SEDIMENT TRANSPORT AND CHANNEL CHARACTERISTICS OF A SAND-BED PORTION OF THE GREEN RIVER BELOW FLAMING GORGE DAM, UTAH, USA

The Green River is a major tributary of the Colorado River with a drainage area of 115 770 km2 in Colorado, Utah and Wyoming. The influence of Flaming Gorge Dam on sediment transport and the potential for future channel change were studied using comparative analysis of historical aerial photographs from 1952 to 1987 and geographical information systems, published sediment (1951-86) and discharge (1965-87) records, and sediment data collected during 1986-8. Since the closure of the dam in 1964, new equilibrium channel widths were apparently achieved by 1974 in the reach 161-279 km below Flaming Gorge Reservoir and by 1981 in the reach 465-509 km below the reservoir. Recent high flows have resulted in an increase in average channel width in both reaches as measured on aerial photographs taken in 1986 and 1987. Sediment data from US Geological Survey gauges on the Green River and its primary tributaries and three sites established on the Green River for this study suggest that bed material sediment transport in the Green River has now attained a quasi-equilibrium, with the river transporting just the load supplied to it. The potential for future channel changes exists, as evidenced by the response of the channel (i.e. channel widening) to the increased flows during 1983, 1984 and 1986. Future adjustments in channel characteristics should be limited to responses to changes in discharge and sediment supply and transport in the basin.