WSP01392

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 6/1/2000
• Author: CDOW
• Title: Riverine Fish Flow Investigations 2000
• Water Supply Pro - Doc Type: Publication

of blue head sucker in this reach, but correlations between habitat and fish are not available.

Bluehead sucker composition below the study site was 15% and 25% above the study site and

it was also a casual observation that there was less deep riffle habitat in those reaches.

Even though flows that have been modeled so far are not considered low or

problematic flows, the habitat composition presented in the results can be used to indicate the

general nature of these sites. This is because habitat composition is primarily a function of

channel morphology and gradient. Rimes are areas of higher gradient, so as flow drops,

depths, velocity and wetted area of the riffle habitat decrease. At the flow of2,000 cfs on the

IS-mile reach and 600 cfs for Duffy, the channel perimeter is nearly wetted so habitat at these

flows should be near maximum diversity. As flow drops, the rime habitats decrease at the

highest rate and the area and percent of rime both decline. At reduced flow, surface area of

pools decrease at a lower rate so the area of pools will decrease but the percentage of pools

will increase. It is expected that habitat diversity will simplify as flows drop.

The two study sites have opposing extremes in terms of habitat composition. The 15-

Mile reach is primarily high-gradient deep habitats and the Duffy is primarily low-gradient

shallow habitats. In order to make better comparisons between fish and habitat the plan in

2000 is to map habitat and sample fish in the Lily Park area of the Yampa and also above the

study site on the IS-Mile reach. Lily Park area has been shown to have a high composition of

native fish (Anderson 1999) and also has a long stretch of high gradient habitat and this

allows the opportunity to determine if similar habitats produce similar fish between the two

rIvers. Also the Lily Park section has a low gradient area near the mouth of the Little Snake

River. The new site in the IS-mile reach will probably be in an area with a lower

composition of riffle habitats. Both the above and below sections sampled for fish in the 15-

Mile reach had a lower percent of blue head sucker in the sample. These additional sites

should fill the gaps and improve relating the fishery to habitat features.
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