Streamflow losses and changes in ground-water levels along the Salt and Gila Rivers near Phoenix, Arizona — February 1978 to June 1980

From March 1978 to June 1980, high runoff from the Salt and Verde drainage basins combined with large carryover storage in a reservoir system led to the release of about 8.26 million acre-feet of water. About 2.89 million acre-feet of the water was diverted above Granite Reef Dam, and about 5.45 million acre-feet was released into the normally dry channel of the Salt River. The total streamflow losses in the 74-mile reach between Granite Reef and Gillespie Dams were at least 474,000 acre-feet. Most of the water infiltrated into the permeable alluvial deposits along the Sal and Gila Rivers and increased the amount of ground water in storage. From February 1978 to May 1980, ground-water levels in 169 wells that tap the alluvial deposits in the Salt River Valley rose an average of 35.5 feet. The rise in ground-water levels was a direct result of the infiltrating floodwaters and a marked decrease in ground-water pumpage. (USGS)