7820

• UCREFRP Catalog Number: 7820
• Author: Rakowski, C. L., J. C. Schmidt and T. A. Crowl.
• Title: Geomorphic Response of a Sand-Bed River to High Discharge; Effects on Colorado Squawfish Nursery Habitat Availability, ‎(poster presented at 1993 Fall Meeting of American Geophysical Union)‎.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

INTRODUCTION

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The study site is located on the Green River, within the Ouray National Wildlife Refuge.
About 50 percent of river flow at the study site is controlled by water releases from Flaming Gorge
Dam; the remainder of the streamflow originates from the unregulated Yampa River.
Colorado squawfish (Ptychocheilus lucius) are endemic to the Colorado River basin and were
once abundant. The fish was included in the original list of endangered species by the US Fish and
Wildlife Service in 1967. Squawfish spawn on cobble and gravel substrate on the lower Yampa
River on the descending limb of the spring snowmelt hydrograph. Larval fish emerge after an
incubation time of about I week and are transported or move downstream. Larval fish occupy
stagnant flow habitats associated with emergent sand bars in the Ouray reach (Fig. 1) (Tyus, 1990).
These fish remain in these sites throughout the summer and fall. One objective of water release
management of Flaming Gorge Dam is to maximize the available areas of stagnant water and eddies
(backwaters) to maximize and maintain nursery habitat availability.

Research Objectives

. Characterize the geomorphology of Colorado squawfish nursery habitat
. Determine if different geomorphic settings give rise to nursery habitats of different
qualities
. Develop flow recommendations for formation and maintenance of high quality nursery
habitat.

1993 Field Season Objectives

1 Characterize the geomorphology of the reach.
2 Quantify the extent and magnitude of bed response to the passage of a "normal" flood,
occurring after a seven-year drought period.
3 Measure changes in channel cross sections on the descending limb and during low flow
regimes. Establish a data set to further calibrate the bed behavior model of Andrews and
Nelson (1989).
4 Relate bar changes to changes in available Colorado Squawfish nursery habitat.

STUDY SITE

The Green River near Ouray is characterized by alternate and mid-channel bars that have
largely remained fixed during the past 30 years. Reduced flood peaks have caused channel
simplification (e.g. filling of some secondary channels), although there have also been many areas
of bank erosion.
The study reach was established by Andrews and Nelson (1989), who applied a numerical
flow and bed behavior model to this reach. Their cross-sections were replicated by the U.S. Fish and
Wildlife Service and Bureau of Reclamation (1. Lyons, G. Smith, written comm.) in 1987 and 1990.
We reoccupied this site in fall 1992.

The intensive study site is 1.3 km in length (Fig. 2), and is located within a 16-km reach