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Show XII-50 UPDATING THE HOOVER DAM DOCUMENTS New Mexico, Utah, Arizona). The outflow point and drainage area for each is shown in table C-1. The boundaries of the reporting areas are shown on the frontispiece map. The largest consumptive use of water in the Upper Colorado River Basin results from the irrigation of about 1.5 million acres of pasture and harvested cropland. In the Upper Basin, there is little opportunity for measuring irrigation consumptive use directly by inflow-outflow methods. Therefore it was necessary to determine this use empirically. Specifically, irrigation consumptive use rates were computed from recorded climate data for each of the reporting years and applied against the best estimates of irrigation acreage. The modified Blaney-Criddle consumptive use quotation was selected for use in the Upper Basin. Irrigated acreage is the most important variable in the determination of irrigation consumptive use. Therefore, most of the data collection effort of this study was devoted to determining this item. It was also necessary to compute reservoir evaporation losses empirically, by developing equations of net evaporation rates for each of the reporting years and applying these rates against the best estimates of reservoir surface area. For the Upper Basin portion of this study, evaporation losses are reported under the item of use most closely associated with the principal reservoir function. Export of water out of the Colorado River system accounts for nearly one-quarter of the total uses and losses in the Upper Basin. For the purpose of this report, water exported across the basin divide was treated as an immediate loss to the river system. The values reported for the Upper Basin are composed of flows recorded at the diversion facilities and evaporation from reservoirs associated with export. TABLE C-1-Colorado River System Consumptive Uses and Losses, P.L. 90-537 Drainage Areas by States (and Mexico) and Major Tributary Streams Units= 1,000 Square Miles Major Tribute Strum, ami Tneir Selected Outflow Points Wyoming Colorado Utan Ntw Mexico Arizona Nevada California Mexico Total Green River at Colorado River Confluence, Utah 17.1 10.6 17.0 __ - - - - 44.8 Upper Main Stem at Green River Confluence, Utah - 22.2 4.0 __ - - - - 26.2 San Juan-Colorado at Lee Ferry, Arizona - 5.8 16.2 9.7 6.9 - - - 38.6 Little Colorado River near. Cameron, Arizona - - - 5.3 21.2 - - - 26.5 Virgin River at Little- field, Arizona - - 3.0 __ 1.9 0.2 - - 5.1 Muddy River near Glendale, Nevada - - - - - 6.8 - - 6..8 Bill Williams River below Alamo 0am, Arizona - - - - 4.7 - - - 4.7 Gila River below Painted Rock Dam, Arizona - __ - 5.6 44.2 - - (1.1) 49.8 Mainstream and Remaining Areas in Lower Basin - - 0.6 - 28.3 6.9 3.6 (0.1) 39.4 Colorado River System at Southerly International Boundary 17.1 38.6 40.9 20.6 107.2 13.9 3.6 (1.2) 241.9 Colorado River System above Lee Ferry 17.1 38.6 37.3 9.7 6.9 - - - 109.6 Colorado River System below Lee Ferry - - 3.6 10.9 100.3 13.9 3.6 (1.2) 132.3 |
