Groundwater Depletion in the Alluvial Basins of Arizona – Tools to Analyze and Present Information On Water-Level Declines

Arizona is located in an arid to semi-arid region in the southwestern United States and is one of the fastest growing states in the country.  Population in Arizona surpassed 6.5 million people in 2008, an increase of 140 percent since 1980.  The alluvial basins of Arizona are part of the Basin and Range Physiographic province and cover nearly 74,000 square miles, 65 percent of the state’s total land area, include over 85 percent of the state’s population, and account for over 95 percent of the state’s groundwater use.  To provide updated information to stakeholders concerned with issues pertaining to limited groundwater supplies and projected increases in groundwater use, the USGS Groundwater Resources Program instituted the Southwest Alluvial Basins (SWAB) Groundwater Availability and Use Pilot Program.  As part of this program, methods and indicators were developed for assessment and presentation of regional groundwater conditions in the alluvial basins of Arizona using existing information in groundwater databases.  Computer programs were written to compute maximum water-level declines in the data, create annotated water-level hydrographs, and create input files for displaying well locations and linked hydrographs in an interactive geographic information system (GIS) format.  Results indicate that water-level declines of at least 75 feet were recorded in more than 1,900 wells in the most developed basins of the study area.  Maximum observed declines were as much as 500 feet.  Observations in over 40 percent of the wells with at least 75 feet of decline indicated continued water-level decline after 1997.  The majority of the most-severe water-level declines are seen in areas of the state with a history of heavy groundwater pumping for agriculture.  These and other indicators of groundwater conditions in Arizona are illustrated in an online interactive map (http://montezuma.wr.usgs.gov/website/azgwconditions).