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Draft Fmal Completion Report to UDWR for Contract #93-1070, Amendment 3 5 estimated that the sediment transported into the Green River in the reach between the Yampa River confluence and the White and Duschesne Rivers was equal to the sediment exported from that reach. Sediment mass balance thus appears to be maintained for the Green River within the central Uinta Basin. Channel Change Since Flaming Gorge Dam Two studies have measured or described channel change in the Green River below Flaming Gorge Dam. Andrews (1986) studied the Green River between Flaming Gorge Dam and its confluence with the Colorado River, and Lyons and others (1992) focused on the Green River through the Uinta Basin. The following discussion highlights those results applicable to the reach that includes Ouray NWR. Andrews (1986) calculated the changes in sediment balance and discharges since closure of Flaming Gorge Dam using USGS gage records for the station near Jensen. Utah. for the period 1947 to 1981. The effective discharge, the modal value of the sediment load-duration function. was reduced 44 percent (from 580 m3fs to 325 m3fs) after closure of Flaming Gorge Dam, although no significant change in the sediment rating curve for the sand-sized fraction bad occurred. In addition. Andrews (1986) compared aerial photographs taken in 1964 and 1978 to assess changes in bankfull width at 15 cross-sections within a 97 -Ian reach that included the Ouray NWR. Andrews (1986) determined that, on average, the channel had narrowed by 13 percc;nt from 213 m to 186 m, and much of the narrowing resulted from accretion of islands to the bank (Andrews and Nelson. 1986). Andrews (1986) estimated that channel narrowing would be complete when the average channel width was 160 m, based on hydraulic geometry relations. He estimated that channel narrowing would be completed in approximately 30 years. . Lyons and others (1992) recalculated effective discharge and measured channel change in the Uinta Basin. Using more extensive photo-interpretation. and discharge and sediment records that extended to 1987, they concluded that channel narrowing had been completed by 1974, and was not as great as reported by Andrews (1986). Andrews (1986) did not include data from the large floods on the Green River between 1983 and 1986, but Lyons and others (1992) showed that these floods did increase channel width within the central Uinta Basin. While Lyons and others (1992) largely confirmed Andrew's (1986) findings, Lyons and others (1992) argued that a sediment mass balance quasi-equilibrium has already been reached in the Uinta Basin. and channel widening and channel narrowing will occur in the future as short-term adjustments to periods of high and low discharge. Although high flows such as occurred