INVESTIGATING GROUND-WATER MOVEMENT WITH AN EMBEDDED MODEL, AMARGOSA DESERT, NEVADA AND CALIFORNIA

Effects of ground-water pumping on springs and riparian habitat in the southern Amargosa Desert are being investigated with a local scale, embedded ground-water flow model. This local-scale model (500-m grid spacing) is a subset of and will be embedded into the U.S. Geological Survey's transient model of the Death Valley regional ground-water flow system (DVRFS) (1,500-m grid spacing). The local-scale model uses the local grid refinement (LGR) package in MODFLOW-2005 and updated (through 2003) pumping data. Calibration targets used for the local-scale model include updated water levels and spring flow data (through 2003).

An updated and more detailed hydrogeologic framework model (HFM) is being developed for a smaller area, about 3,300 square kilometers, within the DVRFS framework. This local-scale HFM uses borehole lithologic data, revised interpretations of geologic structure, and a reevaluation of existing geologic conceptual models. Gravity, ground-magnetic, and audiomagnetotelluric geophysical surveys were conducted to assess structure; geophysical models were calibrated to measured physical properties of hand samples, as well as available seismic and borehole data.

A preliminary east-west crustal model through Devils Hole and across the Amargosa Trough was developed using gravity measurements, well information, and geologic mapping. Cenozoic basin fill is represented in a 3D-lithology model of the Amargosa Desert built from borehole and geologic map data. The new HFM provides more detail in the heterogeneity of the basin fill, but presents challenges in merging this detailed representation with the more generalized one of basin-fill units within the DVRFS model. New geologic data and the more detailed local-scale HFM are being used to subdivide the regional units into hydraulic-conductivity zones based on the 3D distribution of lithologies.