WSP04165

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 6/1/2003
• Author: CDOW
• Title: Riverine Fish Flow Investigations 2003
• Water Supply Pro - Doc Type: Publication

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INTRODUCTION

Conservation and management of native species is now a major consideration
within the Colorado Division of Wildlife (CDOW). This is especially true for species
that are lisled as federally threaten or endangered. Four species of fish in the Colorado
River basin are listed as endangered by the U.S. Fish and Wildlife Service. The Upper
Colorado River Recovery Program was established to identify and resolve problems, so
these fish can eventually be down-listed (Wydoski and Hamill 1991). The state of
Colorado and the Recovery Program share the same goal of recovering the fish, but their
agencies may not share common strategies. A unifying approach for native fish
management objectives is to agree on the scientific validity of data involved in
identilication of limiting factors.

In Colorado State government instream flow protection for fish via water rights
has been a common practice in high elevation headwaters (Espregren 1998). Water rights
adjudication, however. has become a rigorous legal process for high profile wann water
rivers like the Colorado and Yampa Rivers where water is already highly over-
appropriated. In response, U. S. Fish and Wildlife Service (USFWS) conducted studies
for instream flow recommendations in regard to recovery of endangered fish species in
the IS-Mile Reach of the Colorado River (Osmundson et al. 1995) and the Yampa River
(Modde and Smith 1995). Modde et al. (1999) was a field-based study on the Yampa
River. also sponsored by the Recovery Program. Even though the intent of these flow
studies was the same, to determine stream flow requirements for endangered fish,
recommendations were based on vastly different methodologies.

The goal of this project was to develop biologically based instream flow
recommendations for the Colorado in the IS-Mile Reach and Yampa rivers based on
habitat and flow requirements for non-endangered native fish. The identification and
validation of flow needs for non-endangered native fish may assist in preventing listing
these species in the future. This data may also be of value to the Endangered Fish
Recovery Program by providing ancillary information concerning the overall fish
community and descriptions of physical habitat availability.

Typically CDOW uses the R2Cross method (Nehring 1979) or PHABSIM (Bovee
1982) for making instream flow recommendations for protecting cold water habitats.
However these two methods were not considered appropriate for the warm water sections
of the Colorado and Yampa Rivers given the elevated levels of biological, geomorphic
and social complexities for these rivers.

This study employed a Meso-Habitat approach that is similar in concept to
PHABSIM. PHABSIM is widely used in North America to quantify impacts of altered
flow regimes to habitat. PHABSIM consists of two modeling components. The
hydraulic component is a series of one-dimensional cross-sections that are linked to
produce a series ofrectangular cells that form a grid. Mean depth and velocity conditions
are calculated for each cell for a given flow. The biological component is a set of
suitability index curves for depth and velocity criteria that are used to rate micro-habitat