IRRIGATION REQUIREMENTS OF THE GREAT BASIN 3 
termines the proper amount of water to be delivered to their respec- 
tive water users. 
A study of the duty of water on western lands was begun by the 
Division of Agricultural Engineering, 2 Bureau of Public Koacls, 
United States Department of Agriculture more than 25 years ago 
in an effort to solve the many-sided problem of what constitutes an 
adequate water supply for the irrigation of the standard crops and 
the modifications necessary on account of the prevailing types of soils 
and climatic conditions. Since then more or less experimentation 
along this line has been carried on by the department, chiefly in co- 
operation with western experiment stations. The results of the 
earlier experiments were published mostly in State and Federal bulle- 
tins which are now not easily procured. The results of later coopera- 
tive experiments, as a rule, have not been published. 
The present is an opportune time to collect all the reliable records 
available pertaining to this subject and to publish the summarized 
data so collected. With this end in view the arid and semi arid 
regions have been divided into five subdivisions in accordance with 
river basins rather than political boundaries. The information in 
this report deals with the Great Basin. 
UNITS AND FORMS OF EXPRESSION 
Since irrigation was first practiced in this country various units 
and forms of expression have been used to indicate the quantity of 
water required to irrigate an acre or other unit of land. Those in 
most common use are defined below, with some of their equivalents. 
The miner's inch represents, according to locality, the volume of 
water which will flow through an inch-square orifice under a con- 
stant head of 4 to 6 or more inches when measured from the 
surface of the water to the center of the opening. In southern 
California, Idaho, Kansas,, New Mexico, Xorth Dakota, South Da- 
kota, Nebraska, and Utah 50 miner's inches equal 1 cubic foot per 
second; in Arizona, Nevada, Montana, Oregon, and central Cali- 
fornia, 40 miner's inches, and in Colorado 38.4 miner's inches have 
that equivalent. 
An acre-foot of water is the quantity of water which will cover 
an acre to a uniform depth of 1 foot. It is equivalent to 43,560 
cubic feet. An acre-inch is one-twelfth of an acre-foot. 
Duty of water, as defined by Sir Hanbury Brown, 3 is " the measure 
of the efficient irrigation work that water can perform, expressed in 
terms establishing the relation between the area of crop brought to 
maturity and the quantity of water used in its irrigation." The 
duty of water is usually expressed in acre- feet per acre or in the 
number of acres irrigable by 1 cubic foot per second. Intake or 
gross duty is the average duty under a canal system when all trans- 
mission losses are included. Delivered or net duty is the duty at 
the margin of fields when all transmission losses are deducted. 
2 The irrigation work of the United States Department of Agriculture was originally 
conducted under the supervision of the Office of Experiment Stations and designated as 
" Irrigation Investigations." Later, under a reorganization of the department, this and 
other agri cultural engineering activities were grouped in a division of agricultural engi- 
neering and made a part of the Bureau of Puhlic Roads., 
3 Irrigation, Its Principles and Practice, as a Branch of Engineering, by Sir Hanbury 
Brown, London, 1920, 3d edition, p. 32. 
