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

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time. There was little change in average bed elevation in the downstream pan of the study reach (Fig. 20). Adjustments

of the topography of the upstream compound bar caused by the 1994 flood resulted in a slight decrease in the average

elevation of the entire bed. Elsewhere, average bed elevations after the 1994 flood were more similar to those that had

existed prior to passage of the 1993 flood (Fig. 20).

Geomorphic Characteristics and Changes in the
lO-km Study Reach

Fourteen sites in the lO-km study reach were consistently occupied by bank-attached compound bars or point

bars during the study period (Appendix D). In addition to these spatially stable bars, there were many transitory mid-

channel bars. The channel deposits were associated with 10 bank-attached compound bars, most with some stabilizing

vegetation. 3 point bars, and a deposit upstream from a flood return channel that was active only during high flows (Fig.

12). The low flow morphology of these deposits varied greatly from year to year, but the location of these deposits

changed little during this study. Mayers (1995, pers. comm.) states that location of these deposits has changed little

since 1966.

In 1992, during summer low flow, the channel in the lO-km reach had many bank-attached and mid-channel

bars. These conditions were similar to the conditions in the 1.5-km reach. In July 1992, there were 9 mid-channel bars,

and 4 bank-attached bars dissected by one or more chute channels (Appendix D). The channel form was complex and

had many flow-dissecting features. The September 1992 videos were made during a period of lower discharge than the

other video flights (Table 4). The September videos show that the lateral extent of bars visible in the July 1992 videos

(46 m3fs) appeared to have increased, but there was no change in their location. This indicates that visible changes in

morphology were probably an artifact of the lower discharge at the time of the September 1992 Reclamation overflight

After the 1993 spring flood, the number of mid-channel bars and deposits dissected by chute channels at low

flow was reduced from 14 to 3; 2 of these were associated with dissected bank-attached bars. This, and maps of the

reach (Appendix D), demonstrate the simplification of channel morphology from its more complex condition prior to the

1993 flood. Mid-channel deposits were removed and bank-attached compound bars or point bars were consolidated into

single bank-attached units such as occurred within the 1.5-km study reach (Appendix D).

The winter low flows of 1993-1994 increased the number of mid-channel bars to 18 by April 1994. Deposits

were emergent at55.5 m3fs in 8 mid-channel locations whereas no deposits were emergent at 51 m3fs in September