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(Table 1.1). Approximately 95 million acre-feet of water is provided <br />annually to the upper basin through precipitation. All but about 15 <br />million acre-feet is lost to evapotranspiration; a part of the natural <br />hydrologic cycle. Of the surface flow in the upper basin, about 3.82 <br />million acre-feet is used by man. Irrigation, transmountain exports, <br />reservoir evaporation and other uses (municipal, industrial, power <br />generation, mineral extraction, livestock and stock-pond evaporation) <br />account for 56, 19, 19 and 6 percent, respectively, of the total con- <br />sumptive uses. The basin outflow (depleted flow) was nearly 11.3 <br />million acre-feet in 1975. <br />Table 1.1 Water Budget for the Upper Colorado River Basin, 1975 <br />(Figures computed from U.S. Water Resources Council, 1976) <br />acre-feet <br />Evapotranspiration . . . . . . . . . . 79,887,800 <br />Basin Outflow . . . . . . . . . . . . 11,288,300 <br />Irrigation Uses . . . . . . . . . . . 2,156,600 <br />Transmountain Exports . . . . . . . . 711,000 <br />Reservoir Evaporation . . . . . . . . 741,200 <br />Other Uses . . . . . . . . . . . . . . 215,100 <br />Total . . . . . . . . . . . . . 95, 000, 000 <br />Irrigation Use <br />The consumptive use of irrigation water is that volume lost to <br />soil evaporation and plant uptake and evapotranspiration. Incidental <br />loss also occurs such as evaporation from canals and associated re- <br />servoirs. Much of the water used for irrigation returns to the river <br />through surface and groundwater flow and is not considered consumed <br />or lost but is generally considerably altered in quality. <br />Irrigation and associated water use during 1975 accounted for <br />about 56 percent of the total depletion of water in the upper basin. <br />About 1.6 million acres of land are presently under irrigation, with <br />11