8251

• UCREFRP Catalog Number: 8251
• Author: Rakowski, C. L. and J. C. Schmidt.
• Title: The Geomorphic Basis of Colorado Squawfish Nursery Habitat in the Green River Near Ouray, Utah.
• USFW Year: 1996.
• USFW - Doc Type: #93-1070,
• Copyright Material: NO

1 I

Draft Final Completion Report [0 UDWR for Contract #93-1070, Amendment 3

32

model used by Nelson and Smith (I 989b) for the bed evolution model was designed for channel reaches where the most

upstream and downstream cross-section towgraphies were identical, and the downstream cross-section's flow

distribution was used as input at the top of the reach. The 1.5-km study reach at Ouray NWR did not satisfy this
condition. Additional code changes were made to allow the discharge to vary. In this approach. initial topography with
a discharge that over topped the bars was used. Unsteady flow conditions were simulated by using the field-measured
stage-discharge relationship from the Ouray site to determine the stage change necessary for each simulated discharge
change. In addition, m~cations were made to allow the overall channel roughness to vary with discharge, such that
the roughness was adjusted sufficiently to maintain a nearly constant water surface slope through the reach. Measured
slope through the 15-km reach was approximately 0.0002 m/m at all discharges; the flow model maintained this slope
within a 2-cm tolerance such that the average slope was between 0.000191 to 0.000213 during all model runs.
There were some limitatio~ to this approach. By using the initial lower flow topography, vertical banks were
assumed for the channel at higher discharges. This was an appropriate assumption for the channel topography
measured in the study reach. The radius of curvature for each cross section was not recalculated for each change in
discharge. While the radius of curvature does change with changes in discharge, the greatest changes occur for lower
discharges that expose mid-channel and bank-attached bar deposits. These lower discharge conditions were prohibited
in this model formulation. This approach also assumed that the water surface slope is relatively constant for a range of
discharges. While this assumption would not be appropriate for shorter or higher gradient reaches, it was a reasonable
assumption for the 1.5 km study reach.

Linkages Between Scales

Validation of Video Work

From the digitized video prints, it was possible to observe the overall channel behavior of the 10-km reach

such as the existence and persistence of bars and other features. From the interpreted UDWR data and Reclamation

video prints, changes in the location. geomorphic setting and relative quality of available habitat were discerned. Using

the GIS maps of bar topography, the area of habitat digitized from the videos for this reach were validated