Hydrology and simulation of ground-water flow in southern Utah and Goshen Valleys, Utah

The ground-water resources of southern Utah and Goshen Valleys were assessed from 1988 to 1993 to determine the effects that additional ground-water withdrawals would have on water levels, surface water, and water quality. Recharge, movement, and discharge of ground-water were emphasized. The main ground-water system in southern Utah and Goshen Valleys is in the unconsolidated basin-fill deposits. Recharge to the ground-water system from streams, canals, irrigation, precipitation, intermittent and ephemeral runoff, and subsurface inflow was estimated to be 120,000 acre-feet in southern Utah Valley and 30,000 acre-feet in Goshen Valley in 1990. Discharge from the ground-water system to springs and drains, by evapotranspiration, to wells, streams, canals, Utah Lake, and sewer systems was estimated to be 130,000 acre-feet in southern Utah Valley and 33,000 acre-feet in Goshen Valley in 1990. Release from storage from March 1990 to March 1991 was estimated to be 9,800 acre-feet in southern Utah Valley and 3,400 acre-feet in Goshen Valley. Observed water-level fluctuations indicate that irrigation is not a major source of recharge in either valley and that precipitation is not a major source in Goshen Valley. In southern Utah Valley, water levels in March 1991 were not significantly different from water levels in March 1965. In Goshen Valley, water levels in March 1991 were higher than water levels in March 1965. A three-dimensional, finite-difference, ground-water flow model was used to simulate the ground-water system in the unconsolidated basin-fill deposits of southern Utah and Goshen Valleys. The steady-state conditions of 1949 and annual transient-state conditions from 1949 to 1990 were used to calibrate the model. Model-computed water-level declines of less than 20 feet are projected if municipal well withdrawals increase by 10,000 acre-feet per year. Model-computed water-level declines of 20 feet in southern Utah Valley and 40 to 80 feet in Goshen Valley are projected if well withdrawal is increased by 200 percent of the 1990 withdrawals.