342 



THE IRRIGATION AGE. 



DRAINAGE OF FARM LANDS. 



Results of Careful and Extended Investigations by the Gov- 

 ernment for the Benefit of the Farmers. 



BY C. G. ELLIOTT, 



Expert in Drainage and Irrigation, U. S. Department of Agriculture. 



From Farmers' Bulletin No. 187, Courtesy U. S. Department of Agri- 

 culture. 



(Concluded.) 



The irrigator applies water by surface flooding, 

 using such quantities as his judgment and experience 

 may dictate, feeling sure that any excess which he 

 may appdy wll speedily pass down into the earthj, 

 which, under primitive conditions, being dry to a 

 depth of from forty to sixty feet, porous and open, af- 

 fords unlimited drainage facilities. The large amount 

 of leakage from main canals and the surplus from 

 over-irrigation for a time find a ready and harmless 

 exit into the lower soil. Under such conditions the 

 understrata become a waste reservoir which receives by 

 percolation the 'leakage from irrigation canals and the 

 drainage from, over-irrigation, thus securing to the cul- 

 tivator as perfect soil conditions as could be desired. 



Many of these soils contain considerable quanti- 

 ties of soluble (alkali) salts, prominent among which 

 are sodium chloride, sodium sulphate and sodium car- 

 bonate, which originate in the rocks from which the 

 soils are formed. Lands which up to a certain time 

 have produced crops in quantity and quality to which 

 no exception can be taken may, without apparent 

 cause, begin to deteriorate. Upon examination it will 

 be found that the alkali salts have accumulated near- 

 the surface in such strength as to destroy crops that 

 had previously been grown successfully. Upon further 

 investigation as to the cause, it is found that the water 

 in the lower soil has dissolved large quantities of alkali 

 and holds it in solution. The rise of water to a plane 

 at or near the surface from which rapid evaporation 

 takes place results in the deposit in solid form of all 

 the alkali contained in the water evaporated. The 

 active capillary power of the more finely divided soils 

 accelerates the upward movement of the water, the 

 evaporation of which is rapid in arid climates, result- 

 ing in a deposit which constantly increases from year 

 to year. 



The presence of layers of hardpan at irregular in- 

 tervals throughout the upper six feet of the soil, as 

 well as occasional layers of gravel deposit and adobe 

 clays, has had much to do with the deflection and con- 

 centration of soil water. By reason of hardpan layers 

 the excess of water is brought to the surface more di- 

 rectly at some points than at others. Under the action 

 of soil water some varieties of hardpan soften and 

 gradually disintegrate, thus changing the general text- 

 ure of the soil where it exists. The need of drainage 

 of such soils as a preventive of the injuries noted, as 

 well as for the restoration of land to its normal pro- 

 ductive condition, is appreciated. It is not proposed 

 here to discuss at length the varying conditions exist- 

 ing in different localities, but to call attention to the 

 success that has attended the eff8rts of some farmers 

 who have reclaimed land from the effects of seepage 

 and alkali. 



In the treatment of lands of this character it must 

 be remembered that the conditions under which land 

 becomes saturated by seepage are radically different 



from those of rainfall. In irrigated lands the water 

 accumulates at various points by underflow from the 

 .Vaste of irrigation practiced upon more elevated land 

 adjoining, or from leakage of supply ditches which are 

 constructed through previous material. The preven- 

 tion of the accumulation of water in harmful quanti- 

 ties is best accomplished, not by its removal from the 

 soil after saturation of the land, but by intercepting 

 it before it reaches the lower level. A few examples of 

 this kind will indicate that the method most success- 

 ful differs quite materially from that used in humid 

 areas. 



Albert Igo, near Greeley, Colo., has used a series 

 of small wells located at points where water appeared, 

 -linking them into the gravel which lies beneath the 

 saturated soil. The wells consist of curb boxes twelve 

 inches in diameter, made with eight sides, from boards 

 one inch thick. They are sunk from eight to twelve 

 feet deep, the excavations being made with a large 

 auger. The wells have underdrain outlets about three 

 feet deep leading to a surface ditch. The water rises 

 at once in these wells to the height of the outlet pro- 

 videdrand flows away. The soil, which is about five feet 

 deep, is underlaid with gravel, which, through the 

 process of seepage from higher lands, has become sur- 

 charged with water which, by reason of constant press- 

 ure and continual supply from land occupying a higher 

 level, saturates the soil above the gravel. These wells, 

 put in at various points where water appeared, re- 

 claimed at small cost a field which had been given over 

 to grazing land on account of the saturation and 

 alkali. 



This method of draining is regarded as highly suc- 

 cessful by the farmers of the vicinity who have wit- 

 nessed the reclamation of the land so treated. The in- 

 dividual well and drain as used in the work described 

 are shown in Pig. 18. The method is simple. Its 

 efficiency consists in relieving the pressure of the un- 

 derground water at such a depth that it will not con- 

 tinue to force itself upward against the soil, and also 

 in removing such a quantity that the gravel stratum 

 underlying the tract will provide for the remainder. 



Drains upon another plan have been used by J. 

 Hetzel and others in the vicinity of Longmont, Colo. 

 A continuous line of underdrains is laid crosswise of 

 the slope along the upper-border of the lands show- 

 ing seepage. These drains are laid five feet deep, 

 which is regarded as necessary to their success. The 

 subsoil is adobe clay, in which pockets of sand are en- 

 countered which interefere with the laying of the 

 drains. The method of location is shown in Fig. 19. 

 The drains are made of one-inch boards in the form of 

 a continuous box, 6x6 inches in the inside, with no bot- 

 tom. These drains, complete, cost $1 per rod. It is 

 not uncommon in this vicinity to find one drain lo- 

 cated in this manner intercepting sufficient water to 

 reclaim forty to eighty acres of land, where the soil 

 is of a stiff nature. Where soils are open and admit 

 of very free percolation of water the same plan is 

 applicable, but the size of drains must be increased. 

 The quantity of water which it is necessary to inter- 

 cept is greater than is usually suspected, and some fail- 

 ures to obtain good results are probably owing to the 

 fact that the drains are too small. Shallow drains do 

 not accomplish the desired result, nor do drains laid 

 up and down the slope accomplish the work as fully 

 and cheaply as those laid across the slope. 



