HYDROGEOLOGIC EVIDENCE FOR GROUND-WATER DISCHARGE FROM THE REGIONAL CARBONATE-ROCK AQUIFER SYSTEM TO THE COLORADO RIVER, SOUTHEASTERN NEVADA

A vast regional Paleozoic carbonate–rock aquifer system has been identified in the Great Basin region in Nevada and adjacent States, which extends from the Great Salt Lake on the northeast to Death Valley on the southwest. Major ground-water flow systems identified within the carbonate-rock aquifer system include the Great Salt Lake system in the northeast, the Death Valley system in the southwest, and the Colorado system in the southeast.

Recharge to the carbonate-rock aquifer system occurs principally in mountainous areas in east-central Nevada. Ground-water moves in fractures and enhanced solutioned openings, principally northeastward and southward from this area of principal recharge. Discharge occurs principally to large-volume springs, to evapotranspiration, to base-flow to streams in places, and perhaps to regional ground-water flow directly to the regional sinks at the Great Salt Lake, Death Valley salt pan, and Lake Mead on the Colorado River.

The water balance for the lower Colorado ground-water flow system has been the subject of scrutiny in recent years, due to efforts to ensure sustainable ground-water development in the regional carbonate-rock aquifer northeast of Las Vegas in response to rapid population growth in the area. Empirical methods have been used to estimate the distribution of ground-water recharge within the regional ground-water flow system, by apportioning measured regional ground-water discharge. Recently, revised empirical methods have been used to estimate regional ground-water recharge from newer estimates of precipitation and evapotranspiration. Then, undiscovered regional discharge has been estimated based on the difference between these new, larger recharge estimates and measured discharge.