6007

• UCREFRP Catalog Number: 6007
• Author: Carter, J. G., R. E. Valdez, R. J. Ryel and V. L. Lamarra
• Title: Fisheries Habitat Dynamics in the Upper Colorado River
• USFW Year: 1985
• USFW - Doc Type: Journal of Freshwater Ecology
• Copyright Material: YES

Backwaters

One of the more dramatic relationships seen in this analysis was
between discharge and area of backwaters (Figure 7). Two thresholds
occurred, one subtle and one more dramatic. At low flows, the surface area
of backwaters was low and represented by small discrete units formed by
shoreline depressions (Figure 3). At about 6,000 cfs, these depressions
were inundated by flow-through and many of these backwaters were lost as
others developed (Figure 5). However, when river discharge reached about
10,000 cfs, a nearly 50-fold increase in backwater area was seen. This
occurred during runoff when the river flooded adjacent low-lying depressions
1 i ke 01 d si de channel s and man-made features such as gravel pi ts.
Backwaters were less numerous at this time than during low flow, but each
individual backwater encompassed a much larger area.

The occurrence of backwaters appears to coincide with certain events in
the 1 ife history of the river fishes. Spawning for many of the riverine
species in this area occurs during the descending limb of runoff and these
large backwaters may serve as areas for resting, maturation, and spawning as
flows decreased, and backwaters become more numerous but smaller in area.
The young fish occupied these small, warm, sheltered areas to find food and
escape deep-water predators. It was a1 so noted that these large backwaters
were usually warmer than the main channel, by 1-50C. This may enable
certain species to accumulate temperature degree-days needed for
reproductive maturation.

Flooded Woodlands

The area of flooded woodlands, like that of backwaters, also increased
dramatically at about 10,000 cfs discharge (Figure 7). This habitat
consisted mostly of flooded willows and other riparian vegetation that was
surrounded by water when the river exceeded its common-flow banks. This
habitat appears to be important to small fish as feeding areas and as
shelter from the main channel turbulence during runoff.

Embayments and Concavities

The areas of embayments and concavities (Fi gure 7) did not bear a
predictable relationship to discharge. These small habitats depend on
shore1 ine depressions which apparently occur randomly and at all el evations
within the floodplain. Embayments usually occur more frequently in sandy
areas where shi fting of the substrate is more common than in rocky areas
such as the study area (Valdez and Wick 1981). Larval fish surveys in
Colorado during 1979-1981 indicated that shorel ine embayments and
concavities are an important habitat feature to larval Colorado squawfish
(Haynes et a1. 1984).

Rapids, Runs and Riffles

The occurrence and areas of rapids and runs (Fi gure 8) seemed to follow
a similar pattern. However, rapids occurred only above 10,000 cfs, when the
ri ver turbu1 ence was severe, enough to create these areas. The area of
riffles (Figure 8) occurred in inverse relationship to those of rapids and
runs. Runs and riffles appear to be important habitats for suckers and dace
as feeding areas and perhaps as spawning areas (Valdez et al. 1982).
However, few fish were found in rapids.

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