9596

• UCREFRP Catalog Number: 9596
• Author: Ayers Associates.
• Title: Yampa River Basin Research Final Synthesis Report.
• USFW Year: 1999.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

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2.3. Previous Studies

In 1990, the CRWCD initiated a study to consider the effect of the Juniper water right on instream
flows and other water uses. The Yampa Steering Committee was set up to guide the study. The
first Phase of this study was to estimate future demands for water in the basin, identify potential
storage opportunities, and determine the requirements for stored water in order to satisfy Juniper
Project demands. This study treated the demands for the Juniper right as an instream flow.
Hydrosphere (1993) summarized the results of this study.

In the second phase of the study, Hydrosphere (1995a) simulated the use-of flow targets for the
Yampa River, rather than using the Juniper water rights. This study further looked at the
feasibility of enlarging Elkhead reservoir. The flow targets used for this study were preliminary
targets proposed by the USFWS.

Since that time, there have been several refinements of flow targets as discussed in Chapter 3 of
this report. Hydrosphere completed additional studies, which are summarized in Appendix A of
this report. These studies have looked at flows recommended by the USFWS, instream flow
filings by the CWCB and various alternative target flows.

Hydrosphere (1995) also completed a Reconnaissance Evaluation of Yampa River Diversion
Structures. There are hundreds of diversion structures along the Yampa used mostly to divert
water for irrigation. At the time of the study, these structures were believed to inhibit migration of
the Colorado pikeminnow and other endangered fish. The objectives of the study were to:

1. develop an inventory of problematic mainstem Yampa diversion structures in river
reaches where endangered fish species are likely to occur;

2. make a reconnaissance-level evaluation of the potential effects of such structures on
flow conditions, fish passage, and aquatic and riparian habitats;

3. make preliminary recommendations concerning the structures thought to be most
problematic;

4. describe, in a preliminary way, potential alternatives to reduce any adverse effects of
these structures or their maintenance on endangered fishes.

The study found that the Maybe" Canal and K. Diamond/Patrick Sweeney Ditch diversion
structures may represent significant obstacles to fish passage and recommended that a
biological study, involving radio telemetry, be considered for these two structures (Hydrosphere
1995b). Subsequent studies by Miller and Rees (1997) and Modde et al. (1999) found that the
existing structures do not appear to pose a challenge to the migration of Colorado pikeminnow.
Colorado pikeminnow typically migrate after spawning during periods of higher flows, when the
existing man-made and natural obstacles do not impede fish passage. During lower flows, when
these structures present potential barriers to fish passage, pikeminnow typically are less mobile.
However, if these structures were modified, fish passa~ could be impeded at higher flows.
Replacing a sloping rock structure with a vertical concrete structure, for example, could preclude
fish from migrating above the structure at any flow.

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