208 



THE IERIGATION AGE. 



with respect to their drainage properties, all variations 

 in each class being recognized and requiring drainage 

 treatment according to their several characteristics. It 

 follows that in practice drains are placed from 30 to 300 

 feet apart and from 1% to 4% feet deep. These vari- 

 ous conditions can not be described in sufficient detail 

 to give a clear understanding of the requirements of 

 each soil. In case of doubt regarding the proper dis- 

 tance apart for drains, they may be so placed that in 

 case more perfect drainage is required a line may be 

 laid midway between the lines. In general, close soils 

 which consist largely of clay should have drains from 

 40 to 75 feet apart, and open soils from 80 to 300 feet 

 apart. In the first instance, which is the more frequent 

 system, tiles %y 2 to 3y 2 inches in diameter may be used 

 for laterals, and for the greater distance those 3y% to 5 

 inches in diameter should be used. It may also be said 

 that one line of 5-inch or 6-inch tile may sometimes be 

 used in such a way as to afford good drainage to an 

 entire field. 



Depth of drafns is also a variable distance, depend- 

 ing upon the same soil characteristics. In some cases 

 drains have been laid four feet deep with indifferent 

 results, while drains two and one-half feet deep on the 

 same land have been attended with gratifying results. 

 In general three feet is a proper depth for average soils, 

 yet a depth of two or two and one-half feet produces 

 better results in some soils. Drains should be placed 

 as deep as they will receive the water readily, with four 

 feet the limit in .clay and alluvial soils. Aeration of 

 the soil is one office of the underdrain, and of great 

 benefit to very close soils. In treating such soils it has 

 been found beneficial to provide surface vents to the 

 drains for the purpose of inducing a more rapid circula- 

 tion of air through the drains and soil. In this way 

 some refractory soils have been drained and greatly 

 improved in texture. Shallow drains in such cases serve 

 the purpose better than deep ones. 



LOCATION OF DRAINS. 



To begin with, there must be an outlet suitable 

 for the system of underdrains which it is proposed to 

 construct. A field or farm may sometimes be thor- 

 oughly drained by simply laying tiles in those parts 

 which are uniformly too wet for profitable cultivation. 

 This is on the theory that the other parts have sufficient 

 natural drainage. In such cases main lines should be 

 located in the course of natural surface flow, with due 

 regard also to straight courses. Branch lines should 

 follow the same general law. This does not mean that 

 the curves and crooks which are always found in nat- 

 ural depressions should be followed; straight courses 

 joined by curves should mark the lines for drains. 



Land which requires drainage always lies in nat- 

 ural areas of greater or less size, each having one point 

 to which all the drainage must finally come. These 

 general areas are again divided into subareas, each 

 having its outlet within the limits of the general area. 

 The boundaries of these areas should first be determined 

 and the plans so made that when the drainage is com- 

 pleted the entire tract will have been provided for. A 

 failure to do this is a fruitful source of disappointment 

 in drainage work. The main drain should be located 

 in the natural depression, with subdrains at such points 

 aS will furnish outlets for the tributary section. These 

 are the arteries, as it were, of the whole system. This 

 work may be carried out in two different ways. The 

 first is to locate branch lines so as to reach those parts 

 of the tract which are particularly in need of drainage. 



such as ponds, swales, sags, etc., without special regard 

 to systematic work. This is called random field drain- 

 age. The second is to supplement the primary network 

 by constructing laterals parallel to each other and at 

 equal distances apart, according to the requirements of 

 the particular soil, on the theory that every part of the 

 field requires equal drainage. 



Fig. 9 shows the plan used in draining a tract of 

 480 acres in Iroquois County, 111., which is generally 

 level, but was, before drainage, diversified to some ex- 

 tent by ponds which contained water during six months 

 of the year. The grades upon which the drains were 

 laid were in some cases one-half inch to 100 feet, vary- 

 ing from this to two inches to 100 feet. The object of 

 drainage was to fit the land at a minimum of expense 

 for the production of hay and grains of various kinds, 

 it should be observed that the drains were staked out in 

 a systematic manner. As shown on the plan (Fig. 9), 

 each line is designated by some name by which it is 

 distinguished from others. Its length, as, well as its 

 junction with other lines, is indicated by the number of 

 feet or the station number from the outlet point in each 

 case. This plan also illustrates various methods of loca- 

 tion and arrangement of drains ordinarily required. 

 The drains of this tract have been in successful opera- 

 tion for fourteen years and are admirably adapted to 

 the purpose for which they were constructed. There 

 have been no repairs or stoppages of any .kind during 

 that time. The land is an open black soil with joint 

 clay subsoil which drains quite readily. The final out- 

 lets, as shown, are open ditches leading to the larger 

 water course. 



The most economical system for thorough drainage 

 is that of parallel lines of a good length. This will be 

 readily acknowledged when it is seen that, wherever one 

 drain joins another, the soil in the vicinity of the junc- 

 tion has two drains acting upon it instead of one ; in 

 other words, it is doubly drained. In such soils laterals 

 should be laid up and down the slope and not across it 

 as advocated by many. It would doubtless seem in- 

 credible to those who find it necessary to place drains 

 only forty feet apart that other soils may be drained 

 as thoroughly with parallel lines 100 feet or even 200 

 feet apart. In the latter case, however, the laterals 

 should be not less than four or five inches in diameter. 



While, as a general rule, drains should be laid up 

 and down the slope, there are special cases where the 

 other plan is more effective and will accomplish the de- 

 sired end at less cost. A case of this kind is illustrated 

 in Fig. 10, which shows a pond surrounded by lands 

 with steep slopes. The subsoil of the sloping land is 

 open and porous, absorbing the rainfall readily and per- 

 mitting water to flow through to the base of the slope, 

 where, being checked, it accumulates and forms a bor- 

 der of wet ground around _ 

 the outer edge of the pond. 

 The line located through 

 the center of the pond does 

 not affect this wet strip, 

 since the soil at the outer 

 edge of the pond is less 

 pervious to water than the 

 soil of the hillside. By rea- 

 son of this resistance and 

 the continual head of water 

 supplied by the hill, the 

 base is kept saturated. An 

 intercepting drain laid near 

 the base, as shown in the illustration (Fig. 10), is the 







Fig. 10. Intercepting Drain. 



