DEAINAGE OP IRRIGATED SHALE LAND. 



15 



where the two most important lines should be located — one 120 feet 

 from and parallel with the east fence line, and the other 45 feet from 

 and parallel with the south fence line. 



In the location of drains in those lands underlain by hard and 

 practically impervious shale interception methods can be used, pro- 

 vided the shale surface is even and sufficiently near the ground sur- 

 face to be reached by a tile drain throughout the entire length of 

 the line; otherwise this method can not be used, and the overlying 



Test We//s O Ground Surface > — 106 — -^ 



Floyvin^ Test Wells-M Shale Surface^ ^100 — " 



SCALE OF FEET 



too 50 100 200 



Fig. 1. — Map of an eight-acre tract, showing borings made and data obtained therefrom. 



soil must be drained by a relief system. However, even where the in- 

 terception system can be used, it often is the case that in large tracts 

 supplementary drains will be needed to remove the water from the 

 already saturated soil and to provide outlet for the large quantities 

 of water that must be applied to wash out the heavy accumulations of 

 alkali. 



DEPTH OF DRAINS. 



The tendency in the arid West has been toward increasing the 

 depth of drainage ; this has been true especially with regard to shale 

 lands. The distance through which capillarity takes place is one of 

 the important factors regulating the minimum. Water passing up- 



