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

Main Channel Cross Sections
Cross sections of the main channel were surveyed every 5 miles, extending from RM 185
downstream to RM 130 (Fig. 1). Survey measurements in the 15-mile reach indicate relatively
minor changes at cross sections RM 185 and RM 175 in 1995, but what appear to be much more
significant changes at RM 180 (Fig. 10). We are not certain, however, that the changes at RM 180
are 'real' because during the 1995 survey we were unable to find either one of the cross section
endpoints, and thus it was not possible to re-locate the section line exactly (at least one, if not both,
of the endpoints for all other sections were located, and thus these surveys are accurate within the
limits of the techniques). In any case, the most recent surveys of RM 185 and RM 175 indicate
localized scour and fill of up to 0.5 m in the channel (Fig. 10), but little change overall.
Measurements of cross sections in the 18-mile reach indicate similar trends: localized scour
and fill, but little change in morphology overall (Fig. 11). Several meters of the right bank were
eroded at RM 170, and about 0.5 m of sediment was eroded off the top of the bar at RM 155.
Otherwise, the changes observed at cross sections in this reach were minor.
Cross sections in Horsethief Canyon likewise exhibited localized scour and fill of up to 2 m
in the main channel, but generally much smaller changes (Fig. 12). No appreciable changes in
channel morphology occurred in this reach, largely because the river is more constrained here by
bedrock. The remaining two cross sections, RM 135 in Ruby Canyon and RM 130 in the alluvial
reach upstream of the Westwater boat launch, exhibited contrasting responses (Fig. 13). The cross
section at RM 135 showed no discernible change, whereas the cross section at RM 130 showed the
most significant change of any that we measured More than 30 m of the left bank was eroded at
RM 130, taking out the original left endpoint of the section (the right endpoint was located and the
section line re-established on the basis of ground photographs). The changes at RM 130 appear to
be the direct result of channel instability in the area a few hundred meters upstream. This area is
characterized by a number of channels and bars that continue shifting location. It also includes a
site where spawning activity has been suspected in the past (D. Osmundson, pers. comm.), and
thus it may be important to continue monitoring channel change in this area.
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