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

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

41

1993. There was an apparent overall decrease in the lateral extent of the bars, and this lateral erosion was confirmed by

cross section surveys in the 1.5-lan reach. Figure 21 illustrates this style of lateral bar erosion.

The gross planform of the channel changed little as a result of the passage of the low flood peak in 1994. The

total number of mid-channel bars decreased slightly (from 15 to 13). but comparison of the April 1994 and July 1994

videos showed that few of these bars were in locations where mid-channel bars had existed prior to the flood. The

bank-attached compound bars changed little in location or in stream-wise extent, but their shorelines became more

complex upon emergence at low flow (Appendix D).

Flow and Sediment Transport Model
The model used by Andrews and Nelson (1989) was modified as described in the Methods section. and run for
three flood scenarios. For model stability during longer simulations, it was necessary to include the additional upstream
cross sections. The earliest date for which cross-section data that included the additional upstream cross sections and
had a discharge above base flow was May 14, 1994. These survey data, measured at a discharge of256 m3fs, were used
for all flow simulations.

Simulated Topography and Sediment Transport

Comparisons of ~odel-generated topography and mapped field data were made to evaluate model resolution of

real channel features. Figure 22 compares a contour map of splined topography generated from the cross sections to the

pseudo-elevations generated from the video prints and the detailed topography of the bank-attached bar. Channel

topography generated by splining the cross-section data described the large-scale topographic features of the 1.5-lan

study reach (for example, the location of the bank-attached and point bars and the thalweg). Comparison of the bank-

attached bar's 1994 detailed topography and the July 1994 model topography (Fig. 22) demonstrated that the spacing of

the cross sections of this study was not sufficiently close to resolve the finer details and complexity of topographic

features, including those that, in some years, form nursery habitat.

Average bed elevation from the model generated topography and from the cross section surveys are compared

in Figure 23. The average bed elevation was calculated for the surveyed cross sections using data for the portion of the

channel delineated as detailed in Appendix C. These calculations do not include elevation data points above 94.0 m

found near thecbannel margin. The model topography is for the whole channel, and includes points up to 95.4 In.