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Geohydrology and simulation of ground-water flow in the Mesilla Basin, Dona Ana County, New Mexico, and El Paso County, Texas

1990; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr88305

2332-4899

Peter Frenzel, Charles A. Kaehler, Scott K. Anderholm,

Hydrology and Watershed Management Studies

The ground-water hydrology and geochemistry of the Mesilla Basin in central-southern New Mexico and western Texas were studied as part of the Southwest Alluvial Basins Regional Aquifer-System Analysis program of the U.S. Geological Survey.The Mesilla Basin, hydrologically representative of many alluvial basins, was studied by simulating the ground-water flow system using a digital model.The basin fill, composed of Santa Fe Group and younger deposits, forms a three-dimensional ground-water flow system whose lateral extent and depth are defined by bedrock with much smaller hydraulic conductivity than the basin fill.Ground-water flow generally is away from the Mesilla Valley near Las Cruces and toward the valley in the southern part of the basin.Most flow into and out of the ground-water system occurs at or near land surface in the Mesilla Valley and is the result of interaction of the Rio Grande, drains, canals, evapotranspiration, and ground-water withdrawals.These flows fluctuate in the short and intermediate term (to as much as about 5 years) with the availability of surface water, but in the long term they do not change much.The general direction of ground-water flow is southeastward along the Mesilla Valley.Some recharge results from torrential surface runoff, mainly near mountain fronts.Recharge over most of the West Mesa area is unlikely, but occasionally may occur in places. 1The chemical composition of ground water in the Mesilla Valley varies areally and vertically.The large variation is due to mixing of excess applied irrigation water and ground water.The location of the transition zone between these two water types probably moves in response to ground-water pumpage.Some ground water enters the basin fill from bedrock at depth.Along the northwestern margin of the basin, sulfate and sodium are the dominant ions in ground water flowing into the basin, and the specific conductance of this water ranges from 1,400 to 2,310 microsiemens per centimeter at 25 degrees Celsius.Ground-water inflow along the southwestern margin of the basin consists of two types: bicarbonate and sodium are the dominant ions in one type, and chloride and sodium are the dominant ions in the other type.Inflowing geothermal water, which has large concentrations of chloride, silica, and potassium, mixes with cool, less mineralized water along the eastern side of the Mesilla Basin.Calculated chemical-geothermometer temperatures indicate that geothermal-reservoir temperatures may be as great as 230 degrees Celsius.