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Outcropping limestone in Great Basin National Park.




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Great Basin Carbonate-Alluvial Aquifer System (GBCAAS) Water Availability

Project Chief: Victor Heilweil, USGS Salt Lake City, Utah
Cooperators: USGS California Water Science Center, USGS GD-Denver
Period of Project: 2007-present

Base Map (Click map for a larger view)

Base Map (Click map for a larger view)


The objective of the USGS Water Availability Program is to assess water availability in the Nationís major aquifer systems. The Great Basin Carbonate and Alluvial Aquifer System (GBCAAS) is part of this federally funded program. Specific objectives of this study include quantifying current ground-water resources, evaluating how those resources have changed over time, and developing tools to assess system responses to stresses from future human uses and climate variability.

Description of the Study Area

The GBCAAS study covers an area of more than 100,000 mi2 encompassing most of the Great Basin regional aquifer system. The area is characterized by numerous arid to semi-arid basins with unconsolidated alluvial aquifers separated by mountain ranges often comprised of carbonate aquifers. Population is concentrated within 100 miles of Salt Lake City and in the Las Vegas area and is growing rapidly. In the less populated areas, ranching and irrigated farming are the main economies. The area includes two national parks and numerous national wildlife refuges.


This study will compile and interpret pertinent information related to the regionís geology and hydrology to develop a conceptual understanding of water movement within the system and then use the knowledge to construct a numerical model for better understanding the current system response to natural and human stresses. This tool will also be used to forecast how the system might respond to future climate variability and water use.

Timeline and Products

This was a five-year (2007-2011) study of groundwater availability in the Great Basin Regional Aquifer System. The primary study objectives were (1) to compile and interpret hydrogeologic information to develop an updated conceptual model of the aquifer system; and (2) to develop a numerical groundwater flow model for testing the conceptual model, and for providing additional insight on groundwater quantities and flow directions. The conceptual model includes the delineation of hydrogeologic units based on geology and hydraulic properties, construction of a detailed three-dimensional hydrogeologic framework, development of a potentiometric-surface map of the aquifer system, an evaluation of interbasin hydraulic connectivity and regional groundwater flow directions, and a synthesis/interpretation of both pre-development and recent groundwater recharge and discharge budget components. Data compiled for this study generally includes information from 1940 through 2006, as data prior to the 1940s are scarce. The conceptual model is documented in U.S. Geological Survey Scientific Investigations Report 2010-5193, entitled “Conceptual Model of the Great Basin Carbonate and Alluvial Aquifer System”. The numerical groundwater flow model has been constructed and is currently being calibrated to steady-state conditions. A Scientific Investigations Report describing the numerical model is planned for publication in 2014.

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