8214

• UCREFRP Catalog Number: 8214
• Author: Modde, T., D. Irving and R. Anderson.
• Title: Habitat Availability and Habitat Use of Endangered Fishes in the Yampa River during Baseflow Periods.
• USFW Year: 1997.
• USFW - Doc Type: Vernal, Utah and Grand Junction, Colorado.
• Copyright Material: NO

or Class II pools. The primary habitat available to Colorado squawfish at all simulated flows (1-500
cfs) were shallow run habitats.

Combined clusters in Strata 2,3, and 4

Figure 10 and Appendix 2, Tables 1-5 show habitat composition when all 28 cross sections in
strata 2, 3 and 4 are combined. Total river reach represented by the 28 cross sections (5,805 ft) is
3.1 % of Strata 2,3 and 4 (35.6 miles). Shallow runs (unusable habitat) are the most common
habitats available at flows between one and 500 cfs.

Figure 11, gross habitat versus flow, shows a rapid increase in wetted surface area between one
and 100 cfs, but between 100 and 500 cfs surface area increases linearly. Usable surface area
increases in a fairly linear relationship with flow between 1 and 250 cfs. The amount of usable area
at 200 cfs is only double that of what is projected at 1 cfs.

With only one cfs of flow, the wetted surface area of the river models to be 9,627 ft.2/1 00 ft. in
strata 2 (rm 20.0-45.5), 17,414 ft. 2/1 00 ft. in strata 3 (rm 45.5-51.0), and 42,787 ft. 2/1 00 ft. in strata
4 (rm 51.0-54.0) (Appendix 2, Tables 1-5).

The mean stream width were 10.1 ft. in strata 2 (rm 20-45.5),15.5 ft. in strata 3 (rm 45.5-51.0),
and 40.0 ft. in strata 4 (rm 51.0-54.0) at one cfs. The river maintains width at very low flows in
clusters 3 and 4 because of its flat gradient and the low width/depth ratio.

A width/discharge relationship was determined by averaging the widths of each cross section in
a sequence for each of the simulated flows. (Mean cross-sectional width is different from the mean
stream width as determined by Appendix 2, Tables 1-5). The width/discharge relationship was
highly variable for cross sections within a cluster and between clusters. High gradient habitats
(riffles) had narrower widths at low flows than low gradient habitats with low width/depth ratios.
Cluster 2 (rm 20.0-45.5) had the lowest average cross sectional width at 1 cfs (10.1 ft.) and Cluster
3 (I'm 45.5-51.0) had the widest average cross section width at 500 cfs at 290 ft. (Figure 12).
Between one and 100 cfs, stream width increases rapidly with flow, but at flows between 150 and
500 c[<; the relationship is fairly linear. Mean channel width, grass line to grass line, were found to
average about 229 ft. for cluster 2 (rm 20-45.5), 458 ft. For cluster 3 (rm 45.5-51.0), and 306 ft. for
cluster 4 (rm 51.0-54.0). The mean cross section width of strata 2 at 500 cfs was 139 ft. or about
6] % of the bankfull width, 298 ft. For cluster 3 or about 65% of the bankfull width, and 227 ft. For
cluster 4 or about 74% of bankfull width.

Coefficients of variation for width were highest at the lowest flow (1 cfs) and decreased with
increased flow (Figure 13). This is expected since riffle and run widths become more uniform as
flow increases. The relationship between width C.V. and flow was curvilinear at between one and
100 cfs with an inflection point at 40 cfs for cluster 2 (rm 20-45.5),50 cfs for cluster 3 (rm 45.5-
51.0), and 60 cfs for cluster 4 (rm 51.0-54.0).

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