Appraisal Report Central Arizona Project

Document: "Appraisal Report Central Arizona Project-Chapter III", January 1962, page 31Service Zone, the ground-water reservoir provides both short-and long-term regulation of surface flows. On a short-term basis, winter and summer stormflows which occur beyond the capacity for direct diversion escape past the dams, and that portion not lost to evaporation and phreatophytes percolates to the underground reservoir. It is this type of operation which is the basis for the statement that substantially all of the surface inflow to the area is presently being used, as there has been essentially no escape from the basin since 1941. It is in the long-term storage function of the ground-water reservoir wherein lie the water problems of the area. The annual use of ground water is far greater than the annual recharge, and has been for many years. In terms of the quantities involved during the past 5 years, water requirements are estimated to have averaged about 4,490,000 acre-feet annually. Comparison of this present requirement with the average annual long-term surface supply of 1,020,000, as shown in table 3, indicates that ground-water reservoir must have supplied the difference, or 3,470,000 acre-feet annually. Ground-water annual safe yield, expressed as gross pumpage, has been estimated to be about 1,510,000 acre-feet, or 1,280,000 acre-feet after appropriate allowance for conveyance losses. Thus, the average annual water supply deficiency, on the basis of long-term ground-water and surface-water yields, is estimated at about 2,190,000 acre-feet. The net result has been a general overdraft on the ground-water reservoir and a constant lowering of ground-water levels. This overdraft has enabled an agricultural economy to continue, although on a changing economic basis. Irrigated acreage of the lower payment capacity crops is going out of 31Epson Perfection 4870 Photo, 400 dpi, 8 bit, 1,043,652 byte