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ANl{JAL SUSPENIED-SEDlMENI' LOADS IN WE e GREEN RIVER AT GREEN RIVER, tJI'AH. 193 0-82 By Kendall R. '1h~on ABSTRAC1' '!he Green River above the gaging station (05815000) at Green River, Utah, drains about 44,850 square miles in Utah, Coloraoo, and wyoming. The average annual precipitation near the station was 6.11 inches. During 1930-82, the U.S. Geological Survey collected records of fluvial sediment at station 09315000. Based on these records the mean annual suspended-sediment load was about 15,630,000 tons, ranging from 1,780,000 tons during 1934 to 43,400,000 tons during 1937. '!he minimum daily load of 54 tons was on September 27, 1956, and the maximum daily load of 2,230,000 tons was on July 11, 1936. e Analysis of the suspended-sediment records collected from 1930-82 at station 09315000 indicated that the accuracy of the records is fair prior to 1945 and good for the remaining period of record. The records after 1945 reflect the use of improved sampling equipment. A double-mass curve showed changes in relationship between annual suspended-sediment load and annual stream discharge. The first change occurred approximately between water years 1944-46 and coincides with a change in sampling equipment. The U.S. 0-43 suspended-sediment sampler was first used at station 09315000 during October 1945 Cl946 water year). The second change, which occw:red approximately between water years 1963-65, coincides with the completion of Flaming Gorge Dam during November 1962 (1963 water year) upstream from the station. The mean annual suspended-sediment loads were reduced ~ about 35 percent at station 09315000 after the completion of the dam. Other factors may have been involved or responsible for these changes, but their identification is beyond the scope of this relX)rt. The data collected after 1965 provided a basis for a predictive model. If, for example, an annual stream discharge of 4,000,000 acre-feet were used, the annual suslXIDded-sediment discharge is Iredicted to be 7,860.000 tons; and it could range from 3,400,000 to 12,100,000 tons at a 9Q-percent confidence level. It is possible, therefore, that any estimate using this model could have about a 50-percent error at a 9Q-percent conf idence level. The variability of the annual suspended-sediment loads at station 09315000 is otNious. ' The localized nature of precipitation in the basin and the variation in geology upstream from the gaging station oontribute to this variability. ~ e 1