Hydrology of Salt Wells Creek : a plains stream in southwestern Wyoming

Development of energy minerals in plains areas of Wyoming is increasing rapidly. Such developments may affect water resources and hydrologic relations of the plains; however, little information exists concerning hydrologic processes of these areas. This report summarizes results of a hydrologic study made during 1975-78 of Salt Wells Creek, a stream typical of those in arid and semiarid plains areas in southwestern Wyoming where mineral development is occurring. Salt Wells Creek has a drainage area of about 500 square miles and is located southeast of Rock Springs, Wyoming. The creek drains into Bitter Creek, which is a tributary of the Green River. Numerous springs in the headwaters cause small perennial flows in some upstream tributaries. Evaporation, freezeup, and seepage deplete these flows so that the middle and lower reaches of the main channel have only intermittent flows as a result of snowmelt and rainfall runoff. The average annual runoff of the stream is estimated to be about 2,000 to 3,000 acre-feet, which is not a large amount in comparison to flows of major perennial streams of southwestern Wyoming. The intermittent nature of the streamflow has a significant effect on water quality. "Flushing" of accumulated salts and sediment occurs during the first flows following rainfall or snowmelt. This flushing follows dry periods when salts and loose sediment accumulate on the basin surface and in the stream channels. The first flows during runoff transport these materials as dissolved and suspended loads. After this initial flushing of the basin surface and channels, concentrations decrease. Ground water is significant to the area because numerous springs in the headwaters are used for stock and wildlife watering. Ground-water quality depends greatly upon the source aquifer. Dissolved-solids concentrations ranged from 70 to 2,400 milligrams per liter. At 12 of the 14 ground-water sites where samples were collected, dissolved-solids concentrations were less than 1,000 milligrams per liter. Calcium and magnesium generally are the dominant cations and sulfate and bicarbonate, the dominate anions. A striking feature of Salt Wells Creek and its major tributaries is their deeply incised channels. The incision is attributed to the cumulative effects of: (1) A change in the relative amounts of annual precipitation occurring as rain and snow, (2) a change in the base level of the streambed due to downstream channelization, and (3) changes in land use. Gullies are now expanding to include intervening tributaries, and an erosion problem exists. INTRODUCTION Located just southeast of Rock Springs, Wyo. , Salt Wells Creek is an intermittent stream that drains a 500 square-mile area comprised mainly of arid or semiarid plains; the drainage pattern is shown in figure 1. The stream heads in low-lying mountains near the Colorado-Wyoming State line and flows in a northerly direction into Bitter Creek, a stream that flows westerly through Rock Springs and eventually into the Green River. The hydrology of Salt Wells Creek is typical of that for other basins in the desolate, mineral-rich plains of southwestern Wyoming. An increasing amount of attention is being directed toward these areas due to their extensive coal, oil, gas, uranium, trona, and oilshale deposits. Large-scale developments of these deposits will require an understanding of the plains environment, including its hydrology. Prior to this study, few comprehensive investigations had been made and little knowledge existed about hydrology of plains areas in southwestern Wyoming (Lowham and others, 1976).