Page 4

The unmeasured net losses include nonbeneficial consumptive use by phreatophytes, channel evaporation, operational spills, unaccounted diversions, and unmeasured surface and subsurface inflows and outflows. Total annual unmeasured net channel losses are estimated to be 900,000 acre-feet between Hoover Dam and Mexico, of which 230,000 acre-feet are estimated to be operational spills at Imperial Dam. Lower Colorado River Tributary Areas Water Supply--The major tributaries to the Colorado River below Lee Ferry, Arizona, are the Little Colorado, Virgin, Bill Williams, and Gila Rivers. Other minor tributaries include Kanab, Bright Angel, and Havasu Creeks, and the Muddy River. Table 7 gives the average annual runoff of selected U. S. Geological Survey gaging stations for the 16-year period 1946-61, and the 1961 runoff. The early development of water supplies in the Lower Colorado River tributary areas was largely from surface-water supplies; however, due to technological advances and increased demands, usage of ground water now far exceeds surface water. With minor exceptions, a condition of moderate-to-severe overdraft is prevalent in every developed ground-water basin in the area. Present gross pumpage in Arizona is estimated to be about 4,900,000 acre-feet annually. About 2,400,000 acre-feet of this withdrawal is mined water--water that is not being replenished. Present gross pumpage in that portion of Nevada tributary to the Colorado River, essentially limited to the Las Vegas Basin, is estimated to be about 65,000 acre-feet annually, with about 30,000 acre-feet of this withdrawal being mined. Present gross pumpage in that portion of New Mexico tributary to the Colorado River, essentially limited to the Gila River Basin, is estimated to be about 25,000 acre-feet annually. It is indicated that there has been no long-term water level decline, although there may be localized deficiencies. No data are available to estimate the relatively minor quantity of gross pumpage in that part of Utah tributary to the Colorado River. A unique source of local supply is the desalting of poor quality water. In September 1962 the town of Buckeye, Arizona, put into operation the first saline water conversion plant to furnish the entire domestic water supply of a community. The plant uses the electrodialysis process, and is claimed to be the largest and lowest cost commercial plant of its type built, as of the date of its installation. It has a total capacity of 650,000 gallons of reclaimed water per day at present, and can be expanded to 750,000 gallons per day. Total dissolved solids are reduced from 2,100 p.p.m. to 500 p.p.m. III-4Epson Perfection 4870 Photo, 400 dpi, 8 bit, 14,141,440 byte