7208

• UCREFRP Catalog Number: 7208
• Author: Lyons, J.
• Title: Green River Channel Characteristics Below Flaming Gorge.
• USFW Year: 1989.
• USFW - Doc Type: Denver, Co.
• Copyright Material: NO

INTRODUCTION
The Green River is a major tributary of the Colorado River with a drainage
area of 44,700 square miles in Colorado, Utah, and Wyoming, see figure 1.
The surface water and sediment transport characteristics of the Green River
Basin were described by Iorns et al. [1]. 1/ Originating in Southwestern
Wyoming, the Green is controlled by two reservoirs, Fontenelle and Flaming
Gorge. Flaming Gorge Dam, downstream of Fontenelle, was completed in 1962 and
is located 410 river miles upstream of the confluence of the Green and
Colorado.
The impact of Flaming Gorge upon channel morpholo and ediment ?transaorc, of
t he Green is the focus of this report. a stabili of t e present-dy an-
el orm is also of interest as continuing c annel changes may adversely
impact the habitat conditions required by endangered fishes endemic to the
Green. Aerial photography interpretation, analysis of gauge cross section
data, and collection of suspended sediment and bed-material data were done for
this study. The portion of the Green studied for this report extends from
river mile 94 near Green River, Utah, to river mile 310 near Jensen, Utah.
Williams and Wolman [2] summarized the observed changes in alluvial rivers
downstream of reservoirs. The majority of these studies were for rivers in
the semiarid Western United States. Flood peaks were generally reduced
following reservoir completion but n es 'n other water discharge charac-
teristics were variable. Suspended sediment `load were decreased for long,
reaches below the reservoirs studied. Channel degradation, the lowering of
the bed of the river, was frequently reported following the closure of the
dams. The majority of observed channel degradation occurred during the first
decade or two after dam closure.
The impact of Flaming Gorge upon channel morphology and suspended sediment
transport of the Green has been previously studied by Andrews [3]. He
described changes in flow pattern and suspended sediment transport as measured
at stream-gauging stations along the Green as well as data on channel dth
reduction of the Green following closure of Flaming Gorge in 1963. A(Vper-
cent reduction in mean annual suspended sediment load was noted by Andrews for
the Geological Survey gauge near Jensen, Utah, (see figure 1) following 1963 and
measurements of an for a short reach of the Green in the vicinity
of Jensen showed a 13 percent reduction from 1964 to 1978. Andrews concluded
that prior to 1962, a condition of quasi-equilibrium existed in the Green
channel. That is, ver a period of?eam the transport of sediment out'df a
given river reach equaled the supply of sediment into the reach. Regulation
of the river by Flaming Gorge di4j.upted this condition; ktd ng the ri ver to
adjust to different flow andsediment patter s.
Andrews reported channel degradation for the upstream reach from the dam to
the Yampa River confluence where sediment transport out of the reach exceeded
that contributed by the tributaries. Since releases from Flaming Gorge are
1/Numbers in brackets refer to entries in the biblography.