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

have similar curve break values as wetted perimeter is not surprising because they are governed

by similar hydraulic dynamics.

The Instream Flow Council (2002) concluded that wetted perimeter should be considered

only one component of a recommendation that uses additional analyses, and that it does not

provide the necessary regime of flows that is critical to riverine ecology. They recommended "

. . that the flow prescribed be that discharge that covers at least 50% of the wetted perimeter in

streams that are less than 50 feet wide (and between 60 and 70% in larger streams. . .) or the

breakpoint on the wetted perimeter discharge relation, which ever is higher." In this study, that
flow was 161 cfs.

Fish Passage

Flows >300 cfs are required to pass Colorado pikeminnow over all the riflle transects,

assuming 27 cm is the minimum depth needed. We point out, however, that the transects were

randomly placed across the riflles and were not necessarily placed at the shallowest cross section.

In other words, minimum flows needed for passage might be >300 cfs. The shallowest riflle was

just below Taylor Draw Dam, and three others were between RM 20 and 48.

Uncertainties in Determining Flow Requirements for the White River.

This study had several shortcomings as a basis for determining future flow needs of

Colorado pikeminnow in the White River. As described in Model Critique, the precision of

estimates of habitat areas were only rough approximations; estimates.ofriflle wetted perimeter are

better, but simulated wetted perimeters at discharges <134 cfs are suspect because of

extrapolation problems. The use of habitat suitability curves developed from Yampa River data

and from White River data collected before Taylor Draw Dam closure are open to various

17