8252

• UCREFRP Catalog Number: 8252
• Author: Allred, T. M. and J. C. Schmidt.
• Title: Channel Narrowing of the Green River Near Green River, Utah
• USFW Year: 1999.
• USFW - Doc Type: History, Rates, and Processes of Narrowing.
• Copyright Material: NO

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EXECUTIVE SUMMARY.
The Green River is the longest tributary of the Colorado River. Near the
town of Green R{ver, Utah, the Green River narrowed in 2 discrete phases
during the twentieth century. The first phase of narrowing decreased average
width by about 5% and occurred between about 1930 and 1940 when the
nagnitude of the 2-yr flood, mean annual discharge, and effective discharge
decreased by about 30%,28% and 37%, respectively. During this first phase of
narrowing, saltcedar (Tamarix spp,), an invading non-native tree, began to
establish itself in the study area, but botanists of that time did not describe the
tree as "abundant." Channel width was stable in the 1940's and 1950's even
though saltcedar were becoming abundant on the river's banks. Further
. narrowing, of an additional 14%, occurred after 1959. This latest period of
narrowing began following 3 successive years when the magnitude of floods
was less than the present 1.5-yr recurrence flood and when saltcedar was
abundant along the river. The deposits that comprise the banks of the
narrowing Green River are composed of the suspended load of the river, and
these alluvial deposits are characterized by horizontal layers which indicate that
they formed by vertical accretion. We propose a mechanism to explain the
coarsening upward sequence of beds found in these vertically-accreted
deposits.
These changes in the channel of the Green River are based on analysis
of more than 2600 discharge measurements made by the U.S. Geological