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Show PROBLEMS OF IMPERIAL VALLEY AXD VICINITY. the assumption that 85 pounds of dry matter is equivalent to a cubic foot of solid. Most of the time the Gila River is nearly dry and the little water it discharges is clear. The observations at Yuma, therefore, indicate the silt traveling at that time in the "Colorado above the Gila, and by difference at other times, the quantity discharged by the Gila during its relatively short high-water periods. Observations on the Gila have also been taken at Buttes above Florence and at San Carlos. A few observations have also been taken on the San Juan, the Green, and the Grand, but these are too few to be conclusive, and any statement concerning these streams must he considered as a very rough estimate. Th estimates on which this report is based: e following table shows the Table No. 4.-Silt content, main stream and tributaries. Annual water. Annual silt. Per cent silt. Colorado at Yuma Gila.........:.... San Juan......... Green............ Grand............ Other tributaries. Acre-feet. 17,740,000 j 1,070,000 I 2.700,000 ! 5,510,000 6,9*0,000 1, 560,000 Acre-feet. 113,000 15,000 29.000 30,000 20,000 19,000 0.65 1.40 1.07 0.54 0.29 1.22 The silt content of the Colorado, with the Gila not in flood, has averaged about 0.5 of 1 per cent, and this is fairly representative of the silt conditions at Boulder Canyon reservoir. The discharge at Boulder Canyon is estimated at 17,500,000 acre-feet annually. On this basis the average annual silt discharge is about 88,000 acre-feet per annum. POWER, POSSIBILITIES. The development of the best reservoir sites on the main branches of the Colorado River, if used for irrigation in the lower basin, would affect the conditions of power development in their basins below, because the water would be regulated in accordance with the needs of irrigation rather than of power. The power possibilities which would be affected thereby are shown in the following table, which is expressed in horsepower, continuous output, 88 per cent efficiency at the turbines. Table No. 5.-Power possibilities. Present. After irrigation develops above. Green River Basin: Yampa, below Juniper Reservoir............ White, below Rangely Reservoir............ Main stem, below Flaming Gorge Reservoir. Total, Green River Basin................. Grand River Basin, below Dewey Reservoir___ Colorado, exclusive of Grand Canyon Park..... 289,000 24,000 1,080,000 244,000 16,000 729,001) 1,393,000 210,000 4,410,000 989,000 210,000 3, 2(50,000 Total........... In round figures. 6,013,000 (3,000,000 3, 159,000 3, 400.000 The above power developments would be further diminished by evaporation from the reservoirs built for power which would depend largely upon the plan of development. |
