8157

• UCREFRP Catalog Number: 8157
• Author: Pitlick, J., M. V. Steeter, B. Barkett, R. Cress and M. Franseen.
• Title: Geomorphology and Hydrology of the Colorado and Gunnison Rivers and Implications for Habitats Used by Endangered Fishes.
• USFW Year: 1999.
• USFW - Doc Type: \
• Copyright Material: NO

develop physically based models for discharges that will improve existing fish habitats. The
specific objectives of this study were as follows:
1) Determine how reservoir operations have changed the annual flow hydrograph and
sediment-transport capacity of the upper Colorado River;
2) Quantify the effect of these historical changes on channel morphology;.
3) Measure existing channel characteristics and responses to snowmelt runoff events; and
4) Provide recommendations for flows that will maintain or improve existing habitats.
The present study focuses on a 90-km segment of the upper Colorado River from Palisade, CO to
Westwater, UT. This segment provides important habitat for Colorado squawfish and razorback
sucker and marks the upper limit of their range on the main-stem Colorado River. We also include
analyses of a 85-km reach of the lower Gunnison River between Delta and Grand Junction, CO.
In conducting this work we were fortunate to have abundant flow and sediment load data, high
quality aerial photographs, and several years of above-average runoff in which we could observe
the effects of high flows on the river. Our results not only provide key information for fisheries
biologists and water resource engineers, they also give added insight into questions about rates of
channel change, mechanisms of cross section and profile adjustment, and processes of sediment
transport in gravel-bed rivers.
RELATION BETWEEN FISH HABITATS AND GEOMORPHOLOGY
The present study focuses on habitats used primarily by Colorado squawfish. Of the four
endangered species, Colorado squawfish are perhaps the most studied, and they are certainly the
most abundant of the endangered species in the study area (Stanford and Ward, 1986). The
population of razorback sucker in the upper Colorado River is very small, and possibly no longer
self-sustaining (Osmundson and Kaeding, 1991). Some of the information in this report is
applicable to razorback sucker, but this species is considerably different from Colorado squawfish,
thus we restrict most of our analysis to processes and conditions that affect the latter species.
Ecology and Habitat Use
The ecology and habitat needs of Colorado squawfish have been described in detail in a number of
studies (reviewed by Tyus, 1991 and Stanford, 1994). It is important to note here that much of the
present understanding of Colorado squawfish ecology is based on studies of a relatively large
population in the Green-Yampa River system. Early studies of this population showed that
individual squawfish made long (> 100 km) seasonal migrations to spawn in specific reaches of
the Green and Yampa Rivers (Tyus and Karp, 1989; Tyus, 1991). Similar studies of the
Colorado-Gunnison River subpopulation of squawfish suggest that, while there is a tendency for
adults to congregate near Grand Junction during the spawning season, they migrate relatively short
distances (23 km, on average), and they spawn in widely separated reaches (McAda and Kaeding,
1991). For whatever reason, squawfish in the upper Colorado River are not as specific in their
selection of spawning sites as their Green-Yampa counterparts are. It does appear, however, that
the basic requirements for spawning are similar. Spawning occurs several weeks after the peak in
the snowmelt hydrograph between late June and early August when water temperatures reach 18-
22°C (McAda and Kaeding, 1991). In the few instances where spawning has been observed in the
upper Colorado River, the fish were seen congregating near dissected gravel bars formed by loose,
open-framework particles (D. Osmundson, personal communication), similar to what has been
observed on the Yampa River (Lamarra et al., 1985; Harvey et al., 1993).
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