9455

• UCREFRP Catalog Number: 9455
• Author: Lyons, J. K., M. J. Pucherelli and R. C. Clark.
• Title: Sediment Transport and Channel Characteristics of a Sand-Bed portion of the Green River Below Flaming Gorge Dam, Utah, U.S.A.
• USFW Year: 1992.
• USFW - Doc Type: R-92-08,
• Copyright Material: NO

INTRODUCTION
The Green River, a major tributary of the Colorado River originating in southwestern
Wyoming, has a drainage area of 115 770 square kilometers in Colorado, Utah and Wyoming
(fig. 1). Iorns et al. (1965) described the surface water and sediment yield data for the Green
River Basin. The headwater areas in the northern and eastern edges of the Green River Basin
serve as the principal areas of water source. Semiarid portions of the basin at lower elevations
contribute the majority of sediment. The Green River is controlled by two reservoirs, Fontenelle
and Flaming Gorge. Flaming Gorge Dam, downstream from Fontenelle and completed in 1962,
has an active capacity of 4.3 million cubic dekameters. The average annual inflow to Flaming
Gorge Reservoir is about 1.5 million cubic dekameters. The dam is located 660 kilometers
upstream from the confluence of the Green and Colorado Rivers.
Green River Studies Performed by Others
The study reported herein continues the work reported by Andrews (1986), who studied the
impact of Flaming Gorge Dam upon channel morphology and suspended sediment transport of
the Green River. Andrews described post-reservoir flow pattern changes and suspended
sediment transport measured at stream-gauging stations, and reported channel width trends
for short reaches of the river following dam closure in 1963. Andrews concluded that a condition
of quasi-equilibrium indicated by the absence of net aggradation or degradation existed on the
Green River before 1962. Construction of the dam caused changes in channel width and flow
and sediment patterns.
Andrews reported channel degradation for the Green River upstream from the Yampa River,
where sediment-free releases from Flaming Gorge occur and the majority of sediment load is
obtained from the bed. Downstream from the Yampa River to the Duchesne River, Andrews
noted a new quasi-equilibrium. Below the Duchesne River, he described aggrading river
conditions. Andrews concluded that the quasi-equilibrium in existence prior to reservoir
completion no longer exists along the majority of the Green River. He also stated that the
potential for future significant channel narrowing exists for the Green River. Using a constant
rate of channel narrowing calculated by comparing historical aerial photography, he estimated
that this narrowing may not be complete for about 30 years in a study area located about 170
kilometers below Flaming Gorge Dam.
Andrews and Nelson (1989) studied the effects of discharge variations on a mid-channel bar
located about 250 kilometers below Flaming Gorge Dam in the Green River. Their comparison
of historical aerial photographs taken about the time of construction of Flaming Gorge (1964) to
those taken in 1986 demonstrated the long-term stability of this bar. They reported results of a
numerical model study that described evolution of bar topography over a nearly 10-fold range in
discharge. Their calculated rates of bar evolution indicate a rapid adjustment in bar topography
in response to changes in discharge.
These topographic changes, estimated to occur within several days to a few weeks following a
change in discharge, were observed for discharges of 475 cubic meters per second