USGS Report Indicates Groundwater Withdrawals Outpacing Aquifer Recharges in Arizona

Study also includes new groundwater-flow model to evaluate interconnected groundwater basins

U.S. Geological Survey scientists released a report yesterday evaluating groundwater availability and use for all of Arizona’s alluvial basins from 1940-2007. The report finds that groundwater in the basins was depleted by more than 74.5 million acre-feet, or approximately three times the maximum storage of Lake Powell. 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% of the state’s groundwater use, with groundwater providing about 43% 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[s] are balanced with Arizona's agricultural sector," said USGS hydrologist Fred Tillman, who led the 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 study 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 Arizona Groundwater Conditions Interactive Map.

The pilot study also demonstrates 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.

U.S. Geological Survey

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