CALIFORNIA AGRICULTURAL EXPERIMENT STATION CIRCULAR 391V ->* APRIL 1949 APRIL 1949 V WALTER W. WEIR ■ THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA BERKELEY LAND needs draining if DRAINAGE results in more or better crops, or if swamps, ponds, and alkali areas can be made arable by drainage. The DECISION to drain land is usually based on the balancing of COSTS against increased PROFITS, because few drainage projects are justified unless their costs, amortized over a period of years, can be more than met by increased income from the lands drained. This circular tells the farmer about two types of drainage systems and HOW these systems are planned and installed. THE AUTHOR, Walter W. Weir, is Drainage Engineer in the Experiment Station. Land needs draining if, as a result, more or better crops can be produced, or the production costs reduced to a point where the cost of installing a drainage system can be met out of increased profits. The most obvious need for drainage is in swamps, ponds, or alkali areas which are not producing crops but which could be made arable. Most lands, however, which could bene- fit from drainage are already producing crops, but they could be improved by better drainage. It is these lands which offer the greatest economic inducements for improved drainage conditions. There are several less tangible benefits which may be derived from the drainage of particular tracts such as improved health conditions, conveniences, and sightliness, but usually the decision to drain is based on the economics of the proposal; the balancing of costs against increased profits. Poorly drained lands are relatively cold and crops are delayed in their spring growth. Root development is greater, plants are healthier and less susceptible to disease and parasitic injury on well drained soils. Soil structure and tilth are improved, and because of better root de- velopment plants are less susceptible to drought when drainage is satisfactory. ENGINEERING ASSISTANCE Reliable engineering advice in the plan- ning and construction of drains is a rea- sonable insurance that important data will not be overlooked. Many farmers do not have the technical experience necessary to evaluate all of the factors which go into the planning of a drainage system or the means of converting this information into working units. The farmer's first-hand knowledge of local conditions will not be ignored by the engineer. The planning of some drains is a very simple matter and there is little likelihood of serious error in design, but other drains may present complicated problems. The source and amount of water, the direction of water movement through the soil, sur- face and underground soil conditions, available slope and adequacy of outlet must all be known before the most effi- cient and economical system of drains can be determined. Failure to make full use of all available information, including data on the texture and permeability of the soil and subsoil, may lead to errors in location, depth, spacing and size of drains with a conse- quent loss in efficiency or an excessive cost. This does not mean that some farmers should never attempt drainage without trained engineering advice, but rather it is hoped that in this circular some of the fundamental principles of drainage may be explained in such a way that they may be applied without further assistance. SURVEY AND PLAN Before any construction is started it is advisable to make an overall survey and prepare a plan. The survey should pro- vide information leading to the selection of an outlet; on the texture, depth, strati- fication and permeability of the soil; the slope, size and other physical characteris- tics of the area; rainfall and runoff char- acteristics; depth of water table and its fluctuations; salt and alkali content, and finally the actual location of the drainage lines. This information should be put in such form that it can be used for both immediate and future reference. A map showing the location and size of all drains and laterals as they are actually constructed should be made when the work is completed. In California there are two rather dis- tinct and different conditions under which [3] drainage is necessary. These will be re- ferred to as "drainage in humid areas" and "drainage in arid or irrigated areas." It is recognized, however, that the terms "humid" and "arid" are not sharply drawn on the basis of total annual rainfall or on the basis of whether or not the land is irrigated. As it affects drainage, probably the most important single factor in differen- tiating between humid and arid regions is the presence of alkali salts in the soil and subsoil of arid regions. Although many exceptions can be found, more often than otherwise the soils requiring drainage in humid areas are heavy (fine) textured or have relatively impervious subsoils, and the need for drainage is caused by the slowness with which rainfall or surface water penetrates the soil and is carried away through the subsoil strata. On the other hand, the majority of irrigated lands have light (coarse) to medium textured soils with permeable or relatively permeable sub- soils, and the need for drainage is caused by the accumulation of water in the sub- soil (water table) as the result of exces- sive irrigation, seepage or other more or less artificial means; furthermore, arid soils often contain excessive quantities of soluble salts which may accumulate at or near the surface as a secondary result of high water table. COST OF DRAINAGE The purpose of this circular is to dis- cuss two types of drainage systems; open and covered. The economic feasibility of any drain- age undertaking depends to a large degree on what it costs to install the drains. Few projects will be justified unless their costs, amortized over a period of years, can be more than met by increased income from the lands drained. There are, of course, cases where the drainage of small wet areas may cost more than can be justified by the returns from increased yields. Such cases can only be justified by the in- creased convenience in cultivation, or in having uniformly producing fields. These rather intangible values do not, however, bear an important place in comprehensive drainage. The size of the project, the number of Table 1: WEIGHTS AND PRICES OF DRAIN TILE — 1948 Size Clay Concrete Price per foot Weight per foot Price per foot Weight per foot inches 4 6 8 10 12 14 16 18 20 22 24 dollars 0.07-0.12 0.13-0.18 0.20-0.26 0.28-0.38 0.45-0.55 0.60-0.75 0.70-0.90 1.00-1.25 pounds 7 19M 27 34 44 54 100 dollars 0.07-0.12 0.13-0.18 0.20-0.26 0.26-0.36 0.40-0.50 0.45-0.55 0.60-0.70 0.70-1.00 0.80-1.10 1.00-1.50 1.75-2.25 pounds 10 22 27 40 49 65 78 105 131 185 206 [4] feet of tile needed per unit of area, and similar items make it difficult to estimate cost unless all of the details are known. The cost of open drains is largely gov- erned by the cost of labor: they require little in the way of materials. General cost figures may be somewhat misleading in individual cases. All present day cost figures, of course, are subject to change. In California, drain tile is more expen- sive than in the Midwestern states. There are only one or two factories in this state whose principal business is to make clay drain tile, but there are several factories which make drain tile as a side line with other clay products such as sewer pipe, flues, roofing tile and other ceramics. Plants making concrete tile are more nu- merous and can be found in most towns of 5,000 or more population. Tile are sold by the foot or 1000 feet, and usually some discount can be secured in carlots. Prices may be quoted F.O.B. factory, delivered to the job, or to some railroad shipping point. Table 1 may be used as a guide to the cost of clay and concrete drain tile. The cost of hand-dug trenches will vary according to the price of labor, but one may expect a laborer to dig from about 4 to 8 linear feet of trench per hour to a depth of 3 to 5 feet, and wide enough for 8-inch tile. This will vary with such fac- tors as the condition of the soil and the season of the year. Machine-dug trenches are more eco- nomical if there is sufficient work to jus- tify the movement of the equipment into the area. Under favorable conditions machine-dug trenches will cost about one- half the cost of hand-dug trenches. Laying and backfilling will cost ap- proximately 5 cents per foot for 4-, 6-, or 8-inch tile. Stated in general terms, the cost of a completed tile drainage system will be about three times the cost of the tile; in other words, labor costs such as excava- tion, laying and backfilling constitute about two-thirds of the total cost. A few tile manufacturing companies, both clay and concrete, have their own trench excavating machinery. These com- panies sell complete drainage systems in- cluding the outlets, gravel placed around the tile, and other necessary work and accessories at a stipulated price per linear foot. Drainage systems using 6-inch tile, placed 6 to 6% f eet m depth, are cur- rently being installed, complete in all details, in Imperial Valley for about 42 to 45 cents per linear foot or from $60 to $85 per acre depending on the spacing between tile lines. These prices are, how- ever, based on the contractor being able to keep labor and equipment busy over a long period of time. Where manholes, silt boxes, inlets, pumping plants and other structures may be necessary, these add to the overall cost of drainage and are not usually included in the bids for tile or open drain construc- tion. The above are discussed under the heading "Accessories," page 22. The removal and replacement of fences, irrigation ditches, bridges, purchase of rights-of-way, surveying and such are also extra costs. THE OUTLET No system of drainage, large or small, will prove entirely satisfactory or give the maximum results without a good and adequate outlet. The first questions to be answered are : What is to be done with the water that is to be collected in a drainage system? Where is the outlet, and is it satisfac- tory? For community drains where there is considerable water, a natural channel such as a creek or river will in most cases be the ultimate outlet. For individual farms where the quan- [5 tity of water for disposal is small, the outlet may be a community drain or occa- sionally a roadside ditch or low-lymg area sacrificed for the purpose. In irrigated areas the outlet may be an irrigation canal or lateral, provided the drainage water is of such quality that it does not adversely affect the irrigation supply. No one has the right to dispose of drain- age water in such a manner or in such a place that it will inconvenience others. It may be necessary to cross one or more neighbors' property to get a satisfactory outlet. In such cases, the cooperation or at least the permission of the neighbor must be obtained before the work is done. Frequently, neighbors are also interested in drainage and much mutual benefit and reduced costs can be obtained by working out drainage problems together. On the other hand, one does not have the right to obstruct a natural drainage channel or refuse permission to discharge drainage water into a natural channel if that is the route normally taken by the water. The ideal outlet provides a free flow from the drain at all times, and allows for the construction of drains at such depth and capacity as to give satisfactory drainage to the lands where they are needed. Although all of the requirements of the ideal outlet may not always be met, adjustments can often be made so that otherwise feasible projects need not be abandoned. Fig. 1— A well-constructed concrete outlet structure for drain tile. Tile outlets into creeks or natural chan- nels may be submerged for short periods during storms without serious damage. Some drains are planned so that they need not be in operation continuously. Such a condition would be when tide gates are required or where pumping is necessary. Some very satisfactory drains do not have gravity outlets but discharge into pits or sumps from which the water is pumped. Figure 1 shows a tile drain protected by a well-built concrete structure dis- charging freely into an open ditch. TYPE OF DRAIN There is no best type of drain for all conditions. For any particular location, and under any particular set of conditions the type of drain to be used is largely a matter of convenience and economy. Open ditches make the most economical drains for carrying off large quantities of water, and are used for the removal of water standing or flowing on the surface of the ground. Open drains may be effec- tive also in lowering the water table, but on the individual farm they are usually not so convenient as tile drains for this purpose. Open Drains Open drains, or drainage ditches, are able to quickly dispose of large quantities of water. Water which is on the surface of the ground enters an open drain rap- idly because it is not necessary for it first to penetrate into the soil. Open drains are [6] well suited for the collection of runoff from hillsides or areas flooded by heavy or excessive rains. They may also serve as outlets for tile lines when the cost of large size tile becomes excessive. Some of the disadvantages of open drains are that they require land for rights-of-way which might otherwise be farmed. They harbor obnoxious weeds, brush, plant diseases, and rodents; they require consistent maintenance to be fully effective. Drainage ditches may also be a source of danger to stock, and if stock are permitted free access they trample the bottom and side slopes and increase the cost of maintenance. Ditches across culti- vated fields are an obstruction and incon- venience to tillage operations, and are therefore seldom used unless they can be placed along property lines or other rela- tively out-of-the-way places. Covered Drains Drains placed underground and cov- ered with soil offer an efficient and per- manent method of draining farm land. Covered drains usually consist of either clay or concrete tile. The most common covered drain is made of burned clay tile, and since all covered drains function in much the same manner, this type will be discussed in detail. Other types of covered drains, such as mole, box, and stone should not be used in preference to tile. Tile drains lend themselves to more variation in layout than do open drains because they do not interfere with culti- vation. In general, there are four arrange- ments (fig. 2) which can be used either in true form or in combination. There is no best arrangement for all conditions. Each area to be drained must be surveyed and studied to determine its own particu- lar needs. Tile drains usually require a minimum of maintenance; there is no loss in land, and they do not obstruct or hinder normal farm operations. DESIGN OF OPEN DRAIN SYSTEMS For areas of 160 acres or less in humid regions, drains should be designed to re- move from the area about % inch to 1 inch in depth of water in 24 hours. There are places, especially small areas of a few acres, where it may be advisable to in- crease this amount to about 1% inches in depth. For large tracts of several hundred acres, a runoff of % to % inches is usually sufficient. If water reaches the area from sources outside the area to be drained, the entire contributing area should be considered in determining the amount of water to be removed. Conditions of soil tilth, amount and nature of cover and topography are deter- mining factors in the rapidity and amount of runoff. Water moves slowly on gently sloping fields with heavy cover, while on barren or steeply sloping fields it moves more rapidly. The size of ditch necessary to carry a given quantity of water is dependent upon the slope or grade, and to some extent upon the shape of its cross sec- tion. The shape is determined by the texture of the soil through which the ditch is constructed. Drains intended only to remove water from the ground surface or intercept surface runoff may be de- signed to run full at times of maximum runoff. On the other hand, drains intended to lower the water table must be so designed that the water surface in the drain is al- ways below the depth at which it is desired to maintain the water table. Although open ditches may be any size, only relatively small ditches such as the individual farmer is likely to need will be discussed here. [7] J yr ) INTERCEPTING NATURAL ig. 2— Four arrangements for tile drains. Many drainage systems use a combination of two or more arrangements. [8 Side Slopes The angle, or side slope, of a ditch de- pends largely on the type of soil through which it is constructed. In fine grained soils, such as clay, side slopes will stand almost vertical, one-half to one slopes (V2 foot horizontal to 1 foot vertical) are common. In coarser textured soils 1 to 1 or even 2 to 1 may be advisable. Very sandy soils may require side slopes of 3 to 1. In quicksand it is almost impossible to maintain any predetermined side slopes on drainage ditches. In the design of open drains some of the factors to be considered are known, others must be assumed. For example, the rainfall and rate of runoff must be deter- mined, but since they cannot be deter- mined with extreme accuracy, the amount of water which a drain is designed to carry will be only an approximation. If the estimate is too small there will be times when the drain will not carry the runoff as quickly as desired. If conditions are such that overflow cannot be tolerated and the drainage must be rapid, any error in design must be on the side of safety. If overflow can be tolerated for short pe- riods of time, the design may be on the side of economy. The slope, grade or fall of the drain can be accurately determined by measure- ments on the ground. Size of Drain With grade and side slopes decided upon, the problem is to determine the size (depth and bottom width) necessary to carry the estimated quantity of water. Elliott's formula for open drains has been found satisfactory for determining size, and because of its simplicity is more convenient than some other formulas which may, under certain conditions, be slightly more accurate. Elliott's formula is: v=Va /axlV>f (1) where v = velocity of the flow in feet per second. a = area of cross section of the drain in square feet (V2 of the sum of the bot- tom width plus top width multiplied by the depth). p = wetted perimeter in feet (the bot- tom width plus the length of side slopes which will be wetted) . f = fall or grade in feet per mile. Q = quantity of water (discharge) in cubic feet per second. When "v", which was found by use of Elliott's formula, is multiplied by the cross-sectional area of the drain, "a", it will give the quantity of water, "Q", that the drain will carry. av = Q 2) ( \1 Flow Line ^-/ -V — ■.:, » :\ — / \ / -1 V / V /■:■• Fig. 3— Diagram showing relation of width, depth, side slopes and berm in an open ditch. [9] Figure 3 is a dimensional diagram for open ditches. The procedure for computing the size of a ditch is as follows : First determine the quantity of water to be discharged, "Q". This is seldom known accurately because one cannot accurately know the amount of rain that will fall or the proportion which will reach the drain in any given time, but rainfall and other records will assist in approximating the quantity. Some quantity must be assumed, so let us say that we desire a drain which will carry 5 cubic feet per second (approxi- mately 1 inch in depth from 120 acres in 24 hours) . The fall or slope of the drain is known or can be measured. Let us as- sume that this is 5 feet per mile or ap- proximately 1 foot per 1000 feet. Let us also assume that soil conditions are such that we can expect the sides of the ditch to stand on % to 1 side slopes. As a trial, assume that a drain 3 feet wide on the bottom and flowing 2 feet deep will be required. Substitute these values in formula ( 1 ) : The velocity of flow would be 2.8 feet per second, and substituting this value in the formula av = Q we have 8 x 2.8 = 22.4 cubic feet per second. It is readily seen that such a ditch will carry 4% times the required amount, and is therefore too large. In another trial, assume a drain 2 feet wide on the bottom flowing 1 foot deep. Substituting these values in the formula we have: \/2.5 x 7.5 - 2.1 feet per second v = Vaxiy 2 f = V8x7.5 =2.8 p 7.48 4.2 We now have a velocity of 2.1 feet per second, and an area of 2.5 square feet. In the formula av = Q, this gives a capacity of 2.5 x 2.1 or 5.25 c.p.s. This figure of 5.25 cubic feet per second is within % cubic foot per second of the estimated flow, and the difference is on the side of safety. Therefore, one can conclude that a drain 2 feet wide on the bottom flowing 1 foot deep with % to 1 side slope and a fall of 5 feet per mile will be the correct size for a discharge of 5 cubic feet per second. CONSTRUCTION OF OPEN DRAINS Open drains may be constructed by hand, or with machinery such as tractor and scraper, bulldozer or similar rig, or by heavy excavating machines with drag- line, clamshell or dipper buckets. Ordi- narily, the farmer is interested only in those drains that can be constructed with equipment which he has or can readily secure. Hand-dug drains are limited in size to those which can be dug more cheaply by hand than with power machinery, or to drains in places inaccessible to power equipment. The material excavated from open ditches should be either spread out over adjacent areas or placed far enough from the edge that it will not slip back into the ditch. This "berm," left between the edge of the ditch and the toe of the excavated material, should be at least one-half of the top width of the ditch. In figure 4 it may be noted that the excavated material is well placed, and the berm is adequate. In the drainage of irrigated lands, where the depth to the water table rather than the removal of surface water is of major importance, open drains are sel- dom used for the drainage of individual farms. Drains 5 to 8 feet deep may only flow a foot deep. Such a drain will occupy [10 5 or more acres of land for each mile in length. Obviously such a large ditch to carry so small a quantity of water should be avoided wherever possible. Open drains in irrigated areas are, however, entirely practical as outlets for tile, or where the quantity of water is so great that excessively large tile would be required. Figure 4 shows a machine-dug open drain about 6 feet deep which will make an excellent outlet for tile. MAINTENANCE OF OPEN DRAINS Open drains can be kept in efficient working condition only by careful main- tenance. Drains that are allowed to become ob- structed by brush, weeds and rubbish, or whose banks have sloughed in and par- tially filled them are not capable of pro- viding efficient service. Drains should be cleaned out to their original depth and width at least once a year. The amount of work and cost necessary to maintain a drain in proper condition will, of course, depend on how badly it is obstructed. Cattails, tules and similar water-loving plants are particularly bad and may, in a few months, seriously impair the effec- tiveness of open drains. Cost of maintenance may in a few years equal or exceed the original cost of con- struction. Usually, the best or most effective method of maintenance is to use the same tools or machinery that were used in con- struction. Burning and chemicals are sometimes effective in weed control, but the use of chemicals may create a hazard to stock if allowed access to the drain. Fig. 4— Machine-dug open drain for irrigated areas. Note the wide berm between the edge of the ditch and the toe of the spoil bank. [ii] DESIGN OF TILE DRAIN SYSTEMS Kinds of Drain Tile There are two kinds of tile commonly available for drainage in California, namely, clay tile and concrete tile. Both are used extensively, and both are prov- ing satisfactory when they are well made from good material. Clay tile is made in sizes varying from 4 inches to 30 inches in diameter, and most factories carry regular stocks in sizes up to and including 18 or 20 inches. Larger sizes are made to order or sewer pipe is substituted. There is no objection to the use of sewer pipe except that it is made to more rigid specifications, there- fore more expensive. Clay drain tile is unaffected by alkalis or acids, and nowhere in the agricultural areas of California does the ground freeze deeply enough to affect drain tile. Clay drain tile should, however, equal or ex- ceed the minimum crushing strengths specified by the American Society for Testing Materials. Crushing strengths of 1600 pounds per linear foot should be required for drain tile 8 inches or less in diameter, and crushing strengths of 2000 pounds per linear foot for tile up to 16 inches in diameter. Any reliable tile fac- tory will meet or exceed these specifica- tions. Concrete tile used in humid areas where alkali salts are not a factor should meet the same specifications for crushing strength as those for clay tile. In alkali areas, however, particularly if sulfate salts are present, concrete tile should not be used unless, in addition to the required crushing strengths, it meets specifications as to sulfate resistance. Sulfate resistant cement may be used in the manufacture of resistant tile, but if this type of cement is not used the tile should be cured under high steam pressures. Curing of concrete tile, made with ordinary cements, for two hours with steam at 212° F, or for one half hour at 235° F, will be a reasonable assurance that the tile is alkali resistant. Reliable concrete tile manufacturers are familiar with A.S.T.M. specifications and are prepared to meet them. Concrete tile is available in a larger range of sizes than is common for clay tile. Concrete tile 20 inches or more in diameter should be reinforced with steel bars or mesh to meet the crushing strengths required. It is much better that drain tile exceed the minimum strength requirements than to have a single section fail after it is laid. Cracked, broken or otherwise defective tile should never be used. Cracks can be detected by gently striking the tile with a hammer or metal rod. Good tile will have a clear, bell-like ring. Location The location of the main drain is con- trolled largely by the position of the out- let, and the size, shape and slope of the area to be drained. Sometimes a single line is all that is necessary ; in other cases a complete system of laterals is required. The layout of a tile drainage system may be either a natural system or a regu- lar system. In the former, tile lines simply follow the depressions in the ground sur- face, and in the regular system there is a main line with regularly spaced laterals emptying into it from one or both sides in a gridiron or herringbone pattern. In- tercepting drains follow along the base of a hill or terrace and intercept water as it flows from the higher land (fig. 2) . Springs or seepage areas are often "tricky" and may require that the drain be located exactly through the source of the water. It may take considerable in- vestigation to determine just where a spring is located, and a deviation of two or three feet from the correct location may mean the difference between success and failure. Where a regular gridiron or herring- bone system is required, study should be given to the plan in order that not only [12 dAruirf^ftt • w»<^&H*>iAvM/J*"*t» «*u**Vu»*«r «Mth•^llllHl^l•4B^d»M^»(iEI0L^la^^v•^fc1M