Amounts of water withdrawn and consumptively used for irrigation
and other uses on the Snake River Plain were estimated to help deter-
mine hydrologic effects of ground- and surface-water use. Irrigation is
the largest off stream use of water on the plain. Surface-water irriga-
tion began in the 1840's and increased rapidly through the early 1900's.
Use of ground water for irrigation accelerated after World War II. In
1980, about 3.1 million acres were irrigated: 1.0 million acres were
irrigated with about 2.3 million acre-feet of ground water; 2.0 million
acres were irrigated with about 12.7 million acre-feet of surface water;
0.1 million acres were irrigated with combined surface and ground water.
Historical changes in aquifer storage and spring discharge are closely
related to changes in irrigation practices.
Industries, including aquaculture, withdrew an estimated 1.97 million
acre-feet of water. Withdrawals for other offstream uses, including public
and rural supplies, totaled 132,000 acre-feet. Hydroelectric power
generation is an economically important instream use of water. In
1980, about 52 million acre-feet of surface water was used to generate
2.6 million megawatt-hours of electricity. Native vegetation evapo-
transpired an estimated 3.7 million acre-feet, and 900,000 acre-feet
evaporated from bare ground and open water.
