Hydrology of the Oakley Fan Area, south-central Idaho

Abstract

Surface and ground water is predominantly a calcium bicarbonate type with variable concentrations of dissolved solids. Comparisons of silica and chloride concentrations and isotopic composition of ground water were useful in determining areal extent of aquifers and movement of ground water. 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-feet per year to 215,000 acre-feet per year. Simulated groundwater pumpage during the period 1945-79 was 3,000,000 acre-feet; simulated change in storage was 250,000 acre-feet. Simulations with the model approximate natural conditions and probably can be used to evaluate future changes in the hydrologic system.