NEW GROUND-WATER BUDGET ESTIMATES FOR THE EASTERN GREAT BASIN

The Great Basin Carbonate Aquifer Province occupies an area of 285,000 square kilometers and includes 165 separate basins, predominantly in eastern Nevada and western Utah, USA. While most ground-water use is from basin-fill aquifers, an integrated fabric of underlying and connected carbonate and volcanic rock aquifers provide recharge to these basins and often act as conduits for interbasin flow. During the last decade, portions of this region had some of the highest rates of both population growth and per capita water use in the United States. The combination of rapid growth and arid setting have levied intensive demand upon existing ground-water resources. As part of the U.S. National Water Census, a four-year water availability study is currently underway to evaluate ground-water resources of the eastern Great Basin. This study is providing an updated characterization of the regional ground-water flow system including a three-dimensional hydrogeologic framework of the aquifer system, a detailed water-budget analysis, and the development of quantitative numerical modeling tools to assess ground-water system responses to human and climatic stresses.

As part of the detailed ground-water budget analysis, data from over 100 individual reports were compiled, evaluated, and re-interpreted for the 165 individual basins. New ground-water recharge estimates from a GIS based recharge-runoff model (Basin Characterization Model) were also developed at a 270 meter grid scale for the study area. Previously reported ground-water recharge estimates for the eastern Great Basin study area range from 3,200,000 to 5,500,000 acre-ft. The current study estimate of pre-development (pre-1940) ground-water recharge falls within this range, and includes recharge from infiltration of precipitation, infiltration from surface water sources, and subsurface ground-water inflow. Previously reported estimates of annual ground-water discharge range between 3,400,000 and 4,100,000 acre-ft. The current study estimates of pre-development ground-water discharge is similar to the higher end of this range, and includes ground-water discharge to evapotranspiration, springs, mountain and basin-fill streams/lakes/reservoirs, and subsurface ground-water outflow.