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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I 7

1993 AND 1994 FIELD STUDIES
Side channel/backwater habitats were the focus of the field study due to
their importance to both the adult and larval stages of the Colorado squawfish
and razorback sucker. Backwater morphology is partly dependent upon the
flow regime which controls the scour and fill of sediment. The high flows of
spring generally cause the backwater to become a side channel and fine
sediment that has accumulated on the bed is scoured. Some researchers
theorize that river regulation has decreased flows and caused a net filling of
these areas with sediment (Osmundson and Kaeding, 1991; Graf, 1978). The
relatively high (1993) and low (1994) peak discharges of the two years allowed
us to document the effects of flow magnitude on backwater morphology.
Methods
Three side channel/backwater sites were chosen and 25 cross-sections of
bed topography were surveyed before, during, and after the peak flows of 1993
and 1994. All cross-sections were permanently marked with rebar or metal
fence posts. Standard surveying techniques were used to measure cross-
sections in areas of shallow flow. In deeper areas such as the main channel,
cross-sections were surveyed from a boat outfitted with depth sonar (Van
Steeter and Pitlick, 1994). Characteristics of the three sites are summarized in
Table 4.