THE P R -A, T I C -A- E PRACTICAL LA N D DRAINER E Wrtatist Dn praiting XaOb. IX WItCH THN MOST APPROVED SYSTEMS OF DRAINAGE AND THE SCIENTIFIC PRINCIPLES ON WHICH THEY DEPEND, ARE EXPLAINED, AND THEIR COMPARATIVE MERITS DISCUSSED. VTH VULL- DIRECTIONS FOR CUTTINiG AND MAKING DRAINS, AND REMARKS UPON THE VARIOUS MATERIALS OF WHICH THEY MAY BE CONSTRUCTED. Xutmzrvuslg illuatratOb. B Y B. M U N N, LANDSCAPE GARDEXNE, NEW YORK: C. M. SAXTON, BARKER & CO., 25 PARK ROW. SAN FRANCISCO: H. IH. BANCROFT & CO. 1860. rid P4 Z, Ce toC eg:~~~ i:e v cok t r, ~ ~ ~ ~ ~' o cC' ~ ~ ~ ~ ~, A. m op ~~~~~~ i p h.~~~~~ o Sd o n~~~~~ c3 a UPON few subjects have opposite opinions been advanced with greater confidence, and adhered to with greater pertinacity by those who maintained them, than upon the question of the best method of draining land. Whilst this may appear extraordinary to those who have but little acquaintance with the subject, it is by no means so to those who have given due consideration to ts theoretical principles, and who have had some practical experience in draining. The causes of these great differences existing between men of unquestionable integrity, talent and experience, may be traced to the diversity of natural causes in operation which render drainage necessary; and in the-various methods which have been found by some to succeed, and by others to fail, in situations supposed to be similar, but in reality differing in geological formation, and in external relations. With the knowledge of these facts, the Author of the following pages has thought he would best serve 0 his readers by placing before them, in something of a 7 8 PREFACE. systematic form, the principal methods of draining that are considered most desirable; some for their permanent as well as efficient character, others for their less laborious and less costly nature. He has rather sought to explain various systems, and the mode of carrying them out, at the same time pointing out their comparative advantages, than to advance any pet system of his own. He has, consequently, availed himself largely of the labors of other authors of known experience and scientific attainments, and he does not, therefore, claim for himself any originality of principle or practice; yet he hopes that he has explained the principles upon which drainage should be conducted, and how they apply to the various systems for effecting it. And as regards the practical part of the subject, he trusts that the Farmer and the Horticulturist will find information in this volume, in a condensed and useful form, (which they must otherwise seek for in voluminous Agricultural works,) combined with observations arising from some experience in the subject of which it treats. Everybody knows that water runs down hill; but the Author begs permission to caution the reader against the assumption that, because he knows that, he therefore has nothing to learn as regards the preliminary knowledge which is requisite before he begins to drain his land. The.want of such knowledge is the too fertile cause of great loss of time, labor and money. PREFACE. 9 The Author, therefore, strongly, recommends the peru. sal of the few pages of the Introduction to those who have not paid attention to the subject which they discuss, before the practical operations of Land Drainage are attempted. Of the utility of Drainage it is needless in the present day to speak. But could Farmers and Landowners have the benefit of but a tenth part of the experience that has fallen to the lot of the Author, in the course of his professional duties in the improvement of land, he is certain that the extent to which Drainage would be carried would only be limited by the extent of each man's property. NEW YORK, March, 1855. NoTE.-The Author may be consulted professionally on the subject of Drainage, by addressing a note to him, Box 3292, Post Office, New York, or to the Publishers, No. 152 Fulton street, New York; 1* TABLE OF CONTENTS. INTRODUCTION. THE PHYSICAL LAWS ON WHICH THE DRAINAGE OF LAND DEFENDS.. 11 PART I. PRINCIPLES AND SYSTEMS OF DRAINAGE.................... 21 CHAPTER I. EXAMINATION OF LAND PRELIMINARY TO ITS DRAINAGE-DIFFERENT GEOLOGICAL FORMATIONS, AND THE INDICATIONS THEY PBRESENT.. 21 CHAPTER II. STATEMENT OF THE DIFFERENT SYSTEMS OF DRAINAGE, AND THEIR RELATIVE MODES OF OPERATION AND COMPARATIVE MERITS...... 30 CHAPTER III. DEEP DRAINAGE EPLALNED-ITS USE IN CUTTING OFF SPRINGS IN VARIOUS CONDITIONS OF WET LAND.........34......... (7D Vili CONTENTS. CHAPTER IV. FREQUENT OR THOROUGH DRAINAGE EXPLAINED —DIRECTION OF DRIAINS WITH REFERENCE TO LAND WITH SLOPIN'G AND LEVEL SURFACES-SKETCH OF FIELD OF DIVERSIFIED SLOPE WELL DRAINEDTHE FALL OF DRAINS IN RESPECT TO THEIR CONSTRUCTION-DEPTH AND SIZE OF DRAINS-DISTANCE APART AT WHICH TO CONSTRUCT THEM-REMARKS ON THE DISPUTE RELATIVE TO THE DEPTH AND DISTANCES OF DRAINS.................................... 48 CHAPTER V. SURFACE DRAINAGE EXPLAINED..................7........ 73 PART II. PRACTICAL DIREGTIONS FOR THE CONSTRUCTION OF DRAINAGE AND OBSERVATIONS ON THE TOOLS AND MATERIALS APPLICABLE TO THE PURPOSE..........................6.......................... 76 CHAPTER VI. LEVELLING.................................. 77 CaHAPTER VII. WIFFERENT KINDS OF DRAINS DESCRIBED....................... 82 CHAPTER VIII. MATERIALS ADAPTED TO THE CONSTRUCTION OF DRAINS...9..... 93 CHAPTER IX. THE MODE OF CUTTING DRAINS..................... 99 CONTENTS. ix CHAPTER X. BUILDING THE CONDUITS OR DUCTS FOR SECURING THE FREE PASSAGE OF WATER THROUGH THE DRAINS........................... 130 CHAPTER XI. FILLING UP THE CUTTINGS FOR THE DRAINS AFTER THE CONDUITS OR DUCTS ARE CONSTRUCTED......................... 142 CHAPTER XII. STOPPAGE OF DRAINS.................................... 155 CHAPTER XIII. SYPHON DRAINAGE —MR. J. B. DENTON ON THE SUBSURFACE LINE OF MOISTURE-COST OF DRAINAGE-MISCELLANEOUS MATTERS-TABLE FOR CALCULATING THE CAPACITY OF DRAINS AND DITCHES...... 167 INTRODUCTION. THE PHYSICAL LAWS ON WHICH THE DRAINAGE OF LAND DEPENDS. THE object sought by the drainagQ of land, being to remove water from it, it will be well to consider, 1st. The sources from which the water which we wish to drain away is derived; and 2d. The natural laws to which water when still, and when in motion, is subject. The operation of heat upon the waters of the ocean and of the land is continuously producing evaporation, by means of which large quantities of water are carried, in the shape of vapor, into the elevated parts of the atmosphere, and are there retained in an invisible form by the agency of electricity. When a change takes place in the electric equilibrium, clouds are formed from the water so raised, which, becoming subject to the laws of physical attraction, are thereby brought in contact with the mountains, and more elevated parts of the earth's surface. Giving out part of their heat, these clouds descend again upon the earth in the form of rain, fog, or snow, according to the temperature, and other meteorological conditions of the atmosphere. Once again upon the surface of the earth, the water becomes subject to its natural laws, and it sinks into the earth, runs down the hill-side, or lays upon the surface, 11 12 INTRODUCTION. as it may happen from the physical condition of the particular place on which it chances to fall. The water which sinks downward through the soil, and that which is carried through the interstices of rocks and mineral strata, obedient to the laws of gravity and capillary attraction, is distributed beneath the ground to a greater or less depth, until it meets with strata that it cannot penetrate; then it flows along such strata, or accumulates in large bodies, either in hollow basins or diffused through extensive tracts of the subsoil, until it finds vent upon the surface in the shape of springs; or, in other cases, by spreading over a large mass of soil it is held in suspension by it in the same manner as by a sponge. The land so saturated becomes unfit for the purposes of the husbandman. The natural laws by which water is governed are embraced by the two branches of science, called hydrostatics, which treats of water in a state of rest, and hydraulics, which treats of water when in motion. It is only requisite for tlhe present purpose to state shortly some of the laws of these sciences, without presenting, except so far as is necessary for explanation, the proofs by which the laws themselves are evidenced: FIRST.- Water and all fluids, both liquid and gaseous, when at rest, press equally in all directions. This results from the extreme minuteness of the particles. SECOND. — The pressure of a column of water upon its base depends upon its height and the area of the base; and not upon the thickness or width of the column. INTRODUCTION. 13 Suppose a and b, Fig. 1, to represent two vessels of equal height and capacity. The pressure upon the bottom of a -will be much less than that on the bottom of b. The pressure on a, at the bottom, F3e. 1. b a 4 b a c will be equal to a column of water represented by the dotted lines, but the pressure on b at the bottom will be equal to a column of water of the size of the whole base of b. The pressure of water in proportion to its height upon a level base is exemplified at c, Fig. 1. If a vessel of water be supposed to be divided into four, or any number of equal parts vertically, the pressure upon any part is represented by the sum of the aggregate addition of the parts above. Thus, if the divisions are one foot apart, the pressure at the first division will be equal to a column of water one foot high, at the second division to a column two feet high, and so on. THIRD.- Water at rest, and exposed on all parts of its surface to an equal atmiospheric pressure, always stands at a uniform level, whatever be its shape or magnitude. In Fig. 2, the size of the two parts of the vessel are very different; but if water is poured into either end, and the surface of the water is left exposed to the atmosphere, it will rise in both 14 INTRODUCTION. sides to the same level. It is this law (in connection with the law of gravity) that causes rivers to flow and water to. percolate through the earth. From this property of water arises one of the chief catuses of springs. It will be an evident consequence of the two first laws above stated, that if water be accumulated in mass within a FI. 9. mountain or hill-side, beneath the surface, and it finds egress by a narrow confined passage at a lower elevation, that the force with which it will issue from its lower orifice will be in proportion to the distance it has descended; in other words, in proportion to the pressure of the superincumbent vertical column of water above it; and thence arises the cause of the fountain jet. When, therefore, in draining, a spring is dug into, and the water spouts up with violence, the source of it must be sought for in higher ground, either near or distant. For, in some geological formations the water may travel far beneath the surface. FOURTH.-Capilary attraction. This may be termed a law of the science under consideration, although it is frequently regarded in connection with the general properties of Matter. And it merits attention from the two-fold reason of its apparent con ,NTRODUCTION. 15 tradiction of the last-mentioned law; and also from its being a very constant agent in the production of the evils that it is the object of drainage to counteract. Capillary attraction is that property of matter which enables water in small tubes or spaces to rise above its common level. The most simple example is the ascent of water in a sponge. Place a sponge on a glass of water with one end of it just touching the water, and the water will ascend. Take two plates of glass, place their flat sides near each other on one side, and touching each other on the other (Fig. 3), and then put their ends in water. The water will ascend between the plates and stand with a curved surface; the highest part being where the plates touch, as in the shaded line of the figure. FIG. & In the same way, as through a sponge, will water ascend, and be held in suspension by the soil, as is familiarly exemplified by the ascent of water in a flower-pot from the saucer beneath it. It will equally ascend into the pot whether the latter contains a plant or earth only. Capillary attraction, when drainage, whether natural or artificial, is efficient, becomes valuable 16 INTRODUCTION in its operation upon the growth of vegetation. But it produces results so vastly extensive and so continuous in their effect, that its importance as a cause of surplus water must not be lost sight of by the drainer when he is investigating the condition of land. Having stated the chief natural laws applicable to the subject, let us briefly refer to their mode of operation. Whilst upon the earth's surface, the motion of water is regulated by its weight or gravity as the operating force; and that is interfered with principally by the antagonistic force of capillary. attraction, by evaporation, and by the conformation of the substances over or through which it passes. Suppose rain to fall, or water to run down a hillside upon a flat surface below. If that surface be rock, impervious to water, it flows over the surface until it meets with a lower. level, by which it passes off; whether that be a fissure in the rock, (in which case it forms a cascade, and afterwards a river in the lower ground beyond,) or by a lower level of equal capacity with that from which it flowed, (in which event it would, as before, flow evenly over it.) But if the rain descend upon soil instead of upon rock, it will be carried by its weight downwards through the soil with greater or less velocity according to the greater or less porous texture of the ground on which it falls. As soon, however, as a portion of the water is beneath the surface, capillary attraction begins to exercise a certain amount of force in addition to the one of gravity, which continues its influence. This'attraction retains INTRODUCTION. 17 within the pores of the soil (and which may be viewed as an accumulation of minute tubes) a certain portion of the water, and the remainder only then passes down. wards by the force of gravity. It is found, moreover, that the power of capillary attraction varies in different substances; and it varies also in force, in a ratio inverse to the size of the tubes in which it takes place. Vegetable soils are favorable to the increase of the force in a greater degree than clay, in so far as regards their texture; but they part with water more readily. Whilst clay, from the more minute size of its pores, commands in that respect a greater force of capillary attraction than vegetable soil, and retains water with greater tenacity. Assume, then, sections to be made on the sides of two hills, one of sand and the other of clay, of equal height, and that rain fell on the top of each, the observer who placed himself at the section to watch the course of the descent of the falling shower through the soil, would find that the water upon each hill-top would sink down perpendicularly a certain distance, and would be attracted, or sucked up, by the topsoil; but if the quantity falling was greater than the rapidity of its downward course, (owing either to the close nature of the soil, or the intervention of rock or other impediment), the surface-soil becoming saturated, the water would be seen to ooze out and run down the face of the sections of each hill. So far, the phenomena presented would be identical. But the following difference in the two sections would be noticed: the perpendicular distance from the hill-tops, or surfacelevel, at which the water first oozed out, would be found to be much less in measurement in the side of the sand. 18 INTRODUCTION. hill, than in the qase of the clay-hill; and the reason is this: the superincumbent weight of water requisite to counterbalance the power of capillary attraction in the sandy soil, would be much less than that which was necessary to counterbalance the same power in the closegrained clay; and, consequently (by the natural laws above stated), the column of water above the oozing point would require to be much higher to effect the object. Inasmuch, however, as the force of capillary attraction does not prevent the passage of surplus water through the interstices, in substances upon which it is acting, whilst, on the one hand, it will always Iretain so much water as its power can command (and the extent of which will, as before mentioned, depend upon the nature of the substance, and the size of the tubes), it, on the other, presents no obstacle to the continued passage of water from the surface to the substrata: the veloc. ity with which it will so pass depending upon various additional considerations. It is upon the above data that the whole process of Under-draining is based. But we must now inquire what becomes of that part of the water which is not held in suspension near the surface by capillary attraction, when, by its gravity, it has accumulated in quantities in the substrata below. The passage downward continues in perpendicular lines from the surface, until its further progress in that direction is impeded (as has been before observed) by some non-porous obstacle, when, if it cannot find vent laterally, it accumulates, and, obeying the law of finding a level, it forms a "water-line" at a given depth (sometimes called a water-table), which level is elevated nearer to the surface, in proportion to the quantity fall. INTRODUCTION. 19 ing upon such surface. Thus it remains; stagnant, except soSfar as its mass is diminished by the capillary attraction* constantly going on in the soil above the water-line, which is induced to supply the loss of moisture in it, occasioned by the evaporation which is constantly emanating from the surface. In this condition it is that, for profitable farming, land, when this water-line is so near the surface as to * Professor Leslie calculates the rise of water in coarse sand or loam as follows: If the gravel were divided into spaces of a hundredth of an inch, the water would ascend 4. inches, and so on to a ten-thousandth part of an inch, when the height would be 25. feet. To make this calculation good, the pores should be continuous, and always open. In most soils, the cohesion of the particles, and consequently the diameter of the pores, is affected by the contact of water. In chalk this is not the case. To speak first of this substance: In chalk, the pores, which are not to be discovered by a strong microscope, are always open. A piece of dry chalk, six inches high, of which the foot is placed in contact with the surface of the water, absorbs about one-third of its bulk, and about one-fourth of its weight; it will become quite saturated in a short time, say one hour, so that it will take up no more, though immersed in water. Moreover, if suddenly immersed when dry, it will not be thoroughly saturated, a portion of the air contained in the pores being impounded in the centre. If a second piece be placed on that saturated, the water will pass through one to the other, and so on. About thirty pieces, piled on each other in a glass tube, the point of contact between some of them being not more than the surface of a pin's head, become saturated in about two months, so that the top piece, when immersed, would not take up more than the turn of the scale in addition. Hence, we see how water is lifted in chalk, which will not part with a single drop by drainage. Clay, when submitted to water, also becomes saturated by capillary attraction, but much less rapidly than chalk. —Gardener's Chronicle, 23d July 1853. 20 INTRODUCTION. interfere with vegetation, requires to be drained, no less than it does when the water stands on tle surface; and this introduces to us the question of the manner of effecting that object. PRINCIPLES AND SYSTEMS OF DRAINAGE. CHAPTER I. THE EXAMINATION OF LAND REQUIRING DRAINAGE. THE Art of Drainage may be defined to be, that preparation of land for the purpose of the husbandman which places it in a fit condition for retaining so much and no more moisture, and for subch periods of time, as is best adapted to the vegetation and growth of his crops. This, of course, includes the removal from the land of superabundant water, whether upon the surface or beneath it. No one will assume that it is practicable in all cases to attain perfection in this respect; but in this, as in all other human pursuits, he who would succeed must present the ideal at least of perfection to his mental vision, as the object to be aimed at; and then he must use the best means within control to attain as nearly to the image set before him as circumstances will permit; always, in his efforts, keeping in mind the fact that his personal energies to attain his object, being within his own control, must be lavished without stint. Much has been done in many matters with small means, but with such energy. It should be observed, moreover, that placing the soil in a fit condition as to the quantum of moisture for vegetation, is not the sole object of moment to the husbandman to be attained by draining. Another and (s3) 22 LAND REQUIRING DRAINAGE. very important consequence that results from it is, the elevation of the temperature of the soil immediately under the surface. This, during the greater part of the year, is of much importance to vegetation. The advantages of draining land are now so generally known, that it would be superfluous to do more than advert to them. Suffice it to say, that, whilst it renders much waste land valuable which was before useless, it renders doubly productive much land that already is valuable. In the report on draining, in the Transactions of the N. Y. State Agricultural Society, for 1848, the committee state, in reference to upland, " that there is not one farm out of every seventy-five in this State but needs draining-yes, much draining-to bring them into high cultivation; nay, we may venture to say, that every wheat-field would produce a larger and finer crop if properly drained." In order to simplify the subject, it is proposed to divide this volume into two parts. The FIRST PART will treat of the principles of Drainage, the various Systems in use, and their adaptation to different descriptions of land. The SECOND PART will contain practical directions for the construction of Drainage, and will also explain the materials that can be made available for the, purpose. The first object to be looked at in regard to draining, is the source and cause of the superabundant water in the land about to be drained. This must be sought for in cases where it is not self-evident by an examination of the soil and subsoil; and of the geological formation LAND REQUIRING DRAINAGE. 23 of the situation, and of the surrounding country; except in cases where the source or cause of the wet condition of the land is apparent. The examination of the soil and the subsoil is made by digging large holes down several feet deep, at distances around the land, or by atrench dug along the sides, (which may afterwards fotm part of the drains,) taking care to examine especially such parts as either in reference to the quantity of water present, or the conformation of the surface, appear to indicate the probability of variation in the substrata. This examination should be made to a depth of five feet at least, if the nature of the ground permit; but if the surface soil is a shallow layer upon rock, the nature of the rock should be examined, and its character, whether of porosity or of impermeability, ascertained. This examination as to the soil, if deep, will enable the drainer to arrive at some approximate idea of the depth at which the water is impeded, and the course of its flow beneath the surface, if it be not stagnant. The geological examination is, however, by'no means easy even to the experienced eye. The distribution of soils upon the surface of the earth, is very various as to quality, texture, and thickness. The formation of the subjacent rocks on which they rest, is no Iess so. The direction of the rocky strata as to their inclination, or -" dip," as if is called, is also changeable and endless. Some strata are porous, readily admitting the passage of water; others in a much less degree so; and again others, whilst they are impervious to water, as regards their solidity, are filled, nevertheless, with fissures and cracks, which permit the free ingress and egress of the water through them. It will be obvious, therefore, that 24 LAND REQUIRING DRAINAGE. the great secret which it is desirable to the drainer to ascertain, is the effect of these numerous, and often conjointly operating causes, upon the course of the water with which he has to deal. In level districts of country, the examination of the surface and the subsoil is usually sufficient to direct to tolerably satisfactory conclusions for practical purposes; but'in hilly and mountainous districts, it will be evident that the underground aqueous currents must be dependent upon a multiplicity of circumstances, the effects of which can only to a limited extent be understood, whilst still such of them as can be'unravelled, afford valuable information to guide the operations of drainage. In order to give some general ideas on the subject, the following extract from a valuable article on Drainage is given, which will afford data upon which to found more particular observations of different localities: "Should a mountain consist of concentric layers r different rocks arranged mantle-shaped around it, then water will descend between the lines of junction of the rockes; and should the masses or beds of rock be of different extents, and thickness, and consistence, then the wister will either appear at the surface of the ground as a spring, from the subjacent rock of a close texture, or it will descend yet lower, and be absorbed by the subjacent rock of a porous texture. In this manner the harder rocks cause the springs to appear at a high elevation, while the porous ones convey the water to a lower level, until it meets with a resisting substance to cause it to come to the day. In any case the farmer cannot do any thing until the water indicates its pres LAND REQUIRI1NG DRAINAGE. 25 ence on the surface of the ground, either at a high or low elevation; and then he should take measures accordingly to remove it. "To illustrate the cases now alluded to, suppose,. I! HI' Fig. 4 to represent a hill composed of different rocks of different consistence. Suppose the nucleus rock a to be of close texture, when the rain falls 2 h: ~ ~~~~~.o., Fig. 4 to rpresent a hll composedof differen rocs f dffret cossne ups h ulu roc k 1 a to beo coetetr, we h ri al 2r 26 LAND REQUIRING DRAINAGE. upon the summit of the hill, which is supposed not to be covered with impervious clay, but with vegetable mould, the rain will not be absorbed by a, but will pass down by gravity between a and b, another kind of rock of close texture. When the rain falls in greater quantity tihan will pass between these rocks, it will overflow the upper edge of b, and pass over its surface down to c; but as c is a continuation of the nucleus impervious rock a, a large spring will flow down the side of the hill from c, and render the ground quite wet to d, where, meeting another large stratum of impervious rock, it will burst out to-day a large spring at d, which will be powerful in proportion to the quantity of rain that falls on the mountain. On flowing down b; part of the water will be intercepted by the rocks f and g, both of which, being porous, will absorb and retain it until surcharged. The surplus water meeting with the impervious rock e, will be partly thrust out to-day along the black line d h, on the one hand, and d i on the other, when the whole line h i -will present a long dark line of wet oozing out of the soil, with the spring d in the centre, and which darkness and dampness will extend down the inclined ground as far as the upper line k Z of that porous stratum of rock. Part of the water absorbed by the porous rocks f and g will be conveyed under the impervious rock e, and come out at their lowest extremities, following the curved dotted lines h d and d i, and continue to flow on until it reaches the lowest extremity of e in the. dotted line k 1, where it will be absorbed by' the porous rock m. "By such an arrangement of rocky strata on the side of a mountain range, will be exhibited specimens of both LAND REQUIRING DRAINAGE. 27 wetness and dryness of soils. The summit a will be wet, and so will the surface of b, but the surfaces off and g will be dry. Again, the surface of e will also be wet, but less so than that of b, because part of the water is conveyed by f and g under e to the dry stratum k i, which being probably thicker, and, at all events, of greater extent, will be drier than eitherf or g. On another side of the surface of the hill another result will take effect. The rain falling on the summit a will descend between a and n, as far as the lowest extremity of n along the dotted line op, which being-under the impervious rock e, the water will continue to flow out of sight until it descends to k 1, where it will be absorbed by the porous rock m, and thus never appear at all either as a spring or a line of dampness. But should the quantity of rain -at any time be greater than what will pass between a and n, it will overflow n and be absorbed in its descent by the porous rock f, which, after becoming surcharged, will let loose the superfluous water in the line h r, upon the continuation of the rock n, part of which will come to-day along the line h o of the imperious rock e, and part conveyed down by o p to the porous rock k 1, where it will be absorbed. Thus, on this side of the hill, as long as little rain falls, none but its summit will be wet, and all the rest will be dry, though the surfaces of f and k will always be drier than those of n or e; but after heavy rains dampness will show itself along the line h r, and will.extend itself even to the line of k i, should the rain. continue to fall some time. "The line s by the summit a to t is the mould line pervious to moisture, and which is here represented as is frequently exhibited in nature, namely, a thickness 28 LAND REQUiRI~ G DRAINAGE. of soil on the southern side of the hill, as from a to i, and a thickness of soil on the northern basis, as from r to s; but a thinness of soil on the southern face, as from a to r. It is not pretended that this figure is a truly geological portrait of any mountain. But such overlying and disconnected strata do occur over extended districts of hilly country which produce springs much in the way described. Similar courses of water occur in less elevated districts, though it remains more hidden under the deeper alluvial rocks."* From the foregoing diagram explanatory of the geological distribution of soils, and of the strata upon which they rest, it will be evident that if a section be cut through ground which slopes, it will frequently happen that the substrata lying more or less horizontally will "crop out," or strike the slope as it is ascended, at right angles, or nearly so, as is shown in the figure. Fig. b. TB USiUAL POSITION OF SUBSTRATA IN REFBRNCE TO TIHE BOULA 80o. Bearing, in mind the preceding remarks upon the passage of water through strata of various degrees of permeability, it will be obvious that when water from the top of the slope has sunk through such of the upper strata as are porous, and in its. descent comes to strata that, from their closer texture, oppose its downward course,' it will flow along such strata until the body of the latter becomes saturated, and the * Stephens. LAND REQUIRING DRAINAGE. 29 surplus water will then come out upon the slope and run down its face. It will be perceived, from the brief view which has *been taken, that the principal causes of mischief to u ndrained land arise from one or more of the following conditions: 1. Where water has accumulated beneath the surface, and originated springs; 2. Where, from the close nature of the substrata, it cannot pass freely downward, but accumulates, and forms its level, or water-line, at a short distance below the surface: and, 3. Where, from the clayey or close texture of the soil, it lies on the surface, and becomes stagnant. The preliminary examination of the ground above directed, is made with the view to ascertain as nearly as possible whether the water to be got rid of proceeds from one or more, and which, of the above causes. Swamps, bogs, and morasses, generally are occasioned by the first and second of the above conditions; and that surface-wet state, that often prevails in tenacious soils, that have a comparatively even level appearance, usually arises from the last cause named above. CHAPTER II. TEE VARIOUS SYSTEMS OF DRAINAGE. UPON the cause which is found (from the examination of the land recommended in the preceding chapter) to produce the water that is to be drained away,'will depend the system of drainage that it is most expedient to adopt, in order to remove it. There are three systems of drainage which have been most in use. These are,' Surface Draining, Frequent or Thorough Draining, and Deep Draining. Surface Draining consists in cutting channels for water to pass through upon the surface, which are left as permanent open ditches. Frequent, or Thorough Draining, or Under-draining, as it is often called, consists in opening numerous drains at various depths near the surface, or not below three or four feet from it; and filling them again, after providing a duct for the passage of water at the bottom of them, either open or formed of porous materials. Deep Draining consists in making drains in the same manner as for Frequent or Thorough Drains, but much fewer in number, and placed at greater depthsfrom four or five to eight feet, or even more, according to the nature of the ground and the formation of its surface line. This is called, also, " Elkington's System," from the name of its originator. For the purpose of intercepting springs and deeplyseated masses of water, the value of deep draining is (80) VARIOUS SYSTEMS OF DRAINAGE. 31 generally acknowledged; but its efficiency, as compared with the system called Thorough Drainage, for the purpose of removing water present, or falling upon the surface in the shape of rain, in subsoils of a stiff, clayey character, and for keeping such soils in a favorable state for agricultural purposes, has been made matter of great dispute with professional drainers of eminence. It may serve to elucidate the question of tl:e comparative advantages of the two systems, to state in as few words as possible the principal features in the dispute between the advocates of each. The deep drainers contend that, as water always seeks the lowest level, the deeper the drain is placed, the lower must be the under-ground water- tine, or level of surplus water; because, the water that passes down from the surface to the depth of the drain, can only accumulate below it; for, as soon as it has risen below it to the level of the bottom of the drain, it -will then enter the drain at the bottom, through its porous material, and be carried away by it. Consequently, they say, the deeper the drain, the greater will be the mass of thoroughly-drained soil above it. This is undoubtedly correct, provided the deep drains be near enough together, and the soil above them be porous enough to allow of the passage of water through with sufficient rapidity to keep the surface usually in a fit state for agriculture. In many soils and situations, it may be the case. But if the subsoil be of a stiff, clayey, or very tenacious nature, the shallow drainers contend that thorough or fivquent drainage becomes the most efficient; because, they conceive that the water cannot descend far below the surface in clay; and that it is either held, therefore, in 32 VARIOUS SYSTEMS OF DRAINAGE. suspension by the soil, or, if saturated, that it remains on the surface, and that it does not pass through to deep drains below. And this may be so in very stiff soils, so fax, at least, as to render it impracticable, (looking ai the quantity of falling water to be got rid of in a given time,) to prevent the water-line rising nearer to the surface than is desirable, from the slow rate at which, in such soils, water percolates downwards. But the idea that water will not slowly continue its passage down through clay, is erroneous. The principle of deep draining is, therefore, not really the subject matter in the dispute, so much as its expediency and practical utility, as compared with more shallow and numerous drains, in some soils and situations. That this is the solution of these different views of the matter, appears to be the fact, from the circumstance, that in many instances in which deep draining has been adopted, after shallow drains had been found ineffectual upon the same piece of land, (and in which, consequently, the two sets of shallow and deep drains have existed together,) it has been ascertained, that after heavy storms, the deep drains have given out water long after the shallow ones ceased to do so. It is clear, therefore, that had the deep drains been absent, the shallow drains could only have taken the water away which was above, or on the same level with themselves. But ithas been wrongly called by the advocates of either side a dispute about deep draining, and frequent or thorough draining: for as Elkington's deep drainage provides for the free passage of water by open subterranean ducts, and as Smith, of Deanston, (the great promoter of the system known as thorough draining,) VARIOUS SYSTEMS OF DRAINAGE. 33 directs especially the placing of an impervious material over the drains to prevent the downward passage of water directly into them from the surface, the mode of operation of those drains is the same as that of drains cut deeper- and at greater distances apart; whatever may be the relative advantages of the two systems asto their efficiency. The dispute in reality has been, What is the true way in which the drains act? And the questions put in issue by the parties may be stated thus: Whether deep drains on the Elkington system are applicable to all cases; those arising from the pressure of springs or stagnant water, and those arising from surplus surface or rain water, in stiff soils and subsoils? And whether, assuming that frequent drainage is a preferable system for the latter class of cases, this frequent drainage should be at a depth of three feet as a maximum, as advocated by the shallow drainers, or that four feet should be a minumum depth, as advocated by the deep drainers? And further: What should be the distance apart of the drains? These are the questions now remaining at issue between the most eminent drainers in England. In some situations, where, for instance, the examination of the land showed that springs from high ground were partly the cause of the evil, and the nature of the substrata another, it would be right to cut off the springs upon Elkington's system, and then drain the land generally upon the frequent drainage principle. The system of surface drainage, by open drains, requires no particular notice in this chapter, as its mode of action is self-evident. We will now proceed to explain the above systems, and the method of carrying them out. 2* CHAPTER III. DEEP DRAINAGE. THIE system of deep drainage, is called Elkington's method, having originated with Mr. Joseph Elkington, a farmer, who resided in Warwickshire, England, and was first practiced by him about 1764. His fields being very wet, and rotting many of his sheep, he dug a trench four or five feet deep, with the view of discovering the cause of the wetness. Having a suspicion that the drain was not deep enough, he forced an iron crowbar four feet below the bottom of the trench, and, on pulling it out, a great quantity of water welled up through the hole it made. He was led to infer from this, that large bodies of water are pent up in the earth, and constantly injuring the surface-soil, but which may be let off by tapping with an auger or rod. This discovery introduced a complete revolution in the art of draining. The principles of Elkington's mode of draining seem to depend on these three alleged facts: 1. That water from springs is the principal cause of the wetness of land, which, if not removed, nothing effectual in draining can be accomplished. 2. That the bearings of springs to one another must be ascertained before it can be determined where the lines of drains should be opened; ana (84) DEEP DRAINAGE. 35 by the bearings of springs, is meant that line which would pass through the seats of true springs in any given locality. Springs are characterized as true which continue to flow and retain their places at all seasons; and temporary springs consist of bursts of water, occasioned either by heavy rains, causing it to appear on the surface sooner, or at a hiygher level'than permanent springs, or by true springs leaking water, and causing it to appea. on the surface at a lower level than themselves; and, if such springs are weak, their leakage may be mistaken for themselves. It is evident, that if drains are formed through these bursts of water, no effectual draining takes place, which can only be accomp)lislled by the drain passing through the line of true.i)rings. 3. That tapping the spring with the auger is aL necessary expedient, when the drain cannot be cut deep cWugh to intercept it.* The causes of' the wetness of land, to remedy which this system was put forward, were primarily those arising from springs, and oozings of water issuing from elevated and hilly districts of ground, the characters of which frequently prove the means of rendering the grounds below wet and swampy; for the general moisture of the atmosphere being condensed in'much greater quantities in such elevated situations, the water thus formed, as well as that which falls.in rain, and sinks through the superficial porous materials, readily insinuates itself, and thus passes along between the first and second, and still more inferior strata, which compose the sides of such elevations, until its descent is retarded, or totally obstructed by some impenetrable * Johnston on Elkinzton's Mode of Draining. 36 DEEP DRAINAGE. substance, such as clay. It there becomes dammed up, and ultimately forced to filtrate slowly over it, or to rise to some part of the surface, and constitute, according to the particular circumstances of the case, different watery appearances in the grounds below. These appearances are oozing springs, bogs, swamps, or morasses, weeping rocks (from water slowly issuing in various places), or a large spring or rivulet, from the union of small currents beneath the ground. This is obvious from the sudden disappearance of moisture on some parts of lands, while it stagnates, or remains till removed by the effects of evaporation, on others; as well as from the force of springs being strongerin wet than in dry weather; breaking out frequently after the land has been impregnated with much moisture in higher situations, and as the season becomes drier ceasing to flow, except at the lowest outlets. The force of springs, or proportion of water which they send forth, depends, likewise, in a great measure, on the extent of the high ground on which the moisture is received and detained, furnishing extensive reservoirs, or collections of water, by which they become more amply and regularly supplied. On this account, what are termed bog springs, or such as rise in valleys and low grounds, are considerably stronger, -and more regular in their discharge, than such as burst forth on the more elevated situations on the sides of eminences.* In order to remove the evil consequences referred to, caused by water passing between the porous and impervious strata of mountains and hills, and producing springs, the mode of draining is that of intercepting * Johnston on Draining. DEEP DRAINAGE. 37 the descent of the water or spring, and thereby totally removing the cause of wetness. This may be done where the depth of the superficial strata, anA consequently of the spring, is not great, by, miVlng horilIg. 6......-..: —----—'2.. zontal drains (Fig. 6, a) of cod'siderable length across the declivities of the hills, about where the low grounds of the valley begin to form, and,connecting these with others, b, made for the purpose of conveying the water thus collected into the brooks or rivulets, c, that may be near. Where the spring has naturally found itself an outlet, it may frequently only be necessary to bore into it, e, or render it larger and of more depth; which, by. affording the water a more free and open passage, may evacuate and bring it off more quickly, or suit it to a level so greatly below that of the surface of the soil, as to prevent it from flowing into or over it. Where the uppermost stratum is so extremely thick as not to be easily penetrated, or where the springs formed by the water passing from the higher grounds may be confined beneath the third or fourth strata 38 DEEP DRAINAGE. of the materials that form the declivities of hills or elevated grounds, and by this means lie too deep to be penetrated by the cutting of a ditch, or even by boring, the common mode of cutting a great number of drains to the depth of five, six, or more feet across the wet morassy grounds, and afterwards covering them in such a manner as that the water may suffer no interruption in passing away through them, may be practiced with advantage; as much of the prejudicial excess of moisture may by this means be collected and carried away, though not so completely as by fully cutting off the spring.* In the drainage of wet or boggy grounds arising from springs of water beneath them, a great variety of circumstances are necessary to be kept in view. Wet grounds of these kinds may be arranged under three distinct heads: First, such as may be readily known -by the Fig. 7. I t, O springs rising out of the adjacent more elevated ground in an exact or regular line along the higher side of the wet surface. Secondly, those in which the numerous * Loudon. DEEP DRAINAGE. 39 springs that show themselves are not kept to an exact or regular line of direction along the higher or more elevated parts of the land, but break forth promiscuously throughout the whole surface, and particularly towards the inferior parts, (Fig. 7, a,) constituting shaking quags in every direction that have an elastic feel under the feet, on which the lightest animals can scarcely tread without danger, and which, for the most part, show themselves by the luxuriance and verdure of the grass about them; and, Thirdly, that sort of wet land from the oozing of springs, which is-neither of such great extent, nor, in the nature of the soil, so peaty as the other two, and to which the term bog cannot be strictly applied, but which, in respect to the modes of draining, is the same.* In order to direct the proper mode of cutting the drains, or trenches, in draining lands of this sort, it will be necessary for the draining engineer to make himself perfectly acquainted with the nature and disposition of the strata composing the higher grounds, and the connection which they have with that which is to be rendered dry. This may, in general, be accomplished by means of levelling, and by inspecting the beds of rivers hthe edges of banks that have been wrought through, and such pits and quarries as may have been dug near to the land. Rushes, alder-bushes, and other coarse aquatic plants, may also, in some instances, serve as guides in this business; but they should not be too implicitly depended on, as they may be caused by the stagnation of rain-water upon the surface, without any spring being present. The line * Johnston on Draining. 1* 40 DEEP DRAINAGE. of springs being ascertained, and also some knowledge of the substrata being acquired, a line of drain (F;. 7 b b) should be marked out above or below thenm, according to the nature of the strata, and excavated to such a depth as will intercept the water in the porous strata before it rises to the surface. The effect of such Fig. 8. \ -... ~..-... drain wil often be greatly heightened by boring holes drain will often be greatly heightened by boring holes in their bottom with the auger. Where the impervious stratum (Fig. 8, a) that lies immediately beneath the porous, b, has a slanting direction through a hill o rising bank, the surface of the low lands will, in general, be spongy, wet, and covered with rushes on every side, c. In this case, a ditch or drain, d, properly cut on one side of the hill or, rising ground, may remove the wetness from both. But where the impervious stratum dips, or declines more to one side of the hill or elevation than the other, the water will be directed to the more depressed side of that stratum; the effect of which will be that -one side of such rising ground, will be wet and spongy, while the other is quite free from wetness.* * Loudon on Draining. DEEP DRAINAGE. 41 In cases where the banks or rising grounds arefor tedcd in an irregular manner (Fig. 9), and from the nature of the situation, or the force of the water underneath, springs abound round the bases of the protuberanllces, the ditches made for the purpose of draining should always be carried up to a much higher level in the side of the elevated ground than that in which the water or wetness appears, as far even as to the firm, unchanged land. By this means, the water of the spring may be cut off, and the ground completely drained; which would not be the case if the trench or drain were formed on the line of the loose materials lower down, Pig. a where the water oozes out; which is liable to mislead the operator in. forming the conducting trench, or that which is to convey the water'from the cross-drain on the level of the spring to the outlet or opening by which it is discharged (Fig. 9). But where the main or principal spring comes out of a perpendicular or very 42 DEEP DRAINAGE. steep bank, at a great height above the level of the outlet into which it may discharge itself by nm.ll,.. of a drain, it will neither be necessary, nor of any utility, to form a deep trench, or make a covered drain all the way from such outlet up to it; as, from the steepness of the descent, the water would be liable, when the drain was thus cut from the thin strata of -sand and' other loose materials always found in such cases, to insinuate itself under the bricks, stones, or other substances of which the drain was formed, to undermine and force them up by the strength of the current; or, probably, in some instances, block the drain up by the loose sand, or other matters which may be forced away or carried down by it. In situations of this kind, Johnston observes, it is always the best way to begin just so far down the bank or declivity as, by cutting in a level, the drain may be six or seven feet below the level of the spring; or of such a depth as may be requisite to bring down the water to a level suitable to convey it away without its rising to the surface, and injuring the lands around it.'The rest of the drain, whether it be made in a straight or oblique direction, need not be deep; and may, in many instances, be left' quite open; it should, however, be carefully secured from the treading of cattle, and, where the land is under an arable system of cultivation, also -from the plough. Where it is covered, the depth of about two feet may be sufficient. There will not, in such drains, be any necessity for the use of the auger in any part of them.* In the cases of hills covered with stiff clay and tenacious soils, where the large quantity of water falling on * Loudon. DEEP DRAINAGE. 43 their surface cannot sink into them, but flows down over the surface, the mode of draining them is shown by reference to Fig. 10. The hill in Fig. 10 being supposed to be covered sad- dle-shaped with an imper- I vious stratum of clay, no water can descend into it, but will flow over it: a is the,' clay stratum; b also an im- i pervious stratum, but not so much so as a, containing veins of sand and nodules i of stones. It is clear that the whole extent of ground ~ | from e to b will be wet on the surface, and the wetness will not exhibit itself in i1 1 illli i bands, but be diffused in a 1I! I uniform manner over the 9 Ii whole surface; but as b, in \ i this case, is not so tenacious as a, the side of the hill from e to c will always be,j wetter than the flat ground from c to b, because some of the water will be absorbed 7 and kept out of sight in the looser clay b. The only method of intercepting the large body of water in its descent down d is to cut the deep drain at c, not only sufficiently large to contain all the water that may be supplied from above c, but so deep as to catch any oozing of water from a toward b. What the depth of 44 DEEP DRAINAGE. this drain should be, it is not easy to determine without farther investigation, and to enable that investigation to be made, a large drain should be cut on the flat ground in the line from b: to c, which will also answer the purpose of leading away the water that will be collected by the transverse drain c. Suppose the subsoil from b to i is four feet thick, then this leading drain should be made one-half foot deeper, namely, four and a half feet, in order that its sole may be placed in impervious matter; and in this case, the drain c, of the depth of six feet, may suffice to keep the flat ground dry. But if from b to i is eight or ten feet in depth, then it would be advisable to make the leading drain from b to c at least six feet deep, in order to drain a large extent of ground on each side of it, and the drain c may still do at its former depth, namely, six -feet. Should the bottom of the leading drain get softer and wetter as the cutting descends, its depth should either be carried down to the solid clay at i, or perhaps it would be well to try auger holes in the bottom, with the view of ascertaining whether the subjacent water might not rise to and flow along it. The expedient of boring will be absolutely necessary, if the depth from b to i decreases as the distance from the hill increases, for there would be no other way of letting off the water from the basin of the clay from i to c. Should the flat ground be of considerable extent, or should the face of the plain undulate considerably from right to left, a leading drain will be required in every hollow; and each of them should be made deeper or shallower, according as the subsoil is of an open texture or otherwise, bearing in mind that the bottom or sole of the drain should, if plossible, rest upon an impervious substance, otherwise the DEEP DRAINAGE. 45 water will escape through the pervious matter, and do mischief at a lower level. The subsoil between g and It, being supposed to be gravel, or other porous substance, it is clear that'no drain is required at f to protect the soil between f and g, as the porous subsoil will absorb all the water as it descends from e to f. As to the wet surface of the hill itself c d eJ it being composed of impervious clay, must be dried on the principle of surface-draining; that is, if the ground is in permanent pasture, a number of transverse open* sheep drains should be made across the face of the hill, and the water from them conveyed in open ditches into the great draim c; or if the ground is under the plough, small covered drains will answer the purpose best; and the contents of these can be emptied into the large drain c, and conveyed down the large leading drain to b. Thus in Fig. 11, a b is the main drain along the flat ground into which the large drain c b and d b flow. It may be observed here that when one large drain enters another, the line of junction should not be at right angles, but with an acute angle in the line of the flow of water, as at b. The open surface-drains in permanent pasture exhibit the form - as represented in this figure, where the leaders e f and g h are cut with a greater or less slope down the hill according to the steepness of the acclivity, and the feeders across its' face nearly in parallel rows, into their respective leaders. In this way the water is entirely intercepted in its descent down the hill. Where small drains enter larger, they should not only enter with an inclination, as remarked above, but where they come from'opposite sides, * See Chap, on different kinds of drains 46 DEEP DRAINAGE. as in this case, they should enter at alternate.distances, as seen in the case of the three drains above fJ and not as shown in the fourth and fifth drains. The large Fig. 11. A PLAN OF nIEEP DRAINS OS A HILL OF IMPEBIOU1S SBUMOIi. drain c b d may either be left open or covered. Should it form the line of separation between arable ground and permanent pasture, it may be left open, and serve to form a fence to the hill-pasture; but should the entire rising ground be under the plough, this, as also the main drain a b, and all the small drains, should be covered.* Where springs, or oozings of water, rise around gravelly eminences, standing isolated upon a bed of clay, or other impervious matter, a circumvallation of drain around the base of the eminence, begun in the porous, and carried into the impervious substance, having a depth of perhaps from five to seven feet, and connected with a main drain along the lowest quarter of the field, will * Stephens. DEEP DRAINAGE. 47 effectually dry all the part of it that was made wet by the springs or oozings. Bogs and marshes have been drained with great effect by Elkington's method, which rested on basin-shaped hollows in clay; and, when this is of considerable depth, the only way of draining them is by bringing up a deep cut from the lowest ground, and passing it through the dam-like barrier of clay. But it not unfiequently happens, that gravel or sand is found at no great depth below the clay on which bogs rest; in which case, the most ready and economical plan, is to bore a hole or holes, in the first instance, through the clay, with an auger five inches in diameter, and, after the water has almost subsided, to finish the work by sinking wells through the clay, and filling them up with small stones, to within two feet of the top.* * Stepher CHAPTER IV'. FREQUENT OR THOROUGH DRAINAGE FREQUENT or Thorough Drainage is effected by means. of small drains, placed under ground, at short distances from one another, and into which the water, as it falls upon the surface, or already present, finds its way through the porous soil, and by which it is conveyed by main drains, made in connection with the small, to an outlet. This, system of drainage was, about the year 1832, brought prominently into notice by James Smith, Esq., of Deanston, Sterlingshire, in Scotland, as providing frequent opportunities, both for the water rising from below, as well as for that falling on the surface, to pass freely and completely off; and hence the name of Frequent Draining, which has been given it. Mr. Smith states that in Scotland, much more injury arises to land there from the retention of rain-water, than from springs; and he, by implication, treats Elkington's Deep Drains as efficient for remedying wetness arising from the latter, but the Thorough Drainage as especially applicable to the former, and as effective for both, under ordinary circumstances. The principal things for consideration, in order to carry out efficiently the system of frequent or thorough drainage of land, are:(48) FREQUENT OR THOROUGH DRAINAGE. 49 FIRST.-The situation of the drains and their fall, or the inclination at which they are to be made to ensure the ready passage of water, through them. SEcoND.-Their size and depth. THIRD.-Their distance apart. As to the situation of the drains, the small drains are distributed at intervals over the whole surface of that part of the ground which requires drainage, and the main drains into which they empty themselves are placed on the lowest part of the ground. The first, and a most important question in placing drains, is the direction in which they should run with regard to the inclination of the surface of the ground. This subject is another "vexed question" between experienced drainers; but certainly in this instance the one side of the argument has undoubtedly the advantage. This question has been, whether the small drains which first collect and receive the water from the land should be placed across the slope of the land, or down the slope. The latter is the proper direction. Because in cutting drains across a sloping surface, in cases where the different substrata " crop out" upon the slope (see Fig. 5, page 28,) unless they are put in at the precise point where the substrata so crop out, (and these are very irregular in point of thickness), they may, in a great measure, prove nugatory. For although one drain is neai another, from the rise of the ground none of them may reach the point sought, whereas in carrying a drain up the direction of a slope, it is impossible to miss the extremity of every substratum passed through. This view of the direction of drains is supported by Mr. Smith, who says, " drains drawn across a steep, cut 3 50 FREQUENT OR THOROUGH DRAINAGE. the strata or layers of subsoil transversely; and, as the stratification generally lies in sheets at an angle to the surface, the water passing in or between the strata, immediately below the bottom of one drain, nearly comes to the surface before reaching the next lower drain. But as water seeks the lowest level in all directions, if the strata be cut longitudinally by a drain directed down the steeps, the bottom of which cuts each stratum to the same distance from the surface, the water will flow into the drain at the intersecting point of each sheet or layer, on a level with the bottom of the drain, leaving one uniform depth of dry soil."* And the accuracy of Mr. Smith's observations is demonstrated by Mr. Stephens in the following illustrations and remarks: " Without taking any other element at present into the argument than the single proposition in hydraulics that water seeks the lowest level in all directions, I shall prove the accuracy of Mr. Smith's conclusions by simply referring to Fig. 12, which represents a part of a field all having the same, and that a steep, declivity, and which is laid off in the ridges a b c d ef, up and down the slope; but the three ridges a b c have drains across them, and the other three ridges have drains parallel with them, the oblique drains being made at the same distance from each other as the up and down ones, whatever that distance may be. Now, when rain falls on and is absorbed by the ridges a b c d e f, it will naturally make its way to the lowest level, that is, to the bottom of the drains; and, as the ground has the * Smith on Thorough Draining. FREQUENT OR THOROUGH DRAINAGE. 51 same declivity, the water will descend according to the circumstances which are presented to it by the positions of the respective systems of drains. On the ridges d e ki.. I f having the drains parallel to them, and up and down the inclination of the ground, the water will take a diagonal direction towards the bottom of the drains, as 52 FREQUENT OR THOROUGH DRAINAGE. indicated by the deflected arrows at k. Whereas on the ridges a b c, which have oblique drains, a, 1, g, Fig. 12, the water will have to run in the direction. of the arrows b and h, in doing which it will have to traverse the entire breadth of the ground betwixt a and 1 or I and g, just double the distance the other drains have. Mr. Thomson, of Hangingside, Linlithgowshire, drained 150 acres of land having an inclination varying from 1 in 10 to 1 in 30. Portions of three fields had drains put into them in 1828, 1829, and 1830, in the oblique direction, and, finding them unsuccessful, he put them in the direction of the slope, like the rest of the fields.'In order,' says he,'to ascertain the cause of these failures, a cut was made in the field first referred to, entering at a given point, and carrying forward a level to a considerable depth, when it was clearly seen that the substrata, instead of taking in any' degree the inclination of the surface, lay horizontally, as represented in Fig. 5.' "* It will be observed, from what has been said relative to the direction of drains with regard to the inclination of the surface, that if the land slopes in different directions, then each plane of inclination should have. a system of drainage for itself With regard to the positions of the main drains, as they are intended to carry away accumulations of water from the smaller, they should occupy the lowest parts of the land. If the field is so flat as to have very little fall, the water may be drawn toward the main drains by making them deeper than the other drains, and as deep as the fall of the outlet will allow. If the field have * Stephens. FREQUENT OR THOROUGH DRAINAGE. 53 a uniform declivity one way, one main drain at the bottom will answer every purpose; but, should it have an undulating surface, every hollow of any extent, and every deep hollow of however limited extent, should be furnished with a main drain. No main drain should be put nearer than five yards to any tree or hedge that may possibly push its roots toward it. The small drains should generally be placed nearly at right angles to the main drains, and in lines parallel to each other, down the declination of the ground; not that all the drains of the same field should be parallel to one another, but only those in the same plane, whatever number of different planes the field may consist of. In a field of one plane, there can be no difficulty in setting off the small drains, as they should all be parallel, and all terminate in the same main drain, whether the field is nearly level or has a descent. Fig. 3. PARALLEL DRAIlm Ir ACCORDANOR WITH THE SLOPY OF THE GBOUND. It is not necessary, in all situations, to place the small drains precisely at right angles to the main drain. Where the surface varies considerably, it will be proper to let the position of the smal drains be adapted in 54 FREQUENT OR THOROUGH DRAINAGE. places to the fall of the surface. For instance, when the field has an undulating surface, a main drain is carried up the hollowest part of it, and the; small drains are brought in parallels down the inclination to it. Such drains should be cut, as in Fig. 13, up and down the inclined surface b b, toward the main drain, which would occupy the line along the points of junction of the drains b b. The subjoined sketch of a field thoroughly drained, as to the direction and position of the drains, will elucidate the foregoing explanations: a b is.the main drain formed in the lowest head-ridge; and If the field were of a uniform surface, the drains would run parallelto one another from the top to the bottom into the main drain, as those do from a to c, connected as they should be at the top with the drain d e running along the upper head-ridge. But as there may be inequalities in the ground, a very irregular surface cannot be drained in this manner, and must therefore be provided with sub-main drains, as fg and h i, which are each connected with a system of drains belonging to itself, and which may differ in character from each other, as fg with a large double set k Z in connection with it, and h i with only a small single set n; the sub-mainfg is supposed to run up the lowest part of a pretty deep hollow in the ground, and the drains k and I on either side of it are made to run down the faces of the declivities as'nearly at right angles to the sub-main as the nature of the inclination of the ground will. allow, so as always to preserve the natural tendency of water to find its way down the hollow. There is also a supposed fall of the ground from the height above I toward k, which causes the drain at m to run FREQUENT OR THOROUGH DRAINAGE. 55 down and fall into what would be a common drain ht i, were it not, from this circumstancei obliged to be converted into a sub-main. The sub-main f g may be ------- ~ —--- -~ ~I. I -. _ I. ] 1