Hydrologic modeling of the Estancia Basin, New Mexico

-A conceptual and numerical model (ESTAN97) representing the hydrologic conditions of the Estancia basin was developed based on the basin's geologic structure and available hydrologic data. Geographic information systems (GIS) techniques were used in preparing the model input files. The Estancia basin is a topo graphically closed basin in central New Mexico with an area of about 2400 mi 2· The general surface drainage and subsurface flow is toward the central part of the basin where water is discharged by evaporation from a sys tem of playas and springs. ESTAN97 was calibrated to produce predevelopment (before 1940) and historical (1940-1996) water levels and flow conditions. Water budget analysis indicated that for the period from 1940 to 1996 about 2.08 million acre-ft of water was depleted from the basin during development. About 63% of this depletion came from aquifer storage, 34% came from salvaged evaporation and 3% was captured from neigh boring basins. The historical development has resulted in water-level declines of about 60 ft at the main pump ing centers and the disruption of the Antelope and Estancia springs. Population projections were used to esti mate future growth in domestic and public water-supply uses. Future irrigation use was assumed to decrease by 5% from 1996 uses. The results indicated that aquifer storage would maintain future development for at least 40 more years. It is expected that water levels at the main pumping centers will drop an additional 60 ft by the year 2036.