The Green River is one of the principal tributaries in the Colorado River basin and drains 44,700 m2 in Wyoming, Colorado, and Utah. Since October 1962, flows of the Green River have been regulated by Flaming Gorge Reservoir, which is located 412 river miles upstream from its confluence with the Colorado River. Mean annual runoff has not been affected by the reservoir. The duration of the relatively large discharges that transport most of the annual sediment load, however, has decreased significantly. As a result, the mean annual sediment discharge has decreased by 54% to 3.21 × 106 tons from 6.92 × 106 tons at the Jensen gage located 105 river miles downstream from the reservoir and by 48% to 8.83 × 106 tons from 17.0 × 106 tons at the Green River, Utah, gage located 290 river miles downstream from the reservoir. Sediment supply to I he channel equals the annual transport within a relatively short distance, 68 river miles, downstream from the reservoir. Downstream from river mile 166, the supply of sediment from upstream plus tributary inflow exceeds the transport of sediment by ∼5.4 × 106 tons per year on an average. The quasi-equilibrium that appears to have existed prior to the reservoir no longer occurs along a majority of the Green River.
In response to the reduced peak discharges, the bankfull channel width of the Green River has decreased by ∼10%. Adjustment of the channel to decreased peak flows and altered sediment loads is nowhere complete. At present, it appears that a century or more will be required for the Green River to adjust to the effects of Flaming Gorge Reservoir.