The problem of what constitutes an adequate water 
supply for irrigation of lands in the arid and semiarid 
regions is of vital importance to those regions. In an 
effort to solve this problem the Division of Agricultural 
Engineering, Bureau of Public Roads, of the United 
States Department of Agriculture, has been studying the 
duty of water for the past 25 years. A part of the 
results of the earlier experiments were published by 
State and Federal agencies, but the results of later coop- 
erative experiments, as a rule, have not been published. 
It now seems desirable to summarize and publish in 
bulletin form the data so collected. In order to treat the 
subject adequately, the arid and semiarid regions have 
been divided according to watersheds. This report 
relates to the Great Basin. 
The Great Basin comprises an area of about 138,789,000 
acres, of which 2,313,165 acres were irrigated in 1920. 
The crops grown include hay, grain, and potatoes at 
the higher altitudes, and alfalfa, grain, corn, fruit, and 
canning vegetables on the bulk of the arable lands at 
lower elevations. 
It is estimated that eventually an area of 5,000,000 
acres may be irrigated with the available water supply, 
or approximately double the area irrigated in 1920. 
This estimate is based on the assumption that water will 
be used much more economically than at present; that 
the supply will be regulated by means of storage reser- 
voirs; and that waste or return water will be reused 
wherever possible. The seasonal net water require- 
ment of crops under careful use is found to vary from 
1.5 acre-feet per acre to 2.2 acre-feet per acre, depend- 
ing on the locality. 
