Summary of Ground-Water Conditions in Southern Arizona

Document: Summary of Ground-Water Conditions in Southern Arizona, June 1963, page 1Summary of Ground-Water Conditions in Southern Arizona Approximately 80 percent of the population and over 90 percent of the irrigated acreage in Arizona are concentrated in the alluvial basins of the southern part of the state. These basins are the major source of ground-water supplies in the state. In general, the basins have similar geohydrologic characteristics, although in detail each basin is different. An understanding of the pumpage, the level of the water table, storage capacity, recharge, permeability of the subsurface sediments, and methods of proper development and management is basic to the general solution of the water problems in these areas. The alluvial basins receive an average of about 10 inches of precipitation each year but only about 0.1 of an inch eventually reaches the water table. Most of the natural recharge to the ground-water reservoir occurs from streamflow instead of directly from rainfall. Nearly all the precipitation is eventually returned to the atmosphere by evapotranspiration. For the last several years ground-water pumpage from the alluvial basins has been nearly 4,500,000 acre-feet per year, of which about 250,000 acre-feet enters the reservoirs as natural recharge. The ground-water reservoirs in the alluvial basins may have had as much as 700,000,000 acre-feet of water in storage in the first 1,000 feet of saturated material, of which 80,000,000 acre-feet have been depleted to date. At the present annual pumping rate, this stored water would last well over 100 years if it were possible to withdraw it all and it was suitable for use. Part of this stored water will never be available to wells, and part will not be used because of undesirable quality and high temperature. Increased pumping lifts, lower yields of wells,Epson Perfection 4870 Photo, 400 dpi, 8 bit, 2,483,290 byte