DRAINAGE OF 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 sufliciently 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 
TESTAW CS fe Eas O Ground Surface -~—\06— 
Fe lowing Test Wells._@ Shale Surface ——|00—— 
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 apphed to wash out the heavy accumulations of 
alkali. 
DEPTH OF DRAINS. 
The tendency in the arid West has been toward increasing ‘thee 
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- 
