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New USGS Science for Managing Arizona’s Groundwater
Released: 9/21/2011 11:30:00 AM

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communications and Publishing
12201 Sunrise Valley Dr, MS 119
Reston, VA 20192
Fred D. Tillman 1-click interview
Phone: (520) 670-6671 ext. 223

James M.  Leenhouts 1-click interview
Phone: (520) 670-6671 ext. 278

Jessica K.  Robertson 1-click interview
Phone: (703) 648-6624

The report can be found online.

Over the last 70 years, groundwater in Arizona's alluvial basins was depleted by more than 74.5 million acre-feet, or approximately three times the maximum storage of Lake Powell. 

U.S. Geological Survey scientists recently released a report evaluating groundwater availability and use for all of Arizona's alluvial basins from 1940–2007. Arizona’s alluvial basins, located south of the Colorado Plateau, are aquifers composed of sand, silt and clay material that has eroded from mountains surrounding the basins. 

These alluvial basins account for 95 percent of the state’s groundwater use, with groundwater providing about 43 percent of the entire state’s water supply. 

"Arizona is one of the fastest growing states in the nation, and groundwater supplies will undergo increased demand as water needs for growing population are balanced with Arizona's agricultural sector," said USGS hydrologist Fred Tillman, who led this water availability and use pilot study. "This USGS report is intended to aid state and local agencies by providing them information about groundwater to help better plan for the future."

Groundwater withdrawals total about 2.4 million acre-feet per year in the study area, mainly for agriculture use and secondarily for municipal use. The primary source of groundwater recharge, or replenishment, comes from mountain runoff that flows into the groundwater basins. Groundwater in these basins has been depleted because the amount of withdrawal has outpaced aquifer recharge. 

The new report includes updated groundwater budget information for each of the 45 individual basins or management areas, as well as a new groundwater-flow model to test an approach for evaluating interconnected groundwater basins. Several indicators of groundwater conditions are also analyzed, building on previous work that resulted in the popular Arizona Groundwater Conditions Interactive Map

"The new USGS report on groundwater availability and use in Arizona is a valuable compilation of information and data," said Frank Corkhill, Chief Hydrologist of Arizona Department of Water Resources. "The report provides a significant analysis of recent water-level data and long-term trends and provides a well-balanced assessment of the strengths and weaknesses of various methods used to estimate groundwater budget components." 

The groundwater assessment and methods development effort piloted in Arizona's Southwest Alluvial Basins is being conducted by the USGS Groundwater Resources Program. Information derived from this study in collaboration with more than 30 regional aquifer studies, once completed, will provide a collective assessment of America's groundwater availability. 

This pilot study of Arizona's Alluvial Basins was an important step forward because the groundwater-flow model developed for several basins in southern Arizona demonstrated that it is possible to model the interconnected nature of adjoining basins and assess how changes to groundwater supplies in one area might affect flow to or from adjacent areas.

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