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Hydrology of the Oakley Fan Area, south-central Idaho

Water-Resources Investigations Report 88-4065

Prepared in cooperation with Southwest Irrigation District
By:
,

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Abstract

The Oakley Fan area is a broad, crescent-shaped lowland along the southern margin of the Snake River Plain in south-central Idaho. Intensive groundwater development for irrigation has resulted in rapid water-level declines and, as a consequence, designation by the State of four Critical Groundwater Areas. Principal aquifers are in limestone, rhyolite, basalt, and alluvium. Annual water-level declines range from 3 ft to about 5 ft. Recharge to the groundwater system is from infiltration of surface water used for irrigation, precipitation on the surrounding mountains, infiltration of localized runoff, and upward movement of thermal water. Groundwater pumpage during the period 1979-84 averaged 173,000 acre-ft/yr. Surface and groundwater is predominantly a calcium bicarbonate type with variable concentrations of dissolved solids. Comparisons of silica and chloride concentrations and isotopic composition of groundwater were useful in determining areal extent of aquifers and movement of groundwater. A three-dimensional mathematical model of the Oakley Fan area was developed. The aquifer system was simulated in three phases: (1) Average 1979-84 hydrologic conditions, (2) 1910 hydrologic conditions, and (3) 1910-84 hydrologic conditions. Model simulation indicated that, for the period 1945-79, subsurface outflow declined from 327,000 acre-ft/yr to 215,000 acre-ft/yr. Simulated groundwater pumpage during the period 1945-79 was 3,000,000 acre-ft; simulated change in storage was 250,000 acre-ft. Simulations with the model approximate natural conditions and probably can be used to evaluate future changes in the hydrologic system.

Geospatial Extents

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Hydrology of the Oakley Fan Area, south-central Idaho
Series title:
Water-Resources Investigations Report
Series number:
88-4065
Year Published:
1989
Language:
English
Publisher:
U.S. Geological Survey
Contributing office(s):
Idaho Water Science Center
Description:
Report: v, 73 p.; 4 Plates: 31.50 x 36.38 and smaller
Number of Pages:
80
Country:
United States
State:
Idaho
Other Geospatial:
Oakley Fan Area
Scale:
250000