sedge in great abundance. Little of value is obtained from land less than one foot above the water-table. At a slightly higher elevation, i to i>2 feet above the water-table, June grass and other native grasses come in, and with white clover or fescue afford excellent pasturage. If sluices and ditches can maintain the water-table within 6 inches above mean low-water outside, and this usually should be possible, it is safe to conclude that land situated ij4 to 2 feet above mean low tide would make good pasturage; 2 to 2^ feet above, good hay and corn- fields; and 4 to 4^ feet above, good wheat fields. Con- servative forecasts on the crop production of such lands under good management would be 2 tons of hay, 65 296 ENGINEERING FOR LAND DRAINAGE bushels of corn, and 20 to 25 bushels of wheat to the acre. The reclaimed marshes along the Delaware and New Jersey coast produce grasses on damp lands, and corn, timothy, rye, oats, buckwheat, potatoes, straw- berries, celery, melons, asparagus, and onions on the well-drained portions. Where fresh water is available and can be promptly removed, much of the saline matter can be washed out of the soil. The usual method of subduing a rank sod is by burning, and this is to be recommended despite criticisms which have been made. If the burning does not extend deeper than i 'foot, the ashes and charred matter improve the texture of the soil, correct its sour condition by chemical action and promote nitrification. Marshes with a deep soil which contains sufficient clay to render it somewhat slippery under foot when moist, are most likely to prove agriculturally profitable, and to be subject to only moderate settlement, as well as best adapted to the building and sustaining of levees, sluices and excavation of ditches. They are generally sour, and after draining, lime should be applied. Shrinkage of Marsh Soils. Marsh soils shrink when deprived of their water. Experience both in this country and abroad has shown that where marshes have been drained there is a long continued shrinkage of the land, the amount of which varies with the charac- ter of the soil, being more in those of a peaty nature and less in clay, silt and sand. Approximate sub- sidences noted in several reclamations are as follows: Green Harbor, Mass., 1872 to 1908, about 2 feet; Hackensack Meadows, N. J., 1869 to 1887, 3 to 3K feet; Cohansey Creek, Cumberland County, N. J., 2% to 3 feet; Salem, N. J., 3^ to 4^^ feet; Whittlesey, England, 7 feet in 18 years. Failure to discern the shrinkage in marsh soils has caused many to believe RECLAMATION OF TIDAL LANDS 297 that the tides rise higher than in former years, but there is no evidence that such is the case. Dikes. The general method of constructing dikes, or levees, has been described in the preceding chapter. Some additional suggestions should be noted since those required to protect the land under consideration must withstand the constant action of the waves and tides of the sea, instead of the waters of streams which over- flow their banks periodically, as is the case along rivers. They should usually be located upon the most stable land and, if possible, 100 feet or more from the shore. Where not well protected by a wide foreshore, the outer slope of the levee must be flatter than 3 to i, depend- ing, however, upon its exposure to the waves and the material of which it is built. Where waves come di- rectly against the levee, artificial protection is indis- pensable. This may be riprap or paving with large stones. It has been suggested that concrete blocks 3 feet square and 6 inches thick will form a durable revet- ment, and one cheaper than stone. Capacity of Ditches Required. There is probably very little tidal marsh in the United States so high or so favorably situated that successful gravity drainage will not ultimately call into requisition every artifice of the engineer in reducing the ditch water to the lowest possible level. It is necessary that storm water and seepage should be intercepted by the ditches and de- livered promptly to the sluice, and that there .should be adequate storage capacity to hold the undischarged drainage at times of excessive precipitation or inter- mittent sluice action by reason of continued high tides. To accomplish these ends there must be large storage facilities as near the sluice as possible, and the more distant lateral ditches should be designed as carriers rather than storage ditches. This arrangement places 298 ENGINEERING FOR LAND DRAINAGE the accumulated drainage where it is discharged quickly, the head necessary to move water to the sluice being reduced to a minimum and the discharge head of the sluice correspondingly increased. The small lateral ditches then become .real drains and continue their flow toward the reservoir or storage basin for a long time after the gates have closed. All ditches should be designed to reduce the friction head to a minimum. They should be on direct lines, free from obstructions and vegetation. The quotient arising from dividing the cross-sectional area of flow by the wet perimeter, or rubbed surface, should be as near a maximum as possible. This condition is geo- metrically complied with when the form is semicircular and the flow line on the diameter. However, in prac- tice, such form would be impracticable, and rectangular or trapezoidal sections are necessary. The most efificient width is twice the depth, but since velocities vary, not directly, but approximately as the square root of the depths, the efficiency is not materially lessened if the width is made three or four times the depth. From a consideration of numerous marshes and a study of rainfall statistics covering both the Atlantic and Pacific coasts, it would seem that ditches and sluices capable of caring for the runoff of a 3-inch rainfall in 24 hours over the entire drainage area would be ful- filling the conditions of an adequate yet not too costly design. With such a rainfall, actual measurements of runoff, which are confirmed by the known pore space of marsh soils, show that provision must be made for the removal of three-fourths of an inch per day over the entire area. This runoff amounts to 2,722 cubic feet per acre per day, but in \iew of the occasional failures of sluices to play, it is a reasonable and necessary assump- tion that storage should be pro\'idcd in the ditches for RECLAMATION OF TIDAL LANDS 299 all of this amount. It will also be assumed that the ditch water should not rise higher than i foot above mean low water, and that at the end of sluice play it will be lowered to within i inch of the outside water. On these premises the ditch area for each acre of land will be 3,000 square feet, or, in other words, about 7 per cent of the land must be given up to ditches. Under an average head of i inch, each square foot of sluice opening will discharge 1.5 second-feet. In one and one-half hours, the period of time a sluice would play, with the assumed height of ditch water and a tidal range of 7 feet, this will amount to 8,100 cubic feet, or 16,200 cubic feet per day. Since each acre yields 2,722 cubic feet per day, it is seen that each square foot of sluice opening would care for but 6 acres. This would lead to sluices of extraordinary size, and it is highly probable that if built, little advantage would be gained, for the reason that the high tides which usually accompany a storm make sluice action very uncertain, if indeed it be not entirely eliminated. Since the drain- age water is stored in the ditches, no harm can be done the land if two or three days, say five operations of the sluice, are required to discharge it, and therefore i square foot of sluice opening would protect 15 acres of land. The following table has been prepared along the lines above indicated. In view of the fact that slopes of >^ to i, or as usually dug by dredge, will in a silt-clay soil soon flatten below the flow line to about 2 to i, reducing the capacity and efficiency of the ditch, at is recommended that the bot- . tom, as excavated, be made about 9 feet wider than the tabular widths. It will generally be found preferable in large reclamations to use several small sluice-ways, placed side by side, rather than one large sluice opening. 300 ENGINEERING FOR LAND DRAINAGE H W H o H O ui SDtnis p UI 301 njg JO Siiiuado -i^^TD iID;ia uiBi^ }0 ■5^ -tJS UT aoinis JO i|d:^t0 tirep\[ jo UI aDinjs jo SujuadQ -IB3ID "3^ "I qD^TQ UIBJ/^ JO q;piA\ "ujo53oa ui 331 nts JO SuiuadQ -i'B310 HDlja UIEp^ JO UT 3D!n]s JO Siiiuado J^^ID "id "I n;piAV uio^:»og ui SDinis JO I *o«)*inio« ^•J^•oto (i wi^«) m moo M « rt «d- ^ in« r«.oo o m « ^f>o o ^oo « MMMMnnrtn Otoo t-«o n t-rooo ^oinM«ooo OiO m n oooo^ 4 H H n ■^o 00 Oi H (^ ^^o 00 M '^ ^. o >n M o*© in ao nln^•0(1■^oto^x In -^ MOO lOfi ao '^Moo iont-M« o ^o*o noo M tt) mo rooo «)Oi«mo^o ^t-M '^«) m moo M « M ro^^m« mo t^ o o t^ m ri d •-■Hr4nr*}(<)^-!»• Oi w)d mobod t^t^iNO m mam HMNnmm^n' mo fr-oo qi m ^o ot H H M H M M H 11 M m mo t*oo o»o m mmt^ao mo ■*» H HMMMMfitimmt*) M M m« ^^ ^-o^M N ito t-M ^«) H ^lOM ooe H IN m^w n\d o moimt^H dodo mm^moo MMMMMmm^m mo c-oo o n ^^ O\^•mao ^Ot^iio m moo tuay u\ paujua pu«l H N H H M n n (OWI RECLAMATION OF TIDAL LANDS 30I Construction of Sluices. Sluices should be built in the most substantial and workmanlike manner. In important works, and where suitable foundations can be secured, mass concrete has many advantages. Reen- forced concrete, because of its lightness and ability to withstand tensional and torsional strains, is especially to be recommended. If timber is used, it should be antiseptically treated, preferably with creosote (dead oil of coal tar). Wood impregnated with zinc chlorid, corrosive sublimate, or copper sulphate will prove less satisfactory on account of the solubility of these compounds in water. All hardware should be noncorrosive, preferably of bronze, brass, copper, or galvanized iron. The gate and its seat demand special attention. The link-hinge allows the gate to adjust itself to the seat, which should have a rubber or other resilient lining or cushion. To protect the gate and seat from the gnaw- ing of animals or meddling of passers-by, it is recom- mended that it be set within a chamber or large man- hole near the center line of the levee and both the outer and inner ends of the sluice be covered with suitable metallic bar screens. This position and protection of the gate would also insure its exemption from obstruc- tion and interference by floating debris and ice. To obviate cofferdam work, with the attendant ex- pense, when renewals or repairs on the gate are made, it is suggested that each end of the sluice be fitted with two or more permanent vertical grooves, or guides, go that stop planks may be tightly placed over the ends, and the imprisoned water inside the sluice pumped out through the chamber, or manhole, which should be sur- mounted with a suitable wooden or iron cover equipped with padlock. Not less than two "cut-ofT" lines of strong-tongued 302 ENGINEERING FOR LAND DRAINAGE and grooved sheet piling should be driven under the sluice and carried well into the levee on both sides to prevent seepage or "blow outs" under or along the sides. The weakest point in a levee is apt to be at the sluice, but if the sheet piling is driven deeply into the mud or to an impervious stratum, little apprehension need be felt. For the purpose of counterbalancing heavy gates that they may swing under slight pressure, several devices have been employed, but there is probably none in use which is not open to more or less objection. Com- plete submergence of the gates greatly lessens the need of any counterbalancing mechanism. Gates of the "barn door" or "canal lock" pattern have been exten- sively used abroad, and to some extent in this country. They are best adapted to tidal streams draining large areas and where it might be desirable to pass small boats. The closing of these gates by the rising tide is liable to be accompanied by so much shock as to damage the gate or fastenings. They are believed to be growing in disfavor in this country and unsuited to the conditions^ of our present comparati\"ely small reclamations. Since sluices are one of the most essential structures used in tidal land reclamation, it will be well for the en- gineer to become conversant with the following facts which have been learned by experience and are set forth in the bulletin quoted. A sluice will play longer for a giA'cn height of interior water the less the range of tide. The length of time a sluice will play is governed al- most exclusively by the behavior of the tide and by the relative elevations of the outer and inner waters. On the ebb-tide the gale will open when the water without passes the level of that within, and will remain open RECLAMATION OF TIDAL LANDS 3O3 until the succeeding flood tide rises to the level of the interior water. The coefficient of discharge of sluices having un- weighted wooden flap-gates in complete submergence is 0.64. Heavily weighted and poorly constructed gates may cause the coefHcient to drop as low as o.io or even less. Light gates with long radius of swing, good me- chanical construction and complete submergence are all favorable to a high coefficient of discharge. In the examination of a considerable number of gates in operation, sluice leakage was found to exist to an unexpected extent. The smallest measured was 23 percent, and the largest 97 percent of all the water discharged. The practice of making the sluices too small and setting them too high is general. The relative merits of the so-called "high sluice" and "low sluice" have been discussed wherever gates are used. The advantage is distinctly with the latter. Only in the case of an exceptionally high marsh and large tidal range should the top of the sluice be placed above ordinary low-water mark. The advantages of the low sluice are: It will discharge more water; Its life, if of wooden construction, is immeasurably increased by reason of being always submerged, and not exposed alternately to the action of air and water; Its effectiveness will not be diminished by any ordi- nary settlement or shrinkage of the marsh ; There is less liability of obstruction and clogging of the gates from floating sticks, reeds, and other debris, which on flood tide move toward the shore; It is less liable to injury or interference in its work- ings, by the action of ice. The advantages of the high sluice are that it is less 304 ENGINEERING FOR LAND DRAINAGE expensive to construct and more easily inspected and repaired. Illustrative Plan. Fig. 58 shows a fairly typical plan of a tidal drainage district on the west side of the Dela- FiG. 58, — ^TiDAL Marsh Reclamation. ware River which has been in cultivation for more than fifty years. The mean range of tide is 5.9 feet, the rise occupying 52.; hours and the fall 6^4 hours. The top of the levee is 9 to 11 feet above mean low water, but oc- RECLAMATION OF TIDAL LANDS 305 casionally has been overtopped. The tributary drain- age area is 488 acres, and 11.4 miles of open ditches, varying in width from 3 to 24 feet and in depth from 6 inches to 4 feet, accomplish the drainage, and occupy about 5.3 per cent of the surface of the marsh land. The area of the sluice opening is 12. i square feet or i square foot to 40 acres. This is insufficient to properly drain the land at times of heavy rainfall or adverse winds. The ditches are badly silted and choked so that their operation is too slow and storage capacity much reduced. The hydraulic gradient rises to 7 inches per mile, which is twice that required. The estimated cost of the levee, including the sluice, is about $6,900 per mile, and the reclamation of the marsh part alone has cost $54 per acre; based upon the whole drainage area, the cost is about $34 an acre. A fair return on the investment is being obtained. CHAPTER XIX DRAINAGE OF IRRIGATED LANDS The reclamation of arid land in the West, while con- tributing a large and valuable addition to our agricul- tural domain, has introduced a drainage problem of peculiar and significant interest to engineers and farm- ers in irrigated sections. Nearly every valley con- tains land that has been reclaimed at no little expense, which after being cultivated at a profit for a time has been abandoned or given up to crops of indifferent value because of its wet or alkalied condition. There are not less than a million acres of land in the States where irrigation is practiced which require drainage to make them profitably productive, and the constant increase in the acreage of irrigated land by government and private reclamation work is yearly adding lands which should be drained. Heretofore the tendency among farmers has been to wholly or partially abandon such lands and seek new fields, belie\'ing that the cost and difficulty of reclaiming did not, under the circum- stances, warrant the attempt. With increasing de- mand for land this is no longer the case, and as a result, drainage districts from 5,000 to 80,000 acres in extent are being organized for the purpose of constructing suitable drainage outlets. It is seen that the lands must be restored, and that draining must be practiced in irrigated as well as in humid lands. These condi- tions open up a field for the investigation and practice of the engineer which will widen with the extension of irrigation and become more important as agriculture 306 DRAINAGE OF IRRIGATED LANDS 307 in the irrigated States is further developed and per- fected. Before the reclamation of such tracts is under- taken, the engineer should become conversant with the conditions which produce wet lands in rainless regions and the theory and practice of successfully- draining them. Conditions which Produce Seepage. Water for irri- gation is obtained from some stream or reservoir and conducted by a canal along the upper side of a valley, and distributed by a system of lateral ditches to land which occupies a lower level. The canal and distribut- ing ditches often pass through porous earth and lose a considerable amount of the water which is turned into them, while in other cases the waste from this source is apparently small. The application of the water to fields is always attended with a greater or less waste because of difficulty in so controlling the dis- tribution as to supply the needs of crops without per- mitting a part of the water to escape into the subsoil. Where the soil is open this waste is sometimes one-half of the water applied, and where water is used with prodigality, a much greater amount finds its way into the subsoil. Some of this escapes later into streams or arroyos, but what remains as ground-water collects in the lower levels and after a time appears at the sur- face. This process goes on just as a basin or reservoir is filled from the bottom. No injury is manifest until the permanent water-table gets sufficiently near the surface to destroy crops either .by wetness or alkali, and to make the land swampy. The supply of water to such locations during the irrigating season is constant, and hence the process of saturation is continuous. If the supply of surplus water is quite liberal, a swamp is formed in which cattail flags and tules grow luxuriantly. Two structural characteristics of these soils modify 308 ENGINEERING FOR LAND DRAINAGE the behavior of irrigation water after it has been spread on the fields. The presence of sheets of hardpan which are of mineral composition, some Icinds dissolving slowly in water, and others not at all, deflect soil water from its course downward, causing it sometimes to take a lateral direction and shoot out upon a sloping surface in copious amounts. Where the soil is underlaid with gravel the surplus water from irrigation flows readily through it down the slope until arrested by a loam which has less permeability. Here saturation to an injurious extent takes place and water rises to the sur- face, due to the pressure exerted upon it by that occupy- ing a higher level. Arid soils usually contain liberal quantities of salts which are soluble in water and harmful to plants when concentrated at the surface, as when water passes away by evaporation. Frequently the poisonous effect of the salts is the first intimation the cultivator has that the land has become too wet. The injurious salts most frequently encountered are sodium chloride, calcium chloride, sodium sulphate, magnesium sulphate, and sodium carbonate, some one or two of these usually predominating in a given locality. Sometimes swamp- ing of the land occurs without injury from this source. While the foregoing are the essential features of the occurrence, cause and condition of seeped irrigated land, a great variety of soils and numberless peculiarities will introduce differing factors into each problem when the engineer essays to apply the remedy of drainage in dif- ferent localities. The general principles will be here discussed and local modifying influences must be con- sidered as they present themselves in practice. Preliminary Examination. It is first necessary to find the source of the water and where it enters the land which needs draining. Usually the wet condition of a DliAINAGE OF IRRIGATED LANDS 309 tract of land is not due to the water which is sup- pHed to it by irrigation, but to that whose source will be found at some distance up the slope. It represents the accumulation of seepage which has percolated through the subsoil from higher land. The topography of the surface indicates the direction from which the water comes, but not necessarily the path which it traverses. To determine this, a series of borings should be made with a two-inch auger, having a stem made of three- fourths inch gas-pipe in four-foot sections, which can be joined together by thimble couplings until a length of 12 feet is reached. A small steel rod is useful in sounding for gravel formations. By means of the auger, find the position of the water-table, and the depth to hard pan or to gravel, if they exist, beginning with the upper edge of the wet tract and sounding up the slope at intervals of lOO feet. It may also be well to dig some pits with a spade or post auger to ascertain the manner in which the water percolates through the soil. Eleva- tions should be taken with the level at the points where borings are made, the record showing the surface, hardpan or gravel, if they are found, and water level. The relation of surface to the water-plane, and modifying agencies in the soil will be shown. 'These should be plotted, the elevations recorded, and the point or line where the water attacks the field located. Fig. 59 is a map representing a survey of this kind, and showing the location of the drains which later were constructed and thoroughly drained the land. It will be observed that the depth to the shale was noted and recorded, and that the drains are located so as to inter- cept the water flowing from it. The depth of the ditches was about 6>^ ft., with gravel relief- wells under- neath them at numerous points. 310 ENGINEERING FOR LAND DRAINAGE In an examination, the depth of the source of water from the surface must be determined, for in one sense it is the key to the entire situation. All drains will be futile unless they in some manner reach the imme- diate source of the water and cut it off, both in volume and head. Examinations must be pursued until data sufficient to accomplish this have been secured. They should also cover the tract to be drained in such a way as to determine the character and depth of the saturated soil, and whether it contains hardpan, gravel, or other formations which will be factors in arranging the plan of drainage. The outlet for the drains need not be seriously considered until their necessary location has been ascertained, for it should be remembered that in- vestigations are first made on the upper side of the tract with the view of finding the depth and location of a drain which will head all the supply of water that feeds the field. The importance of ascertaining the source of the water in order to properly locate the drain cannot be too strongly emphasized. General Drainage Plans. Drains so located as to cut off the supply of seepage water are called inter- cepting drains, and with the accessories of small col- lecting wells to reach deeper supplies, and their con- nections with the main drain, form the Elkington system, previously described. (See Chaps, n and VI.) Since the location of such an intercepting drain must diepend upon the source and level of the seepage water, it may not be laid out in a straight line nor upon an even grade, the desideratum being the reaching of certain water points by it. As a rule, not many such drains are needed, if properly located, and as few as possible should be used. When the first drain fails to give the desired result it should be ascertained beyond doubt that it has been correctly located, before others DRAINAGE OF IRRIGATED LANDS 3" LEGEND Fig. sq. — Drains on Irrigated Tract in Colorado. 59 Herman R. Elliott, Eng., Montrose, Colo. 312 ENGINEERING FOR LAND DRAINAGE are laid in a further attempt to carry away the in- jurious water. On comparatively level or slightly sloping plains which require drainage, a few drains should be put in to prevent the accumulation of waste water due to irri- gation direct, because all drainage which the land for- merly had through the dry subsoil has been cut off. When large level tracts are to be treated, some attempt at uniformity of arrangement should be made, but the necessity of heading ofif the water by cross or inter- cepting drains should never be lost sight of. Little valleys, or draws, are sometimes found in a wet con- dition. Their slope and structure of soil is such that water has concentrated in them to the injury of that part of the field. A single drain will usually thor- oughly restore such tracts to their former condition. The alkali flats in a field will suggest that drains be run through them, if proper attention has been given to intercepting the supply of underground water from outside sources. Outlets. It is usually necessary to secure outlets by extending the drains to an arroyo, a "wash," or pos- sibly to the river, but not infrequently the water may be discharged into an irrigation lateral, where the drain- age water will serve to augment the irrigation suppl)'. Such water is not usually charged with enough alkali to be detrimental to the irrigation supply when min- gled with it. There are, however, irrigated areas comprising many thousand acres, requiring drainage, for which artificial outlet ditches must be made by cooperation of land- owners, who may invoke the aid of the State drainage laws for the purpose, as is done in the humid sections. The presence and operation of irrigation laterals make it necessary to carry irrigation water in flumes across DRAINAGE OF IRRIGATED LANDS 313 drainage ditches, thereby entailing some inconveniences which are pecuHar to arid regions. Covered drains for outlets are to be particularly recommended wherever it is possible to use them, but where large districts are organized and require a common outlet, a few large open ditches will be necessary and provision should be made for maintaining as well as for constructing them. Depth and Kind of Drains. Accumulation of soil alkali often accompanies seepage, and is due in a great Fig. 60. — Box Drains. measure to the high capillary power of irrigated soils which acts by bringing alkali-bearing water to the sur- face, where it passes off by evaporation, leaving the salt upon or near the surface. The height to which water will rise and evaporate in large quantities is the minimum depth allowable for ground-water level. Gen- erally a depth of 4 to 6 feet must be observed to satisfy these requirements, while depths of 6 to 8 feet are often needed to effectually intercept the underflow of seepage water. Covered drains should always be used for fields and 314 ENGINEERING FOR LAND DRAINAGE for outlets, also, up to the limit of cost which can be borne by the landowners. Hard-burned, round drain- tile are preferable to all other material, but wooden boxes may be used with success where it is impracticable to get the better material. They are made of such size as are required, the simplest being constructed of boards 8 inches wide and one inch thick, as shown in Fig. 6o. Such a drain is 6 x 8 inches on the inside. Where the ditch is in firm earth the bottom of the drain may be open, the sides being held in position by cross pieces as shown at a in the figure, but if the ditch is of a soft material the box should have a bottom with % in. lath blocks placed between it and the sides at intervals, leaving spaces to admit the water, as at b. They may be made in such lengths as will be convenient for laying. Cement pipe are used, but in some instances have disintegrated under the action of alkali, and in the light of present information upon the subject cannot be unreservedly recommended. Sewer-pipe with cemented joints should be used where the drain crosses an irri- gation lateral. Capacity of Drains Required. The supply of water is due to a constant seepage during the irrigating season, the amount fluctuating with the frequency of irriga- tion and the amount of water applied upon the land at any one time. If the subsoil of the land supplying the water is gravelly, the amouht is greater and reaches the drain more quickly than where the soil is more dense. Not uncommonly the irrigation canals leak and con- tribute an indeterminate quantity of water to the soil. An estimate of this amount can be made only after a somewhat extended examination of the land during the irrigating season by means of borings. These ex- aminations should cover the land lying between the DRAINAGE OF IRRIGATED LANDS 315 tract to be drained and the supply canals, for it is this land and not the area to be drained that should be con- sidered in this estimate. Some irrigators apply many times more water than others, resulting, as might be expected, in a corresponding larger volume of drainage water. The quantity can be estimated with some degree of certainty by establishing small test wells at various points in the wet area and making weekly meas- urements of the rise of the water in the wells. The amount that should be removed by drains will be the amount of daily rise less the solid matter and the capil- lary water in the soil of the area under consideration. For example, if the water rises one-half inch in 24 hours over the entire tract, and the pore space is assumed to be 50 per cent of the volume of the soil, one-half of this being occupied by capillary water and the other half by drainage water, the depth to be removed by drainage will be one-fourth or 25 per cent of the entire rise, equal in the assumed case to ys inch, or .0052 second-feet per acre or 3.36 second-feet per square mile. The volume may increase or decrease materially for the same area owing to a possible extension of the limits of the irrigated land from which the water comes, or to a change in methods of irrigating that land which will affect the amount of water that finds its way to the seeped tract. The amount of drainage water to be taken care of depends upon the acreage of the higher land from which the water comes, and not of that which needs drainage. The capacity required of the main intercepting drain may be roughly approximated by estimating the underflow of the contributing area at from lyi to $ second-feet per square mile, the former figure applying to moderately level plains of loam soil, and the latter to gravelly lands with considerable slope. Experience with these lands shows that the amount 3i6 ENGINEERING FOR LAND DRAINAGE of drainage is greater a year or two after the drains are installed. Construction. The construction of drains in some kinds of saturated land is attended with much difficulty and expense, while in others the work is as easily per- formed as in humid regions. The method of preparing the bottom of the ditch for either tile or box is the same as before de- scribed for underdrains. Where soft spots are encountered, no better method has been found than to lay the tile upon long boards placed in the bottom of the ditch. It is often necessary to sheath and brace the sides of the trench to some extent while it is being opened and the tile laid. Traction steam - trenching - ma - chines are successfully used where the land is firm, but fail to operate in many soils where drainage is needed. Where they can be used they lessen the cost and expedite the work. Gravel Covering. Much difficulty is experienced with sand entering the tile. The soil is frequently in a semi-liquid state, and during or soon after construction it is inclined to enter the joints of the drain, filling it more or less completely. Grass and weeds closely packed about the tile will frequently prevent this. Gravel, however, is much the best material for this purpose and should be obtained, if possible. When placed about the tile, as shown in Fig. 6i, it forms a permanent filter which admits water, but prevents silt from entering the drains. All filling above the gravel covering should be compacted as closely as possible. ■ Sand-Traps. These arc necessary in all but the most Fig. 6i. — Gravel Covering to Prevent Entrance of Silt. DRAINAGE OF IRRIGATED LANDS 317 compact soils, to collect the sand. (See Chap. XI.) They are also useful to admit water for occasional flushing of the drains when, on account of the light grades upon which they are laid, they become obstructed by silt. This is more apt to occur in irrigated land than elsewhere, because of the fineness of the particles of soil and the lack of cohesion among them in many localities where drain- age is required. For this reason the engineer will do well to introduce sand-traps frequently in order to facili- tate the maintenance as well as increase the efficiency of the drain. Relief-Wells. It is not al- ways possible to place drains deep enough to reach the supply of water that causes the saturation. Beds of water- bearing shale or of gravel which force water into the soil may be found eight or even twelve feet deep. Unless these supplies can be reached, drains will be of little service. The loca- tion of such strata should be found by the use of the steel sounding-rod and wells should be dug to the water-bearing formation. These should be boxed, or curbed, as shown in Fig. 62. and a tile inserted at con- venient depth to removethe water as it rises in the well, or it may be a pit made directly beneath the drain and filled with gravel, as shown in Fig. 63. Such devices tap the supply of water beneath, and by relieving the pressure, permit the water which is under static head Fig. 62 . — Twelve-foot Re- lief-well, WITH Tile-drain Outlet. 3i8 ENGINEERING FOR LAND DRAINAGE to rise in the well and flow away through a drain placed at a convenient depth. These methods are success- fully employed in draining soils underlaid with gravel, sandy loams and shale formations. In some instances a few wells placed outside the tract of wet land and dis- charging into a tile-drain will completely reclaim a large tract where any number of drains placed in the ordinary way would give no relief. Removing Alkali. The re- sults which follow the sat- uration of land are often serious by reason of the accumulation of injurious alkali, and these do not al- ways disappear readily after drainage has been accom- plished. While alkali is soluble in water and may be removed from the land by taking advantage of that property, the process is slow, requiring frequent irrigations, together with cultivation and continuous care. Co- pious flooding to dissolve the surface alkali and good drainage to remove the water that contains it, followed by cropping and continuous culti%ation, are the means needed to complete the reclamation. This treatment distributes a part of the alkali through the soil as the water passes through, and removes a part with the drainage water. Surface drains often facilitate the work by quickly remo\'ing water heavily charged with alkali. Timely drainage of irrigated lands will prevent all serious injury by alkali, but if neglected until salts Fig. 63. — Gravel Relief- well UNDER Tile-drain. DRAINAGE OF IRRIGATED LANDS 319 have accumulated in sufficient strength to completely destroy the crops, at least one season of continuous and careful treatment will be required to restore the soil to a productive state. It is a case where an ounce of pre- vention is worth many pounds of cure. Reclamation of Irrigated Land by Dredged Open Ditches. An example of the drainage of a large area of water-logged and alkalied irrigated land by properly located and constructed dredged ditches is found in the Yakima Indian Reservation in the State of Washing- ton, a map of which is shown in Fig. 64. The land is a fine loam with a gravelly sub-soil which borings show to be from 5 feet to 8 feet below the surface. The effect of irrigation during a number of years was to water-log and render useless about 40,000 acres of land which during the first years of irrigation produced abundant and valuable crops. Later a part of the land became a veritable swamp. The Reservation being under the control of the Bureau of Indian Affairs, an appropriation was made by Congress in 1910 for draining the lands. Borings and other examinations were made and from the information thus obtained ditches were located and constructed, as shown on the plan in Fig. 64,* the ditches being com- pleted in 1912. For a clearer understanding of the work it should be explained that the plan involved the construction of a main canal from the river westerly, parallel in a general way to'Toppenish Creek for a distance of 20 miles. At 2-mile intervals lateral ditches were extended north for xyi, miles, at the end of which were head ditches that in the aggregate formed a continuous ditch with outlets into the cross laterals which in turn discharged into the main outlet canal. The upper ditch intercepts *By James Wm. Martin, engineer in charge. 320 ENGINEERING FOR LAND DRAINAGE Fig. 64. — Irrigation and Drainage Ditches on the Yakima Indian Reservation, State of Washington. DRAINAGE OF IRRIGATED LANDS 32 1 the seepage from the land north of it. The two east and west ditches, with the cross canals, form a block of ditches which intercept all of the seepage and surplus irrigation and carries it direct to the river. As a result of the work which was finished in 19 12, the land between the main ditch and the creek is com- pletely drained without additional ditches. Crops were grown on the land the year following the completion of the ditches without flooding for the removal of alkali, and the entire tract which had gradually deteriorated and had been finally ruined has been restored to its former productiveness by draining. At the completion of the ditches the discharge of water from the entire 40 miles of ditches through the main canal was 200 cu. ft. per sec. The fact should be noted, however, that the soil being underlaid with gravel made the effect of the drains more marked and rapid than would be the case were the subsoil a clay. It should be further observed that land with a gravel subsoil, though adjoining a creek, did not have sufificient natural drainage to prevent water- logging, and the ruin of the land by seepage and alkali. CHAPTER XX DRAINAGE OF PEAT AND MUCK LANDS There are several million acres of muck and peat lands in the United States, large bodies being found in Wisconsin, Minnesota, Maine and Florida, and small detached areas in various other parts of the country. They are distinguished from other soils by their loose structure and the large percent of organic matter which they contain. The difference between peat and muck consists principally in the degree of decomposition of the vegetable material composing them, and the amount of silt which may have found lodgment between their par- ticles. Their fertility characteristics as well as their drainage properties place them in a class by themselves, and one requiring special consideration and treatment. It has been pointed out in foregoing chapters that in- trinsic fertility should be first considered when drain- age for agricultural use is under contemplation, and that the two should be investigated in connection with each other. It is but natural that these lands should have received tardy attention because of their less favored condition when compared with other soils, but they are now very properly attracting notice in com- mon with wet lands of all kinds which are subject to reclamation by drainage. It should be noted with reference to their origin that peat soils may be classed as "moss" peats and "grass" peats or muck, and that the materials of which they are formed are found in almost every stage of decomposi- tion and density. To these differences and physical 322 DRAINAGE OF PEAT AND MUCK LANDS 323 peculiarities is probably due more conflicting experi- ences in draining such lands than those of any other class that can be named. Peat Lands of Europe. The drainage and manage- ment of peat lands have occupied the attention of farm- ers and engineers in England, Scotland, Germany, Sweden, and other European countries for at least a hundred years. While the origin and composition of moss-peat in these different localities vary widely, their general characteristics with respect to drainage are quite similar. In the first place they have, in many instances, not responded to the ordinary methods of draining, and when by special treatment they were made dry, it was found that their subsequent need of moisture content was of no little moment, and methods of irri- gation were of necessity devised. We learn from the experience of engineers with moss-lands in England and Sweden that they can be made too dry, in which state they are as valueless for production as when too wet. The remarkable yield of grasses reported from these drained lands after being irrigated show that their proper water content is a vital factor in their produc- tiveness. It is quite possible that the need of irriga- tion has been lost sight of in later investigations, but all who are capable of giving an opinion upon the sub- ject admit that these lands must first be well drained before they can be fitted for the production of valuable crops. It is also noted, in a study of these marshes in various countries, that they are as frequently found resting upon sand as upon clay, and that there appears to be no material difference in the structure of the two or in their value after reclamation. Those underlaid with clay are drained with more difficulty, since the water must be removed from the marsh by means of frequent 324 ENGINEERING FOR LAND DRAINAGE and deeply laid underdrains. The clay bottom aids in retaining needed moisture and, where it can be reached, forms an excellent material for mixing with the peat, supplying, in a measure, it is claimed, the potash in which these lands are deficient. Several million acres of peat, or "moor land," are found in Germany, where in recent years the Govern- ment has established stations for experimenting with their reclamation. The results show that they can be profitably reclaimed. As has been said, the first step in such reclamation is drainage. After preliminary open ditches have made the land somewhat firm, tile-drains, 65 feet apart and 40 inches deep, dry the land with sufficient thoroughness. In some localities stops are placed in the drains when the flow runs low, in such a manner as to hold the water-table within two feet of the surface; in others the supply of water from beneath is sufficient for all seasons. Peat and Muck Lands in the United States. Turning to the peat and muck lands of our own country, we may say with reference to their productiveness, that while they require special treatment and skilful fertilizing, many of them are capable of producing profitable crops of a special character, these depending much upon the quality of the muck and the climate of the section in which they are found. The drainage problem con- nected with them is of vital importance, and, it may be added, the conservation of moisture as well. Experi- ments conducted in Indiana and Illinois by the State Experiment Stations, relating principally to fertility questions, show that fertilizers, particularly potash, are needed, but it is concluded here as elsewhere that before any system of improvement can be successful the soils must be well drained. It is conceded that the treatment of muck lands DRAINAGE OF PEAT AND MUCK LANDS 325 upon a clay foundation is more simple, as far as fer- tility is concerned, from the fact that the clay subsoil when mixed with the muck has a marked effect on its productiveness. An- instance of this kind is cited, in which plowing the soil after drainage sufficiently deep to bring some of the clay subsoil to the surface, con- verted a comparatively barren soil into one which pro- duced 60 bushels of corn, to the acre. Clay is in some instances mixed with the muck soils of the fens of England by hand labor, with great advantage to the quality and quantity of the crop. A general review of the production of peat lands in- dicates that they are particularly adapted to growing grasses, onions, celery, cabbages, potatoes, and root crops generally, and that they are more subject to both early and late frosts than other lands. Drainage Coefficient. Experience in draining the lands under consideration seems to indicate that the maximum runoff to be provided for by main ditches should not be less than for loam soils in the same climate. When once dried out, they require much more water to fill them than any other cultivated lands, but when once filled, as they are during the rainy season, or when snow melts in the northern climates, the land requires as great ditch capacity as any other. Muck soils are easily injured by surplus water and require prompt drainage, though by reason of their porous nature fewer lateral drains are needed to lead the water to the main ditches. Sand Subsoil. The lands are usually quite level, necessitating ditches with grades of one or two feet per mile. The underlying sand greatly facilitates the drain- age so that open ditches are effective when the excava- tion is extended well into the sand. In northern Wis- consin, where the peat formation is often not more than 326 ENGINEERING FOR LAND DRAINAGE two or three feet deep, ditches which were formerly dug four and five feet deep are being increased to 7>^ feet, in order to give more efifective drainage to lands lying at some distance from them. Ditches of this, depth placed one mile apart supplemented by farm ditches give fairly satisfactory drainage for farm crops. With regard to the stability of side slopes of ditches, the top peat and underlying sand exhibit quite different characteristics, the former standing very well at a slope of >^ to I, while the latter assumes a slope of about 2 to I. It is found best to excavate the top part of the ditch with nearly vertical sides giving a flat slope and broad bottom to that part of the ditch excavated in the sand. In some areas where sand is found, for the most part at a depth of 3 or 4 feet, muck may be found as deep as the ditch is excavated. In such places the effect of the ditch laterally will be restricted to such a degree that lateral ditches must be inserted quite freely to secure uniform drainage. Clay or Muck Subsoil. Where clay subsoil prevails, lateral tile-drains are required at intervals of about ten rods, in addition to the main ditches. These should be laid not less than four feet deep, where in either clay or muck they will remain in alignment and be permanent, since the ground at that depth will be wet and below the horizon at which settling takes place. If placed at a shallow depth where shrinkage is going on constantly, they will not be permanent. Settling, or Shrinkage. This is a factor that must be taken into account throughout the reclamation and management of such land. The top turf is often burned off to a depth of one foot as a preliminary to subduing and cultivating the land. The remaining soil, when drained, begins at once to settle by reason DRAINAGE OF PEAT AND MUCK LANDS 327 of the withdrawal of water from the large pore spaces which are a characteristic of such lands, and the decay of the fibrous vegetable matter of which the peat is composed. Three years after draining many peat soils have shrunken to one-half their original thickness. This statement applies especially to the shallow for- mations lying upon sand. At least 33 per cent of depth above the plane of the drains should be estimated for settling. Another characteristic relating directly to the drain- age properties of all soils containing a large per cent of organic matter is this: that as the soils become older they become more compact and require addi- tional drains to keep them sufSciently dry. In view of this fact the primary lateral drains should be so ar- ranged that others can be added as the necessity for them appears. This progressive method of draining is economical and effective if the probable requirements are anticipated from the first. This method should not, however, be applied to the main ditches. They should be made complete, and of the required size when first excavated. Regulation of Water. While muck soils require efiScient and thorough drainage, they also dry out rapidly and possess some properties pertaining to capil- larity, retaining and giving up moisture to vegetation in a manner peculiar to themselves, and not yet well understood by scientists. The peculiar moisture changes through which these soils are continually passing cause variations in their agricultural value as well as an erratic behavior with reference to drainage. It may be safely said, however, that for some kinds of crops, devices for controlling the height of the soil water during dry seasons should be applied to lateral, and possibly in some instances to main ditches, in order to secure the 328 ENGINEERING FOR LAND DRAINAGE best results from the land. For general field crops, a method of compacting the soil by pulverizing it finely and rolling with heavy field roller has been found to greatly assist in retaining the moisture during the dry part of the season. CHAPTER XXI CONTROL OF HILL WATERS The need of conservation and control of rainfall as well as of removal of surplus water, has been em- phasized in preceding pages. This is especially impor- tant upon agricultural lands with rolling surface or steep slopes. When unchecked by any device of the cultivator the rainfall in such localities is not only carried off the land before the soil can absorb enough to meet the needs of vegetation, but the flow of water is so rapid that it does great injury in its downward course. The cultivation of hill lands, especially when this is shallow, as is too often the case, leaves the surface in condition to be quickly saturated and moved down the slope. Small lengthwise depressions serve to concen- trate the water into rivulets which rapidly increase in size, and extend their eroding and devastating effects with every successive storm. The water with its volume of soil in suspension passes swiftly toward the main drainage stream, leaving some of its load of earth on the bottom-lands as it passes over them, and deposits the remainder in the channel of the stream when the velocity of the latter is not sufficient to carry it along. The result is the almost irreparable injury to the hill lands and the raising of the beds of streams so that they periodically overflow and render the valuable level land along their course useless. This train of calamities, involv- ing the depletion of cultivated hill lands and the ruin of the valleys for profitable farming purposes is recognized by all who are familiar with such situations, yet, as a 329 33° ENGINEERING FOR LAND DRAINAGE rule, only meager and ill-directed means are employed to obviate or mitigate these disastrous effects. The finding of an adequate remedy for these unprofit- able conditions merits the careful attention of the drainage engineer, even though it consists as largely in proper treatment and cultivation of the land continu- ously as in methods of drainage, but the latter play an important part in many localities. Drainage by Proper Plowing. One of the fundamen- tal principles of drainage should be recognized in the effort to control hillside waters, though the method of accomplishing it may not be commonly considered drainage. The principle referred lO is that surplus water should be removed, as far as possible, through the soil instead of over it. Natural drainage on slopes tends to remove the water too quickly, not permitting its proper absorption by the soil. If in the cultivation of hill lands the plowing consists of deep furrows across the slope and with the contour, both the flow of the water is checked and the soil is made receptive to such a de- gree and depth that a liberal part of each rainfall passes from six to twelve inches beneath the surface, where it either remains as moisture for the supply of growing crops, or distributes itself gradually through the soil, the surplus finally appearing at the foot of the slope as seepage, which may be taken care of by drains, as described later. Preventing Concentration of Water. It is readily seen that a method of cultivation should be adopted which will lessen the opportunities for the concentrating of the water and its formation into streams that sweep down the slope carrying soil and fertilizer with them. What is known as the level method of culture is adapted to this purpose, and should be used where heavy rains are liable to cut deep gullies in the slopes. Land CONTROL OF HILL WATERS 331 placed in grain or grass should first be evened on the surface in such a manner as to remove all existing gullies or so broaden them as to spread the water. This method prevents concentration of the water by facili- tating its passage into the soil and causing it to pass over the surface in sheets rather than in narrow streams. Such treatment of slopes is very important and in many kinds of lands will entirely prevent soil washing, with the added benefit of making the land more drought- resistant. Tile-Drains Needed. Where gullies persist in form- ing, despite all efforts to prevent them by proper treat- ment of the land, it will often be found that the erosion is caused by seepage at various points about midway between the crest and the base of the slope. Water which has run along a stratum of impervious subsoil oozes out upon the surface during the winter season to such an extent that spring rains quickly displace the softened soil at such points, and thus start a gully which concentrates the water and' which is rapidly enlarged to serious proportions. The efficiency of a tile-drain laid directly through and across seep spots at a depth of about three feet has been satisfactorily proven, and such a drain should be constructed of 4- inch tile, and extended to the nearest available point of discharge. If small stones are placed in the ditch for a depth of several inches over the tile, the good effect of the drain is often increased. Erosion may be arrested where gullies have formed, by properly preparing the bottom of each gully and laying tile-drains in them. Fill all the trenches and dress the surface by plowing until the gullies are leveled so that only broad, flat depressions remain. Surface- inlets of the gravel or stone pattern (See Chap. XI) should be put in near the upper end of such drains as receive 332 ENGINEERING FOR LAND DRAINAGE the accumulation of water from the upper part of the slope. These drains are especially valuable in meadows and pastures where the surface can be kept in sod, but may also prove of benefit in cultivated fields. Level land at the base of hills may be protected from the hill water when necessary by an intercepting drain of 6-inch tile laid parallel to the foot of the slope and along the line where the greatest seepage appears. But it is much better when possible to begin the interception at the top of the hill" by some or all of the naethods mentioned for the protection of hill- sides, and when this is done, often the drain at the bottom will be unnecessary. Level Terraces. The method of controlling the water by hillside ditches and terrace banks, once very common, is being superseded by the level terrace either cultivated or laid in grass, the object of this treatment being to distribute or spread the water over the surface instead of holding it back in concentrated form, as is the case in contour ditches and banks. The method usually followed in laying off and build- ing such terraces is to select a point about midway on the slope, and run the first line with the level, setting line stakes on a true contour, or on a light grade accord- ing to the plan adopted. Other terraces are then run in above and below this, spacing them 30 feet apart where the slope of the hill is steeper than 12 feet in 100 feet, and at a greater distance on the flatter slopes. After the line is marked, a wing plow drawn by four mules is employed in building tlie terrace. The first furrow is run on the lower side, throwing the earth up the hill on the line ; this is continued around the upper side throwing the earth down hill onto the line. One more furrow is run above and below and the terrace is com- plete. These terraces not only check the flow of water CONTROL OF HILL WATERS 333 and spread it out, but also collect and retain the finer soil and fertilizers washed from above, so that in a few- years the soil on and immediately above them becomes very rich. After the terrace banks have been allowed to stand about five years they are plowed up and new SECTION Fig. 65. — Level Terrace. ones constructed midway between the old ones. This style of terrace is illustrated in Fig. 65. The Mangum Terrace. It is probable that the form of terrace best adapted to the conservation of hillside water and soil is what is known as the " broad falling" or " Mangum " terrace. (Fig. 66.) As originated and constructed by Mr. P. H. Mangum on his farm near Wake Forest, N. C, it consists of a bank about 8 feet broad and 12 inches high, with a shallow ditch, or flat, 10 feet wide on the upper side, from which the material for the bank is secured. The terraces are constructed across the slope of the hillside with a fall of i inch per rod. In order to keep the terraces from becoming too long they are always run in the direction opposite to the 334 ENGINEERING FOR LAND DRAINAGE main drainage of the country. The vertical distance between them may vary, but is usually 3 to 3>^ feet. The crop rows are run with a greater fall than the ter- races and in the opposite direction, the amount of fall depending upon the slope of the ground. These are, therefore, at a small angle with the terraces, and are SECTION Fig. 66.— The Mangum Terrace. carried across them so that the entire field is cultivated. Outlets for the broad ditches are made at the most avail- able points. The theory of this terrace, which has proven true in years of practice, is that a broad shallow stream of water does not have as great velocity as a narrower and deeper one, and that by decreasing the velocity more water is taken up by the soil, and less soil and fertilizers CONTROL OF HILL WATERS 335 are washed away, or, in other words, concentration of water is prevented. This form of terrace is well adapted to all hillsides with the exception of those having slopes greater than 12 feet in 100. On these the banks would be too close to be economical, and the level terrace first described is the one to construct. Junction of Hill Watercourses with Main Streams. Perhaps no fact connected with the flow of water charged with silt is better demonstrated than that such water will deposit its sediment wherever the velocity is seri- ously checked. The deposit of beds of soil by hill water- courses at the foot of the slope emphasizes the need of so connecting such channels with the main stream that the sediment will be distributed and carried on. The best method of doing this will depend upon the local conditions of soil, amount of slope, and depth of ditch that can be obtained. The plan that should be first considered is to open a ditch with uniform grade and of sufficient capacity from the foot of the slope to the bottom of the main channel in the most direct course. If the main stream has been put in good condition this method will be the proper one to pursue. In some cases a better way may be to deflect the hill stream from its direct course to one down the valley, thus taking ad- vantage of its slope in securing a more uniform grade. CHAPTER XXII DRAINAGE OF HOME SURROUNDINGS Compared with the extensive drainage projects which may occupy much of an engineer's time, the drainage of farmsteads and village lots seems insignificant, and hardly worth consideration. This is unquestionably true if such work is viewed with reference to its difficulty or to the time it occupies, but when results are taken into account, the drainage of the home surroundings is of great importance, not only from a sanitary stand- point, but because of the convenience and comfort in- sured, not to mention the larger yield from garden and orchard and the added beauty of the grounds by reason of better lawns and more vigorous growth of trees, shrubs and flowers. The underdrainage of lawns and residence grounds should be governed by the same rules as that of land in general, care being taken to so locate the drains that they shall pass between trees and shrubs, as it is not desirable to have these directly over a tile-drain, as roots may enter and obstruct the drain. Gardens require more thorough drainage, laterals of 4-inch tile laid 3^ feet deep and 40 feet apart, being needed. Orchards are greatly benefited by underdrainage, and in those with clay soil or subsoil it is almost imperative. Not only is the yield increased but the quality of the fruit is superior where underdrains are employed. These should be of 4-inch tile, laid 4 feet deep between the rows of trees, connecting with a main at one side. 336 DRAINAGE OF HOME SURROUNDINGS 337 Cellar-Drains. A house should never be built on day soil without having a tile-drain laid before its foun- dation walls are erected, a few inches below them, and so protected that the weight of the wall will not rest upon it. It should be of 4-inch tile with a grade of 3 inches per 100 feet, and connected with a main hav- ing a free outlet. If the house is already built, or if for any reason it is preferable to lay the drain just outside the wall, it will be equally effective, but placed below the wall it requires but little extra trenching. The important point in either case is that it shall en- tirely surround the house and be below the level of the cellar floor, that it may intercept all outside water. If the house is on a side hill, there may be spring or seepage water that will need intercepting above the house, to protect both cellar and yard. In such a location, ex- aminations should be made to determine if this is the case. Roof-Water. Where the rainfall upon any building is not conducted into a cistern, it should be removed by drains. The eaves-troughs and down-spouts on the house should be ample, which they frequently are not, and the latter should connect with a tile-drain not less than 6 inches in diameter, and for large buildings 8 inches, laid on a grade of 3 inches per 100 feet, 4 feet from the wall of the building, and from 3 to 4 feet deep. At the points of discharge an upright pipe of sufficient size, set close to the wall and extending 8 inches above the ground, should receive the ends of the down-spouts and connect with the drain by a curved tile and a Y junction. Such drains may, if desired, form part of a farm system without necessitating any increase of its capacity, as the roof-water will pass away before that from the soil enters the drains. Stock- Yards. Underdrains in barn-yards and cattle- 338 ENGINEERING FOR LAND DRAINAGE pens laid without any accessories are of no value what- ever, because of the puddled condition of the surface, due to the tramping of the stock. Surface-inlets are an absolute necessity in such places. These must be fenced or otherwise protected. A shallow, open ditch encircling a stock-yard just outside its limits, so graded as to carry off the water from surrounding land, will aid materially in keeping such a yard dry. Special care should be taken to carry the roof-water of adjacent buildings away through underdrains so that none will be discharged upon the yards. This precaution is often neglected, and is responsible for much of the unsightly and annoying condition of farm-yards. Paddocks and pastures near the barn, particularly the parts that show their wet condition by a growth of inferior grasses, are profitably underdrained. Hillside erosion, which often occurs on rolling pasture lands, can be checked by placing drains in the gullies which have begun to form, and leveling the land over them. Intercepting drains along the foot of slopes will prevent too much wetness on the level area. Well-drained pas- tures are much more healthful for live-stock. Village Drains. The reclamation of large level areas and swamps by means of canals and a general drainage system will result in establishing new towns and ship- ping points, which will have a prominent part in the development of the region. A neglect to thoroughly drain the site of such towns will result in much dis- comfort and loss. The value of such drainage to towns has been proven in the level lands of Illinois where, in many localities, every street and cellar is provided with tile-drains. These towns are notably sanitary, as is shown by health statistics. Every town located in level sections should have a large tile outlet extending to the nearest drainage canal, DRAINAGE OF HOME SURROUNDINGS 339 and lines of 8-inch tile laid in every street 20 feet from the nearest property line and about i\}4 feet deep. This will serve to keep the street grade firm and to fur- nish an outlet for each cellar. These should be re- garded as strictly soil-water drains, and should in no case be used for house sewers. When placed on every street, all yards and gardens can be drained as may be found necessary, and there will be no excuse for the exist- ence of stagnant water, mosquitoes or malaria. Sur- face-inlets can be used to admit surface water at selected points. Silt-basins should be set at street corners and where branch drains enter. The town should have the engineer make a complete map and profile of every drain. A permanent bench-mark should be established to which all levels should be referred. In short, as much care should be taken in planning and recording the system as is exercised in developing and executing an expen- sive sewer-system. Road Drainage. Road making is a subject so closely allied to land drainage that it should be included in a drainage engineer's course of study. Much has been written on the subject, and the engineer may become fully instructed in the important art of making durable highways. These are coming to be more and more appreciated and demanded throughout the country. No attempt will be made to take up the subject here other than to mention the underdraining of roads to secure a firm road-bed. This is done by laying a tile- drain at the toe of the road embankment about 3 feet below the surface-ditch on one side of the road, or if through very boggy soil it may be advisable to have a drain on each side. This depth will bring it about 4 feet below the level of the ground and 5 feet below the crown of the road. If for the use of the road only, and not connected with other drains, 5-inch tile will be suffi- 34° ENGINEERING FOR LAND DRAINAGE ciently large. If forming part of a farm system its size must be determined as for other drains. Where laid along private farm roads, 4-inch tile will be large enough. Road culverts made of sewer pipe are often care- lessly constructed and covered with insufficient earth to be lasting improvements. The joints should be well cemented and the ends at each side of the road should be encased in concrete abutments two feet thick and extending two feet below the flow line, while the pipe should be covered to a depth of not less than eighteen inches. CHAPTER XXIII ESTIMATES AND ACCOUNTS The ability to make correct estimates is a valuable asset to any eng'neer. To calculate approximately the cost of an enterprise requires a comprehensive knowl- edge of the character and amount of work contemplated, and the probable cost conditions under which it will be done. A further demand is made upon the drainage engineer in that he is also called upon to appraise the value of the benefits which are anticipated as a result of the work. It may be urged that the individual, syn- dicate or board of commissioners who are responsible for the financing of the improvement are the ones upon whom this devolves. While this is true in part, the engineer will find that he will be called upon for advice based upon the relation of profit to costs, and his duties should include a critical study of benefits and profits in connection with costs. The engineer should not be a professional promoter, indulging in highly colored portrayals of the profits and advantages of the undertaking in hand, to the exclusion of all suggestion of unfavorable contingencies that may be met, nor should his representation of cost be smaller than well-considered facts will warrant. There is often a temptation to cheapen the plans to a point below profit- able efficiency, and to pass over cost items that will appear before the work is completed in order to make an attractive and impressive report. It is well for the engineer to exhibit an optimistic and resourceful tem- perament in dealing with such propositions, but it should 341 342 ENGINEERING FOR LAND DRAINAGE not blind him to the import of the facts which have a bearing upon them. Preliminary Estimates. Estimates are of two kinds, preliminary and specific. The former are made at the outset to determine the feasibility of the project and its probable cost and returns should the work be carried out. In general, it is a comprehensive statement re- garding the proposition as a whole in which the char- acter of the contemplated improvement is set forth, and its cost, benefits and results given within reason- able limits of accuracy before definite and detailed information obtained from surveys and computations has been secured. It is necessary to consider the work in the divisions into which it naturally falls, but the law of general averages obtains to such an extent that the totals become approximately correct. In making an estimate of the cost of a drainage sur- vey and plan for any area, be it large or small, the divi- , sions of the work which should receive separate con- sideration are: First, Cost of field surveys, in which the time that will be required to cover the area in the manner pre\aously decided upon must be estimated, including probable inclement weather (during which expenses will con- tinue without a corresponding amount of work being done), the salary of field engineers and rodmen, wages of axmen and helpers, and cost of subsistence and travel. Second, The time and force required for plotting the field records and making computations in the office, with corresponding salary charges. Third, Remuneration of engineer for professional ser- vice and superintendence, either upon a commission or salary basis, and a margin to cover unforeseen con- tingencies. A check estimate may be made by computing the cost ESTIMATES AND ACCOUNTS 343 by the acre or mile unit, based upon figures derived from former experience. In any event, tlie character of the land as to contour and nature of soil to be covered has such an important bearing upon the cost of the sur- vey that it should be critically examined by the engineer before he ventures a close estimate. For Owner's Benefit. Estimates of the entire cost of a reclamation project, such as a landowner or company who contemplate the drainage or betterment of land will need, include all the leading divisions of the work and their total. Estimates may sometimes be made by an experienced man at a cost per acre, based on a comparison of the area under consideration with others whose cost is known. The work may be considered under the following heads: Surveys, plans and specifications. Material and transportation. Contract price of construction. Superintendence and inspection. Subduing the land and preparing it for cropping. Interest on the amount expended until returns can be obtained. A common way of estimating the profits of such oper- ations is to place the market value of the land at the time the estimate is made against its market value after draining, and designate the difference as the profit. This method partakes of the speculative feature of business, and does not always represent a return based upon the production of the land. Probably the most rational basis for estimating the value of the improve- ment is that of rentals after the land has been reclaimed, the annual rentals representing the interest on the total investment, including first cost, or value, draining, and all other improvements. In the case of wet lands, draining is, of course, the improvement that will govern the amount of returns, but does not represent the en- 344 ENGINEERING FOR LAND DRAINAGE tire investment. The amount of rentals varies with seasons and price of products, so that an average return of a number of years should be taken instead of one giving either large or small returns. A most important consideration is the inherent value of the soil and the character and value of the crops it will produce. The cost of draining may be the same for lands differing greatly in amount and value of yield. This fact is often only partially appreciated by the casual observer. A failure to estimate the entire investment required before the land is brought to a healthful and profitable con- dition sometimes leads to erroneous deductions re- garding the financial merits of the proposition. The stability and permanence of the improvement is an important consideration and justifies the large first cost of lasting work which will yield a certain, though per- haps only a modest, annual return. The betterment of an estate by draining the wet lands within its boundary, thereby raising the entire area to a uniform standard of production and general excellence, is an operation which can be represented as exception- ally attractive to landowners because of the quick and substantial returns for the outlay. In many cases al- most the entire crop from reclaimed land may be placed to the credit of drainage, because the expense of oper- ating and managing the land, taxes, etc., were the same before as after draining. In other words, such better- ment virtually enlarges the estate or farm to the ex- tent of the land which has been drained. For Boards of Assessment. The preliminary esti- mates pertaining to a drainage district that are re- quired for the information of the authority desig- nated by the law to decide upon the merits of the project should include the following divisions of cost items: ESTIMATES AND ACCOUNTS 345 Preliminary proceedings and surveys. Location survey. Amount of damages to be paid. Construction called for by the petition. Bridges. Legal expense, engineering, superintendence, fees and con- tingencies. These items may be canvassed and estimated roughly, one by one, and the total cost approximated. The laws do not ask that these estimates be made public, but they are a necessary preliminary to ' comply with the requirement that before a petition for drainage is granted it shall be shown that the project will be con- ducive to the public welfare and that the benefits in general will be greater than the cost. A corresponding estimate of benefits may be taken up along the following lines: Character, area and value of the land included in the petition. Effect of the proposed work upon health conditions in the dis- trict. Addition to public revenues from increase of taxable property. Betterment of transportation facilities throughout the district. Benefit to farms by construction of outlets. Addition to farm profits and consequent appreciation of property. Opportunity for better social and educational privileges. In the attempt to assign a money value to these bene- fits, the temptation is to substitute general statements and platitudes for definite reasons, figures and argument. It is the judgment of the author that while definite financial benefits over and above the estimated cost of the work should be shown, in order to satisfy the re- quirements of the law, many others which have great weight may be appropriately named. The health benefits in some localities are most important, and are really sufficient to warrant the undertaking. An efifort 346 ENGINEERING FOR LAND DRAINAGE should be made to arrive at well considered conclusions upon that phase of the proposition. The betterment of roads and the encouragement of residents in the dis- trict to make permanent and sightly improvements, with a commendable regard for rural embellishment, should have weight, though their definite worth in money is not easily established. While the lands that are improved must be charged with the cost of draining, on the ground that they will pay the cost to the owners by increased production, the incidental advantages of such improvements will always appeal strongly to those who are contemplating sUch undertakings. Specific Estimates. These are made after definite quantities have been computed from data obtained by a survey. The price for which the several kinds and amounts of work can be performed must be estimated with reference to the conditions where the work is to be done. The engineer should view the work from the standpoint of the contractor taking into account the price of local labor and material. These vary so widely in different parts of the country, and the accessibility of the drainage area to towns and transportation facili- ties is such an important factor, particularly where small contracts are concerned, that no attempt will be made here to quote prices, but our efforts will be confined to classifying the different kinds of work and the units used in computing estimates. The practical advantage of planning the work so that specific methods of execution that have previously been proved successful can be applied, has been emphasized. If the work is thrown open to contract, those having the facilities for doing it according to the methods upon wliich the plans are based will be attracted and submit a bid. If the information which is furnished concerning the physical conditions that are of in- ESTIMATES AND ACCOUNTS 347 terest to the contractor is full and complete, a more in- telligent and closer bid can be expected. For Tile-Drains. After the total number of each size of tile has been computed and the length and depth of drains determined, the construction of the drains will fall under the following divisions: 1. Cost of tile in car lots at the factory. — In some cases the manufacturer will deliver tile, freight prepaid, at the railroad station nearest the work; in others the purchaser pays the freight. The former method is preferable. .The quality of the tile should be specified and the shipper should stand breakage. 2. Hauling from the factory or station. — The contract for hauling should include distributing the tile along the several lines, according to schedule, in piles of 25 each. This work is best done at a specified rate per ton of 2,000 pounds. The length of haul, and nearness to the public road of land to be drained, as well as its firmness and ability of bearing a loaded wagon, will vary the rate. The contractor should be responsible for breakage in hauling. 3. Digging ditches and laying tile. — This work is done either by the linear rod or by the loo-foot section at a specified price for a ditch of minimum depth (which for ordinary farm drains is three feet for tiles up to and including 6 inches), and an additional price per inch for greater depths. Larger tile and deeper ditches are contracted for in sections of 100 feet of the specific sizes of tile and depth required, and includes laying the tile to grade and securing them in place. This work is sometimes done with a machine at a price per 100 feet of completed drain. 4. Filling ditches. — This is done at a rate per 100 feet, the price depending upon the width and depth of the ditch, the stickiness of the earth and whether there are stumps which will interfere with team work. _ 348 ENGINEERING FOR LAND DRAINAGE 5. Engineering and superintendence. — This cost va- ries considerably, but usually runs from 6 to 10 per cent of the total. The engineering for work where small and comparatively inexpensive tile are used is as great as where large and expensive drains are constructed. If the cost data have been quite accurately secured, but a small contingent extra need be allowed. It is best, however, to add 5 per cent to the total estimated cost under this head. Open Ditch Systems. The unit in all considerations of earth excavation is the cubic yard. Computations of the amounts for ditches of different widths should be scheduled separately, as the price of excavation will depend in some degree upon the length of ditches of different widths as well as the total volume for the en- tire district. Ditches 30 to 40 feet wide and about 8 feet deep are more cheaply excavated per yard than either larger or smaller ditches, provided the contract is large. If the waste banks are to be spread for a road or shaped into a substantial levee, the cost will be greater than if the earth is deposited at random. If the excava- tion is to be made through a wooded territory, an esti- mate must be made for clearing the right of way, and for blasting large stumps. The accessibility of the proposed ditches for the delivery of the machinery is also a factor in the cost which must be considered by the engineer in estimating the cost of excavation. The following schedule of items should be estimated sepa- rately. Excavation ditches, classified according to width and length, with amount of excavation in each. Clearing right of way (if in timber), per acre or per linear mile. Bridges, size and kind. Legal expenses, regular and estimated litigation. Engineering and superintendence. Contingencies, commissioner's and clerk's fees. ESTIMATES AND ACCOUNTS 349 In submitting the estimates, the engineer should describe the measure of efficiency which riiay be ex- pected from the proposed ditches as fully as possible, for many drainage projects that are carried out under the law are but partial reclamations, and ditches must later be increased in number and size in order to furnish the complete drainage. Estimates of benefits should be made as suggested in a previous paragraph, substituting the totals in the specific estimate for those used in the preliminary or rough esti- mate. Accounts and Records. The engineer's professional training is frequently deficient in account-keeping, in making orderly and comprehensive statements of ex- penses and cost, and in classifying information which will be useful for reference. The engineer should be a business as well as a professional man, and arrange his accounts in such clear and concise form as to commend them to men who are versed in practical methods of business. Carelessness in this regard is inexcusable in an engineer, and if one finds himself deficient in this respect it will be well worth while to become conversant with business forms and methods, and exercise more than ordinary care in preparing formal statements, esti- mates, and expense accounts that are required in con- nection with the several lines of work he may undertake. Suggestions of forms of reporting drainage work are given in the Statutes relating to drainage, and in various books purporting to assist the inexperienced along this line, though in many cases these may be improved upon and adapted to special requirements. The engineer will find it to his interest to keep a card- index record of information upon drainage subjects, covering especially classified data on the cost of surveys which he has conducted or of which he has access to the 350 ENGINEERING FOR LAND DRAINAGE records, cost of construction under different conditions, examples of benefits of drainage, methods of assessments, cost of maintenance of work, and many other items which will at once suggest themselves when the mat- ter is taken under consideration. Such data become a valuable working capital which he can quickly refer to at any time, and rightly gives him a reputation for being well versed and experienced in his profession. Engineers' Charges. The character, magnitude and importance of the work, and the experience and reputa- tion of the engineer should control his remuneration, as they do in other branches of engineering. It is to be regretted that this is frequently not the case. Owing to the manner in which drainage work has developed, the fees commonly charged by land surveyors have been made the basis of those allowed the drainage engineer, while the drainage laws of some States go so far as to fix a lower fee for the surveyor when he acts as engineer in drainage districts than when he runs out property lines. It is obvious that the work of the drainage engineer and that of the surveyor is essentially different, and that the former should rank with that of other branches of engineering and command the rate of compensation given to others of its class. Many clients of drainage engineers recognize this and are willing to ignore the limitations set by law and allow a liberal fee propor- tionate to the importance of the work. Competition by some calling themselves drainage en- gineers, who offer to perform the field work at rates which engineers of training and experience cannot meet, often results in the work going to low bidders, whose services would not be accepted were the clients informed as to the comparative merits of the competitors. Trained and experienced reputable drainage engi- neers should adopt a scale of prices commensurate with ESTIMATES AND ACCOUNTS 351 their integrity and skill in laying out and directing the various classes of drainage work as those in other branches of engineering are doing. Two methods of making charges commend themselves and are adopted by such engineers. These are a per diem rate, and a percentage on the cost of the work. In either case the engineer's expenses are additional, and are paid by the client. For small projects or in con- sulting work, the per diem rate is, perhaps, the more common, and varies from $10 to $25 per day for the engineer in charge of field surveys, and from $50 to $100 per day for consulting work, depending always upon the importance and difificulty of the work and the reputation of the engineer. The percentage method is employed in large and costly undertakings which will extend over long time and be subject to delays. The amounts vary according to the nature of the service from i to 2 percent for pre- liminary survey and report, depending upon the diffi- culty of the work and the reputation of the engineer, to 8 to 12 percent for full professional service, supervision and management, depending upon the reputation of the engineer, the difificulty of the work, and inversely upon its cost, the greater the cost the less the percentage, as the amount of engineering work required is not, as a rule, increased in proportion to the increase in cost. This is especially true in tile-drain projects where the same amount of engineering is necessary for the small sizes of tile as for the larger ones. Underdrainage plans, however, require more field work than open ditch or levee systems. The percentages are computed on the entire cost of the completed work or upon the estimated cost pending completion, and are paid as the work progresses in such instalments as agreed upon. 352 ENGINEERING FOR LAND DRAINAGE A percentage basis may be adopted for one or more stages of the work, and a per diem or monthly charge for the remainder. And instead of one rate for the en- tire work, the various divisions may be charged different percents, as I percent for preliminary survey, 6 percent for construction survey, etc. Code of Ethics. In the execution and direction of all classes of work the honorable engineer will give his best efforts and skill to his clients, and be strictly honest with all who are in any way connected with the work, at the same time treating with courtesy and fairness all brother engineers. The following code of ethics, adopted by the Ameri- can Institute of Consulting Engineers, of New York, is a standard which should be recognized by all repu- table engineers: It shall be considered unprofessional and inconsistent with honorable and dignified bearing for any member of The American Institute of Consulting Engineers: (i) To act for his clients in professional matters otherwise than in a strictly fiduciary manner, or to accept any other remuneration than his direct charges for services rendered his clients, except as provided in Clause 4. (2) To accept any trade commissions, discounts, allowances, or any indirect profit or consideration in connection with any work which he is engaged to design or to superintend, or in connection with any professional business which may be entrusted to him. (3) To neglect informing his clients of any business connections, interests or circumstances which may be deemed as influencing his judgment or the quality of his services to his clients. (4) To receive, directly or indirectly, any royalty, gratuity or commission on any patented or protected article or process used in work upon which he is retained by his clients, unless and until re- ceipt of such royalty, gratuity or commission has been authorized in writing by his clients. (5) To offer coniniissions or otherwise improperly solicit pro- fessional work cither directly or by an agent. ESTIMATES AND ACCOUNTS 35 "^ (6) To attempt to injure falsely or maliciously, directly or in- directly, the professional reputation, prospects or business, of a fellow-engineer. (7) To accept employment by a client while the claim for com- pensation or damages, or both, of a fellow-engineer previously employed by the same client and whose employment has been terminated, remains unsatisfied, or until such claim has been re- ferred to arbitration, or issue has been joined at law, or unless the engineer previously employed has neglected to press his claim legally. (8) To attempt to supplant a fellow-engineer after definite steps have been taken towards his employment. (9) To compete with a fellow-engineer for employment on the basis of professional charges, by reducing his usual charges and attempting to underbid after being informed of the charges named by his competitor. (10) To accept any engagement to review the work of a fellow- engineer for the same client, except with the knowledge or consent of such engineer, or unless the connection of such engineer with the work has been terminated. INDEX Accessories to drains, 150 Accounts, keeping of, 349 AlkaU, in irrigated land, 308 removal of, 318 Angles, plotting of, 48 Application of formulas, 118 Appraisal of damages, 247 Arbitrary assessment of cost, 253 Arkansas, runoff investigations in, 185 Assessment of benefits, 249 by comparison, 259 by division into classes, 255 by percent of benefit, 260 importance of, 271 methods of, 252 of irrigated lands, 270 of public roads, 272 of railroads, 271 of town lots, 273 principles underlying, 250 Assessment of cost, ad valorem, 254 arbitrary, 253 flat rate, 254 Assessment sheets, District No. i, 256 District No. 2, 257 District No. 3, 262 District No. 4, 263 Azimuth, correction of, 39 Beardmore's formula, 96, 97 Bench-marks, 33 Bends in channels, 237 Benefits, assessment of, 249 of drainage, 63 percent of, 260 to highways, 273 to railroads, 272 Berm, for levees, 280 for open ditches, 206 Black Sluice District, 4 Blue-prints, 54 Boggy Bayou tract, 185 Bonds, 245, 253 Borrow-pits, 280 Bottom - land, protection of, 275 Bridges, across open ditches, 223 damages for, 248 Brush for cleaning drains, 157 c, values of, 164, 166 Camping outfits, 230 Caving of trenches, 155 Cellar drains, 337 Cement tile, 141 Central Park, drainage of, 16 Charges of engineers, 350 Chezy formula, 96, 97 Clam-shell dredge, 227 355 356 INDEX Classes for assessment, division of land into, 255 Clay tile, 133 tests of, 133, 136 (see also Tile) Cleaning tile-drains, 156 Code of ethics, 352 Coefficient, drainage, (see under Drainage) Coefficient for large pipes, 102 Comparison, method by, 259 Compass notes, how kept, 40 plotting of, 49, 51 Compass work, 35 Concrete tile, 141 Conservation of moisture, 62 Constant, a, 35 Construction, difficulties in, 153 of dikes, 297 of levees, 279 of open ditches, 201, 224 of underdrains, 143 specifications for, 157, 228 Construction figures, 87 Contour lines, 41 Contracts, 157 Control of hill waters, 329 Crooked channels, 237 Cross-sectioning, 208 Curvature of ditches, 232 Curved tile, 135 Curves, drainage, 197 Cutting off bends, 237 Damages, appraisal of, 247 for rislil of way, 247 Dams, efferl of, 241 Declination of the needle, 37 Denton, J. Bailey, 26 Depth, of open-ditches, 203 of underdrains, 78, 313 Designation of drains, 83 Development of drainage, i Difficulties in construction, 153, 316 Dikes, 297 Dimensions, of levee, 278 of small ditches, 207 Dipper-dredge, 226, 227 Distance between drains, 80 Ditches, (see Open ditches) Ditching machines, 20, 143, 144, 226, 316 Diversion ditches, 285 Double-main system, 77 Drag excavator, 227 Drainage, advance in methods of, 20 by plowing, 330 how accomplished, 57 laws, 245, 253, 255, 259 Drainage coefficient, 20, 23 a variable, 109 for dense soils, 116 how to select, 191 of levee districts, 291 of muck lands, 325 of underdrained soils, 108 relation to area, 190 relation to soil, 173 Drainage curves, 197 Drainage districts, 244 assumed. No. I, 255 No. 2, 258 No. 3, 261 INDEX 357 Drainage districts, assumed, No. 4, 248, 250, 267 Drainage engineers, 22 advisers of public boards, 24 notable European, 25 opportunities offered, 27 professional enthusiasm, 25 qualifications of, 22 Drainage Investigations, division of Dept. of Agri., v, 19, 175, 182, 184, 185, 187, 188, 192, 294, 30Q Drainage laws, 19, 23, 245, 253, 255. 259 Dredges, 21, 226 Dugdale, Sir William, 25 Elkington, Joseph, 26 system of drainage, 77, 310 Elliott's formula, for open ditches, 167 for underdrains, 103, 104, 106 Engineer's charges, 350 Engineering technique, 29 Equipment, camping, 230 field, 29 office, 45 Equivalents, table of, 127 Erosion, at curves, 234 of banks, 235 of hillsides, 329, 331 of levees, 252 Estimates, 54, 341 for Assessment Boards, 344 for open-ditch systems, 348 for owner's benefit, 343 for underdrain systems, 347 Estimates of cost for districts, 246 of tile, 127 preliminary, 342 specific, 346 Ethics, code of, 352 Evaporation, 172 Examples, (see Illustrative) Excavation, of open ditches, 210 of trenches, 145 tables, 213 Factors of benefit, 258, 261, 269 Father of tile-drainage, 16 Faure, 15, 100 Fens, the English, i, no FertiUty of soil, 252, 264, 265 Field-book, 32 Field equipment, 29 Flat rate, 254 Flood discharge, 192 Flow of water, formulas for, 94, 163 in open channels, 162 in pipes, 95 in underdrains, 93, 97 Formulas, acres drained, by ditches, 168 by underdrains, 107 Beardraore's, 96, 97 Chezy's, 96, 97, 163 discharge for, 97, 168 Elliott's, for open ditches, 168 for underdrains, 103, 104, 106 falling bodies, 94 Kutter's, 164 358 INDEX Fonnulas, Poncelet's, loi velocity, 94, 163 Weisbach's, 95 France, drainage in, 14 Frequency of drains, 80 Gardens, drainage of, 336 Government aid, 18 Government, U. S., aid, 18 Grade, for open ditches, 202 for underdrains, 85 limitations of, 125 Grading, 143 Gravel, for covering drains, 316 relief -wells, 317 Gravity, effect of, 60, 93 Gridiron system, 76 Grouping system, 77 Haarlem Lake, 7, 1 10 Hawkshaw, Sir John, 26 Herring-bone system, 76 Highways, public, assessment of, 272 benefited by drainage, 273 damages paid, 248 drainage of, 339 on ditch banks, 226 on levees, 283 Hillside erosion, 329, 331 338 Hill streams, junction of, 335 Hill water, control of, 329 Hoe for cleaning drains, 157 Home surroundings, 336 Hopson Bayou, 181 Hydraulic dredge, 227 Illinois, examinations in. III Illinois, rainfall in, 114 runoff investigations in, 188 niustrative examples, of computing excavation, 211 of computing size, 204 of use of formulas, 104, 118, 122 Inspection. of projects, preparatory, 66 of tile laid, 148 Intercepting drains, around cellars, 337 around stockyards, 337 at base of hills, 332, 338 for hillside homes, 337 in levee construction, 281 on irrigated land, 310 for seepage on hillsides, 331 Interior drainage, of levee districts, 283 of tidal marsh land, 297 Iowa, examinations in, III rainfall in, 115 Irrigated lands, alkali in, 308, 318 assessment of, 270 capacity of drains in, 314 depth of drains in, 313 drainage of, 306, 310 preliminary examination of, 308 seepage in, 307 Italy, drainage in, 14 John Johnston, 16 Junction of, hillstream and main, 335 shallow and deep ditches, 236 Junction tile, 134 INDEX 359 Klippart, J. H., i6 Kutter's formula, 164, 167 Ladder-dredge, 227 Large tile, 135 Lawns, drainage of, 336 Laws, drainage, 20, 23, 245, 253, 255. 259 Laying tile, 147, 316, 347 Levee drainage systems, 275 drainage coefficient for, 291 interior drainage of, 283 pumping plants for, 287 Levees, construction of, 279 dimensions of, 278 location of, 276 maintenance of, 281 waterway between, 239 Level, 30 Level-notes, leveling, 32 checking of, 34 illustrative, 33, 84 importance of, 32 Level-rod, 30, 31 Level terraces, 332 Location, of dikes, 297 of levees, 276 of open ditches, 201 of points, 48 of pumping stations, 287 of underdrains, 74, 81, 310 Louisiana, runoff investigations in, 175, 181 Maintenance of levee, 281 Mangum terrace, 333 Maps, copying, 52 Maps, farm drainage, 50, 90, 91, 268 irrigated land, 311 levee districts, 47, 49 marsh reclamation, 304 of drainage districts, 258, 259, 267 of underdrains, 88 preparation of, 46 titles of, 48, 49, 50 Marsh lands, reclamation of, 294 Memorandum, District 4, 269 Meridian, determining true, 38 Methods of assessing benefits, 252 Methods of drainage, advance in, 20 Mississippi, runoff investigations in, 181 Moor land, 324 Muck lands, drainage coefficient of, 325 drainage of, 323 in United States, 324 of Europe, 323 regulation of water in, 327 shrinkage of, 326 with clay subsoil, 326, 327 with sand subsoil, 325 n, value of, 164 Natural system, 76 New Orleans tract, rainfall in, 178, 179 runoff investigations in, 177 Non-folding rod, 31 Notes, compass, 40 cross-section, 210 36o INDEX Notes, level, 30, 84 plotting of compass, 49 Obstructions, in open channels, 237 in tile-drains, 156 Office equipment, 45 Open ditches, as drains, 58 bridges across, 223, 248 construction of, 201, 224 curvature of, 232 depth of, 203 erosion of banks of, 235 formulas for flow in, 163 location of, 201 obstructions in, 237 problems in work, 232 size of, 204, 207 velocity in, 162 Orange-peel ditcher, 227 Orchards, drainage of, 336 Outlet, completeness of, 252, 264, 265 natural, 250, 264 of tile systems, 73 on seeped land, 312 privileges, 252, 265 protection of, 148 raised, 241 Outlook for drainage, 18 Parkes, Josiah, 26 Pastures, drainage of, 338 Peat lands, (see Muck lands) Percent of benefit, 260 Plotting angles, 48 Plowing, drainage by, 330 Points, locating, 48 Poncelet's formula, loi ■ Porosity of tile, 139 Preliminary, estimate of tile, 127 inspection, 66 instrument work, 67 survey, 65 for farms, 68 for swamps, 70 for valleys, 69 records of, 7 1 Problems in open-ditch work, 232 Profiles, 52, 85 Pimips, drainage by, 287 horsepower required, 291 size of, 289 Quicksand, 154, 316 Railroads, assessments of, 271 benefits of drainage to, 272 bridges on, 249 damages paid, 248 on levees, 283 Rainfall records, Illinois, 114 Iowa, 115 Mississippi, 183 New Orleans, 178 Raised outlets, 241 Reclamation of tidal lands, 294 Reclamation of Yakima Indian Reservations, 319 Records, keeping of, 349 of preliminary survey, 71 INDEX 361 Records, tables of, Boggy Bayou, Ark., 187 clay tile tests, 137, 138 flood discharge, West and South, 192 Hopson Bayou, Miss., 182 Illinois, rainfall in, 114 tile outlets in, 112 Iowa, outlets in, 113 rainfall in, 115 Mississippi, rainfall in, 183 New Orleans tract, rainfall in, 178-179 runoff from, 177 Vermillion River, 111., 189 Willswood Plantation, La., 184, 185 Reduction table, 92 Relation of, depth and velocity, 170 soils to drainage, 62 Relief-ditches, 149 Relief-wells, 317 Rennie, Sir John, 26 Reports, in drainage districts, 245 outline for, 54 Results of drainage, 63 Right of way, 212, 247, 251 Roads, (see Highways) Roadway, on bank of ditch, 224 on levee, 283 Roof-water, 337 Runoff, conditions governing, 109 from large areas, 172 Runoff, from underdrained areas, 107 investigations, 175 Boggy Bayou, 185 Hopson Bayou, 181 in West and South, 191 New Orleans tract, 175 Vermillion River, 188 Willswood Plantation, 181 relation of to soil, 173 Sand-traps, 152, 316 Seeped land, (see Irrigated land) Selection of drain-tile, 133 Self-reading rod, 30 Sewer-pipe, specifications for, 136 used for drains, 135 Shrinkage, in drained marsh soils, 296 in drained muck land, 326 in levee building, 280 Side-slopes, 206 Sides of ditch, 225 Silt-basins, 152 Size of drains, 118 computing, 204 lateral, 124 limitations in, 125 Slide-rule, 46 Sluices and sluice-gates, in levee districts, 284 in marsh reclamation, 301 Small ditches, dimensions of, 207 Soil, effects 'of drainage on, 63 relation of to drainage, 62 relation of to runoff, 173 sources of water in, 61 -water, 57 362 INDEX South, the drainage in, 17 flood discharge in, 192 rundff investigations in, 175 Specifications, for open ditches, 228 for underdrains, 157 Stadia, points, location of, 40 rod, 31 work, 35 Staking out lines, for levees, 279 for open ditches, 201 for underdrains, 81 State drainage laws, (see Laws) Steam dredges, 21, 226 Stock-yards, drainage of, 337 Surface-inlets, 151, 338 Surface relief-ditches, 149 Survey, for contour lines, 41 for drainage districts, 245 for levees, 276, 279 for open ditches, 201 for underdrains, 81 preliminary, 65, 68 records of, 71 Systems of drains, 76 Tables, areas drained, 122 areas of tile, 129 coefficient c, 166, 167 curves and radii, 232 decimals of a foot, 89 discharge in second-feet, 120 excavation, 213 falling bodies, 94 fcut in decimals of a mile, 131 Tables, head in inches, 130 limit of size of tile, 126 mean and surface velocity, 170 right of way for ditches, 222 square roots of numbers, 128 standard sewer-pipe, 136 velocity, various depths, 170 Target-rod, 30, 31 Technique, engineering, 29 Telford, Thomas, 26 Terraces, level, 332 Mangum, 333 Tests of tile, 133, 136, 141 Thoroughness of drainage, 252, 264, 265 Tidal lands, reclamation of, 294 Tile, cement, or concrete, 141 clay, 133 cost of, 347 curved, 135 hauling, 347 introduced into U. S., 16 junction, 134 large, 135 laying, 147, 316, 347 porosity of, 139 preliminary estimate of, 127 selection of, 133 sizes of designated, 134 tabulation of, 125 tests of, 133, 136, 141 used in Europe, 115 vitrified, 134 Tile-drains, (see Underdrains) Topographic signs, 51 INDEX 363 Town lots, assessments of, 272 drainage for, 338 Traction ditchers, 143, 144, 227, 316 Transit, 29, 42 Trenching-machine, 143, 144, 316 TJnderdrainage, advantages of, 73 how accomphshed, 59 Underdrains, 73 accessories to, 150 cleaning, 156 construction of, 143, 316 contracts for, 157, 347 depth of, 78, 313 designation of, 83 difficulties in making, 153,316 formulas for flow in, 97 frequency of, 80 in hillside gullies, 331 inspection of, 148 kinds of, 133, 141, 313 location of, 74, 81, 310 maps of, 88 outlets of, 73 size of, 118, 124, 125, 314 specifications for, 157 velocity of flow in, 97 Value before and after, 255 Velocity, relation to depth, 170 Velocity formulas, for falling bodies, 94 for flow of water, in open channels, 163 in pipes, 95 in underdrains, 97 Vermuiden, Cornelius, 25 Village drains, 338 Vitrified tile, 134 Waring, Col. George E., 17 Water, -inlets, 223 soil-, 57 sources of, 61 -table, affected by drainage, 60 in marsh lands, 295 in seeped land, 307 Waterway between levees, 239 Weight of factors, 264 Weirs, effect of, 241 Weisbach's formula, 95 Wheeler, W. H., 26 Willswood Plantation, 181 y level, 30 Wiley Special Subject Catalogues For convenience a list of the Wiley Special Subject Catalogues, envelope size, has been printed. These are arranged in groups — each catalogue having a key symbol. (See special Subject List Below). To obtain any of these catalogues, send a postal using the key symbols of the Catalogues desired. 1 — ^Agriculture. Animal Husbandry. Dairying. Industrial Canning and Preserving. 2 — Architecture. Building. Masonry. 3 — Business Administration and Management. Law. Industrial Processes : Canning and Preserving; Oil and Gas Production; Paint; Printing; Sugar Manufacture; Textile. CHEMISTRY 4a General; Analytical, Qualitative and Quantitative; Inorganic; Organic. 4b Electro- and Physical; Food and Water; Industrial; Medical and Pharmaceutical; Sugar. CIVIL ENGINEERING 5a Unclassified and Structural Engineering. 5b Materials and Mechanics of Construction, including; Cement and Concrete; Excavation and Earthwork; Foundations; Masonry. 5c Railroads; Surveying. 5d Dams; Hydraulic Engineering; Pumping and Hydraulics; Irri- gation Engineering; River and Harbor Engineering; Water Supply. (Over) CIVIL ENGINEERING— Co««n«e