9520

• UCREFRP Catalog Number: 9520
• Author: Haines, G. B., D. Irving and T. Modde.
• Title: White River Base Flow Study for Endangered Fishes, Colorado and Utah, 1995-1996.
• USFW Year: 2004.
• USFW - Doc Type: 5D,
• Copyright Material: NO

for all White River flows. This was because Yampa River fish used depths> 1.2 m and these were

relatively rare in the White River. And finally, a fourth curve was the maximum WUA score

possible, i.e., the total surface area available. It showed that suitable habitat for Colorado

pikeminnow was less than half the total surface area available.

Fish Passage
Table 6 summarizes the thalweg (i.e.,maximum) depth at each riffle cross section at flows

between 100 and 300 cfs. A discharge of300 cfs produced thalweg depths >30 cm for 47 of 49

riffle cross sections, and the two that did not had a depth of 27 cm. At 250 cfs, 46 thalweg depths

were >30 cm; at 200 cfs, 45; at 150 cfs, 45; and at 100 cfs, 45 had depths> 30 cm. One of the

shallowest riffles was located just below Taylor Draw Dam at RM 104.4, the other shallow riffles

were all between RM 20 and 48.

Frequency of Low Flows

The historic hydrograph (1979-1996) showed that mean base flow (August through

October) discharge ranged from 272 to 939 cfs. The 500,10 exceedance discharge for August

through October was 399 cfs. A discharge of 150 cfs during the same period had an exceedance

value of about 95% (Figure 11). White River discharge during the base flow period 1923 to 1997

had dropped below 200 cfs less than 5% of the time and below 150 cfs less than 1 % of the time.

DISCUSSION
This study took two approaches for identifYing a base flow that would protect the needs

of adult Colorado pikeminnow in the White River, protection of resting and foraging habitats and

protection of riffle habitat to maintain biological productivity that supports the Colorado

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