8115

• UCREFRP Catalog Number: 8115
• Author: Pitlick, J., M. V. Steeter and M. Franseen.
• Title: Effects of Recent High Flows on Selected Reaches of the Upper Colorado River.
• USFW Year: 1996.
• USFW - Doc Type: Boulder, CO.
• Copyright Material: NO

In order to understand how the river responds to seasonal variations in discharge and
sediment load, we have established a number of study sites in the reaches described above. Three
of our study sites are backwaters' formed where flow splits around a bar or island into aside
channel. Compared to the main channel, backwaters are characterized by lower flow velocities,
lower depths and higher water temperatures, and thus, they are considered to be important habitat
for the endangered fishes (Stanford, 1994). The backwater study sites consist of a series of
surveyed cross sections running from the upstream entrance of the side channel to the downstream
exit where the flow rejoins or backs up from the main channel. These cross sections are arrayed
such that we can observe whether there is scour or fill at the entrance and exit, which are the two
key points governing fish access and the flow of water and sediment through the side channel.
These sites have been surveyed repeatedly over the past 3 years.
To place these site-specific observations into a somewhat broader context we separately
measured a series of main channel cross sections, proceeding at 1-mile intervals from Palisade to
the Westwater boat launch, river miles (RM) 185 to 128. Cross sections in the 15- and 18-mile
reaches (RM 185 to RM 153) were surveyed in 1993; cross sections in the Ruby and Horsethief
Canyon reaches (RM 152 to RM 128) were surveyed in 1994. Results of this and related work are
described in two previous reports (Van Steeter and Pitlick, 1994; Van Steeter et al., 1995).
The present report updates this work using data obtained in late summer of 1995 following
a period of high snowmelt runoff. Above-average precipitation and cool weather in the spring of
1995 increased snowpacks in the upper Colorado River basin dramatically- up to 300% of normal
in some areas- and the ensuing runoff was characterized by relatively high flows of long duration.
At the request of the U.S. Fish and Wildlife Service (USFWS) and the Bureau of Reclamation
(USBR), we re-surveyed some of our field sites to assess the geomorphic effects of these high
flows. Cross sections at the 3 backwater study sites were surveyed in their entirety. In addition,
we re-surveyed 12 main channel cross sections. The following discussion provides further details
of the 1995 hydrograph and a summary of our observations of channel changes at selected sites.
Additional cross section data not discussed below are presented in an appendix.
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