Hydrologic evaluation of Ashley Valley, northern Uinta basin area, Utah

Abstract

The water resources of the northern Uinta Basin, Utah and Colorado, were studied during 1971-74. Ashley Valley was evaluated in slightly greater detail than the general area, in order to assess the general relation of ground- and surface-water supplies. In Ashley Valley , the principal source of both irrigation supply and ground-water recharge is the flow from Ashley Creek canyon . Ground-water recharge to the valley fill, however, is mainly from canal and field losses along the west side of the valley. The permeability of the fill in most places is high, and water-level records indicate rapid changes in storage in response to the annual applications of irrigation water. Prior to the distribution of water from Steinaker Reservoir, the short runoff season led to a brief, intense irrigation period that was followed by a long period of post-irrigation drainage. After the reservoir began operation, smaller applications of water were made during a longer season, and ground-water levels rose in parts of the valley , mainly the lower areas. Despite local water-level rises, no perennially gaining reaches of the canals were observed. The amount of ground water available from storage in Ashley Valley is estimated to be 50,000-75,000 acre-feet (62-92 cubic hectometres), or enough water to supply irrigation in the valley for a maximum of 2 years. The ground-water storage varies annually about 10 percent and has not changed significantly. Ground water is discharged from Ashley Valley both by seepage back to Ashley Creek and by evapotranspiration . Evapotranspiration of surface and ground water has increased by an estimate 20 percent above the 48,000 acre-feet (59 cubic hectometers) determined for pre-reservoir conditions. As a result, the water that flows from Ashley Valley has been degraded in chemical quality. The water from Ashley Creek canyon is fresh . Mixing of snowmelt and base flow in Steinaker Reservoir yields a water of more uniform quality; but despite some concentration by evaporation from the reservoir, the outflow from the reservoir is fresh. Ground water in most of the valley is fresh , but the water increases in dissolved-solids concentration toward the south and east as a result of both evapotranspiration and solution of minerals from the valley fill and soils .