A Patchwork Quilt of Groundwater Depletion in the Eastern Great Basin, Nevada and Utah, USA

Located within the Basin and Range Physiographic Province, the Great Basin Carbonate and Alluvial Aquifer System covers 285,000 km², including 165 basins in eastern Nevada and western Utah. Between the 1940s and 1970s, groundwater withdrawals for irrigation in the region rapidly increased with the widespread use of the turbine pump. Since the 1970s, more efficient irrigation techniques and wetter-than-normal precipitation patterns have led to a reduction in well withdrawals for agriculture. Recent population growth (Las Vegas, Wasatch Front) and mining, however, have caused an increase in municipal and industrial withdrawals in some locations. The region’s high per capita water use and its arid setting have levied intensive demand upon existing groundwater resources. Competing demands on groundwater include municipal supply, agriculture, and springflow to support desert ecosystems. Recent (2000) annual total well withdrawals for the region were estimated to be about 1.5 million acre-feet.
Currently, substantial groundwater depletion only occurs in a few areas.  Cumulative groundwater depletion between 1940 and 2000 from just three southwestern Utah basins (Escalante, Milford, Pahvant) was about 5 km³, with related land subsidence and decrease in groundwater evapotranspiration. Long-term water-level hydrographs from 14 basins show groundwater level declines exceeding 50 ft; some basins have declines up to 200 ft. Recent (2000) well withdrawals approach or exceed estimated pre-development groundwater discharge in many other basins, indicating the potential for groundwater depletion. Las Vegas also has plans to pump up to170,000 acre-ft/yr from 6 lesser-developed basins in eastern Nevada, raising the possibility of additional groundwater storage loss. Based on further population growth and the prospect of future reductions in natural recharge associated with climate change (warmer winters with less snowpack), this trend of increasing groundwater depletion is likely to continue for many decades.