New Mexico Geological Society Annual Spring Meeting — Abstracts

The Estancia Basin is a closed basin in central New Mexico with an area of about 2400 square miles. Precambrian rocks crop out in the higher part of the south Manzano Mountains, Lobo Hill and Pedemal Hills. The valley floor contains a series of salt playas and an accumulation of several hundred feet of unconsolidated valley fill. The principal aquifers in the Estancia Basin are Madera Limestone, Glorieta Sandstone and the Valley Fill. Prior to heavy pumping for irrigation, natural discharge was by evaporation from the playas, evapotranspiration from the springs and deep leakage to the north (Galisteo Basin). A conceptual and a numerical model for the Basin was constructed based on its geologic structure, test drilling at two sites and the available hydrologic data. The geographic information system (ArcView GIS) was combined with MODFLOW to generate the numerical model data files. The model was calibrated using manual and automatic (MODFLOWP) calibration processes. Sensitivity analysis indicated that the model is sensitive to the amount of the recharge of the Madera Limestone. The model was used to simulate the predevelopment and development conditions. Historical simulation indicated that the sources ofthe pumping development are 50 percent from storage and 50 percent from drying springs and salvaged evapotranspiration. The hydrologic model of the Estancia Basin provides an improved means of explaining historical conditions and projecting future conditions in the basin.