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,,;"''1i?O HU {.; 1_ demands. The outlet works will be designed to withdraw water from between elevations 4,920 and 4,950. G. Sedimentation There have been a few studies of sediment loadings within the White River Basin. Sediment measurements have not been made in the lower reaches of the White River prior to the 1975 water year. The U. S. Geological Survey began collecting sediment data on the White River at the mouth near Ouray in October 1974. This data has been published for the 1975 and 1976 water years. Long-term studies have been made in the upper reaches of the White River near Buford, Colorado. Suspended sediment discharge for this area averages approximately 33,000 tons or 22 acre-feet per year. This drainage area is approximately 424 square miles which results in about 78 tons per square mile or 0.05 acre-feet per square mile. This value is quite low, especially when compared to other drainages in the Colorado River Basin. A 20-year record of suspended sediment discharge of the Green River at Green River, Utah, before construction of Flaming Gorge Dam resulted in an average annual sediment load of 0.26 acre-feet per square mile of drainage area. The Dolores River drains an area south of the White River with approximately the same area. The Dolores River at Cisco, Utah, yields approximately 0.30 acre-feet of suspended sediment per square mile of drainage. In 1975 the Division of Water Resources, using data available in the Colorado Basin, estimated that the suspended sediment yield of the White River near Watson, Utah, is between 0.15 and 0.30 acre-feet per square mile of drainage area and recommended that a value of 0.25 acre-feet per square mile be used for the White River sediment yield until more precise sediment data on the White River became available. This value results in an annual yield of 1,600,000 tons or 1,000 acre-feet of sediment per year. The U. S. Geological Survey records show at the mouth of the White River at Ouray in 1975 a total sediment load of 1,871,509 tons (1,227 acre-feet) and for 1976 a total sediment load of 982,525 tons (644 acre-feet). The drainage area of the White River at the mouth is 5,120 square miles, while the drainage area at the proposed damsite near Watson is 4,020 square miles. Based on drainage area, the sediment load at the proposed damsite was 963 acre-feet in 1975 and 506 acre-feet in 1976 or an average of 735 acre-feet per year for the two-year period of record. - 41 -