8255

• UCREFRP Catalog Number: 8255
• Author: Grams, P. E. and J. C. Schmidt.
• Title: Geomorphology of the Green River in the Eastern Uinta Mountains, Colorado and Utah.
• USFW Year: n.d.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

Grams and Schmidt

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deposition is detennined by local fan-eddy complex depositional environments, sorting is
determined by local hydraulic processes and possibly local attrition (from debris fan to
gravel bar) rather than downstream hydraulic sorting and attrition.
Like other debris-fan dominated canyons of the Colorado Plateau (Schmidt and
Rubin, 1995), fan-eddy complexes are the fundamental channel-organizing unit on the
Green River in the canyons of the eastern Uinta Mountains. More than 60 percent of all
fme-and coarse-grained alluvium is stored within these depositional units either as eddy
bars, channel-margin deposits in backwaters, .or expansion bars. This is in contrast to the
meandering reaches which store more than an order of magnitude more alluvium per km,
and have no fan-eddy complexes.
The geomorphic organization of the Green River in the eastern Uinta Mountains is
essentially similar to that of the Colorado River in Grand Canyon as described by Howard
and Dolan (1981), Schmidt and Oraf (1990), and Schmidt and Rubin (1995). In both
systems, channel geometry and gradient is correlated with the lithology exposed at river
level. Debris fan frequency is higher in the eastern Uinta Mountains; there are 3.3 fans per
km on average in the eastern Uinta Mountains but fans are never more frequent than 2.9
fans per km in Grand Canyon (Schmidt and Leschin, 1995). Nevertheless, debris fans
have a strong influence on sedimentation patterns in both systems. About 70 percent of all
.. mainstem alluvium in the study area is contained within fan-eddy complexes, either in
eddy bars, expansion bars, or channel-margin deposits in the backwater. The percentage
of fme-grained alluvium contained in eddy bars is somewhat less, and is between 34 and
63 percent in the canyon reaches. Schmidt and Rubin (1995) showed that this percent
varied between 44 and 75 percent in Grand Canyon and between 1 and 29 percent
elsewhere on the Green River.
The largest difference between eddy bars in the Green River and Grand Canyon
systems is the lack of differentiation between separation and reattachment bars in the
eastern Uinta Mountains. Th!~..may be an indication of the relative abundance of fme-