Hydrology and simulation of the ground-water flow system in Tooele Valley, Utah

Abstract

The study described in this report was conducted in cooperation with local, State, and Federal agencies to improve current understanding of the regional ground-water flow system in Tooele Valley. Available data were compiled and analyzed and then used to develop a conceptual model of the flow system. Recharge to the ground-water flow system is mainly from subsurface inflow from consolidated rock and stream-channel deposits, infiltration of precipitation on the valley floor, seepage from irrigated fields, and subsurface inflow from Rush Valley. Long-term average recharge for these sources is 48,000 acre-feet per year, 12,000 acrefeet per year, 10,000 acre-feet per year, and 5,000 acre-feet per year, respectively. Discharge from the ground-water flow system is mainly by pumped and flowing wells, evapotranspiration, springs, subsurface outflow to Great Salt Lake, and shallow drains and ditches. Long-term average discharge to these processes is 26,000 acre-feet per year, 23,000 acre-feet per year, 16,000 acre-feet per year, 3,000 acre-feet per year, and unknown, respectively.Numerical simulation of the ground-water flow system in Tooele Valley was used to test and refine the conceptual understanding. The numerical simulation was calibrated to match steady-state conditions in 1968 and transient-state conditions during 1969-94. Calibration was achieved by adjusting numerical parameters until a reasonable match between (1) model-computed and measured water levels, (2) model-computed and estimated discharge, and (3) model-computed and measured water-level fluctuation, was attained.Steady-state calibration resulted in a reasonable match between model-computed and measured water levels throughout most of Tooele Valley. The results of transient-state calibration indicate that the generally observed rising and declining trends in water levels at observation wells are reproduced in many areas of Tooele Valley. The model generally does not simulate the large and abrupt water-level changes from year to year in some areas of Tooele Valley.