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Show CHAPTER D - PRESENT STATUS OF RESOURCE USE AND DEVELOPMENT WATER RESOURCES The Lower Colorado Region probably comes closer to using the last drop of available water for man's needs than any other area in the United States. These water supplies are also among the most regulated and metered in the Nation, Despite the most frugal use, recycling, and the highly efficient regulation of water, the Region is mining water each year that cannot be replenished by natural recharge for many decades. Virtually every sector of the Region's socio-economic struc- ture is being sustained in some degree by the overdraft of ground water. Three main sources of water were available in 19&5 f°r use * Lower Colorado Region: (a) Entitlement to 3.1 million acre-feet of Colorado River water by a body of law referred to as the "Law of the River;1' (b) Local runoff amounting to 3.12 million acre-feet originating within the regional boundaries; and (c) Local ground-water reserves. The 3.1 million acre-feet entitlement from the Colorado River has not been fully utilized because of the lack of conveyance facilities to transport water to the areas of heavy demand. About 8.2 million acre- feet were withdrawn from surface- and ground-water sources in 19&5 • Approximately 5 million acre-feet, about 60 percent, of this was from ground-water reserves of which an estimated 2,5 million acre-feet were in excess of the annual replenishment. The area of greatest use of water for municipal, industrial and irrigation purposes was the Phoenix-Tucson area of Arizona where most of the Region's ground-water overdraft occurred. Las Vegas Valley, Nevada, lacking facilities for diversion of adequate quantities of Colorado River water, was also pumping from ground-water reserves in 1965. Figure k compares the amounts and proportionate parts of water withdrawn in 1965 from ground water and surface water. About 9k percent of the total regional water withdawal was for irri- gation, and 6 percent was for municipal, industrial, and all other uses. Only minor quantities are used for electric energy generation, mineral- production, fish and wildlife, and recreation. |