7920

• UCREFRP Catalog Number: 7920
• Author: Van Steeter, M. M., J. Pitlick and B. Cress.
• Title: Aerial Photograph/GIS Analysis and Field Studies of the Grand Valley and Ruby-Horsethief Canyon of the Colorado River.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

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Table 4. Summary of Backwater Field Site Characteristics

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location
(river mile)

Dso
(mm)

number of
cross-sections

characteristics at different flows
low med high

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Site 1 (162.5)

50

6

5 B B W SC

Site 2 (159.9)

48

10

B W SC SC

Site 3 (1755)

55

8

B W B W SC

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SB: stranded body of water
BW: backwater
sC: side channel

Results

The 1993 flows caused scour oEO-25m of fine sediments from the

mouth of the backwater sites, but few changes occurred at the upstream ends
where the substrate is primarily gravel. Fine sediments were deposited along
the banks at most cross-sections, and vegetation was generally abraded but not
uprooted. Scour at the mouth of these backwaters is important for
maintaining fish access at low flows. It appears that the high flows of 1993
were important for scouring backwater mouths, but one year of high flow does
not appear to be enough to greatly change the morphology of the upstream
end or to uproot existing vegetation.
The flows of 1994 were low and only small amounts of scour and
deposition were observed. There was 0-1.7m of deposition of fine sediment at
the mouths of these backwaters, but other changes were minor. These trends,
are most evident at site 3 (Fig. 11). Site 2 showed fewer changes because it is a
side channel even at moderate flows and substantial amounts of fine

sediment do not accumulate (Fig. 10). Site 1 shows minimal changes at its
mouth because of dense root mats of grasses which stabilize sediment (Fig. 9).