8188

• UCREFRP Catalog Number: 8188
• Author: Muth, R. T., et al.
• Title: Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Forge Dam.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Final Report

1-8

September 2000

some areas and, by stabilizing sediment deposits, gradually made the channel narrower and deeper,
with steep banks.

The Yampa River is the largest remaining essentially unregulated river in the upper
Colorado River basin, and its inflow into the Green River, 105 km downstream of Flaming Gorge
Dam, ameliorates some effects of dam operation on river flow, sediment load, and temperature. As
a result, endangered fishes in the Green River are now primarily restricted to sections downstream
of the Yampa River confluence (Figure 1.1), where they occupy habitats also used by 21 nonnative
fish species (Table 4.2). Holden (1980) concluded that flows from the Yampa River, especially
spring peak flows, were crucial to the maintenance of the Green Ri ver' s "large-river" characteristics
and, therefore, very important to maintaining suitable conditions in the Green River downstream of
the confluence. He speculated that loss of natural flows from tributaries of the Green River,
especially the Yampa River, could push the endangered fish species closer to extinction and
recommended against regulation of Yampa Ri ver flows (Holden 1980).

In 1990, the Service developed interim flow recommendations for the Yampa River
(USFWS 1990c) that were based on a review of existing biological data on endangered fishes in the
Green and Yampa rivers (Tyus and Karp 1989). Those interim recommendations called for
preservation of a natural seasonal pattern of flows in the Yampa River, including spring peak flows
that reflected the natural hydrologic regime and base flows equal to the 50% flow-exceedance level2
as measured at the U.S. Geological Survey (USGS) gage near Deerlodge Park. The recommended
interim flows followed a "stair-stepped" pattern that reflected the use of mean monthly flows for a
given period. Harvey et a1. (1993) identified the importance of the high spring peak flows in the
Yampa River for creating and maintaining conditions to promote spawning by Colorado pikeminnow
on cobble and gravel bars. Modde and Smith (1995) reexamined the interim recommendations in
light of additional studies conducted on endangered fishes in the Green and Yampa Rivers in order
to develop revised flow recommendations. They identified a need to maintain natural variability by
allowing flows to be driven by natural daily variability instead of average monthly flows. Additional
recommendations for August-October base flows needed by sub adult and adult Colorado
pikeminnow in the Yampa River were made by Modde et a1. (1999), in which a minimum target base
flow of about 3 m3/s was identified.

Flows in other tributaries, especially the Duchesne, White, Price, and San Rafael Rivers,
also are important to the maintenance of conditions in the Green River. The Service developed
preliminary flow recommendations for the Duchesne River (USFWS 1998b) that identified flows
for all months of the year under wet (25% exceedance), average (50% exceedance), and dry (75%
exceedance) hydrologic conditions. Additional research is underway to refine flow recommendations
for the Duchesne Ri ver. The Service currently is in the process of developing flow recommendations
for the White River, and it is anticipated that flow recommendations for other Green River tributaries
also will be developed in the future.

2Exceedance values refer to the percentage of recorded flows that are higher than that value. An exceedance
value is equivalent to 1 minus the percentile.