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The Snake River Plain Regional Aquifer System is collection of basalt and unconsolidated sediment groundwater aquifers underlying the Snake River Plain in the southern part of the U.S. state of Idaho extending into far eastern Oregon. Salmon Falls Creek. A discrete change in geologic conditions allows the Snake River Plain Regional Aquifer System to be commonly separated into two distinct parts, the Eastern Snake River Plain Aquifer and Western Snake River Plain Aquifer. The eastern portion of the aquifer is a significant source of irrigation water for the area's agricultural economy as well as being the sole source of water for over 300,000 people.

History
Surface water irrigation began along the Snake River Plain as early as 1843 with withdrawals from the Boise River. Development of the West around the 1900's, spurred on by the federal government, led to a large expansion of surface irrigation facilities. By 1929, 2.2 million acres of land were under surface water irrigation. This expansion of land under irrigation led to increased groundwater infiltration. From 1900 to 1950, groundwater levels increased at a volumetric rate of 0.838 km3 per year. Beginning in 1946, groundwater pumping became a source of irrigation water resulting in 700,000 acres being under groundwater irrigation by 1966. Since then, groundwater pumping has held fairly steady with only small expansions.

The expansion of groundwater in the 1950s and 1960s led to a reversal in groundwater infiltration with groundwater depletion volumetric rates of around .35 km3 per year from 1970 to 2008. In 2006, in response to the depletion of the aquifer, the Idaho Legislature passed a resolution calling for the creation of a comprehensive management plan for the Eastern Snake River Plain Aquifer. The plan was developed by the Idaho Water Resources Board in collaboration with many stakeholders from across the plain. It aims is to stabilize water withdrawals by shifting some users from groundwater to surface water, implementing aquifer recharge projects and demand reduction programs.

Eastern Snake River Plain Aquifer
The Eastern Snake River Plain Aquifer north of the Snake River is a remarkable aquifer of great resource and economic significance. It is not a single homogeneous geologic formation. Rather it consists of a volcanic pile of the Quaternary Snake River Group basalts. In eastern Idaho, these basalts may be about 1 mile thick. The individual flows are 20 to 30 feet thick with the upper 3 to 6 feet consisting of a very permeable rubble zone. Interbedded alluvial sediments are also found between many of the flows.

In the eastern Snake River Plain, the Snake River lies near the southern edge of the plain, about 40 to 50 miles southeast of the ranges of central Idaho. The rivers in the ranges north of the plain all disappear into the surface of the Snake River Plain near the mountain front. The Little Lost River is a typical example. For about 100 miles downstream from Milner Dam in the vicinity of Twin Falls an estimated total volume of approximately 200 billion cubic feet of water (1.4 cubic miles) enter the Snake River from gigantic springs on the north side of the canyon. This is the well-known Thousand Springs area.

Groundwater flows to the southwest through the Snake River Plains aquifer which is consistent with the overall tilt to the southwest of the basalt strata. The channel of the Snake River cuts through the aquifer. Consequently, the gravity and weight of the water in the basalt layers north of the river drives the huge springs.