9374

• UCREFRP Catalog Number: 9374
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Effects of Flow Regulation and Ice Processes on Overwinter Nursery Habitat of Age-0 Colorado Pikeminnow in the Green River Below Flaming Gorge Dam.
• USFW Year: 1999.
• USFW - Doc Type: FG-10,
• Copyright Material: NO

Dinosaur National Monument, to the Ouray Bridge (RK 399) near Ouray, Utah, and waas divided
into the following three reaches, based on channel morphology and projected influence of stage
changes from fluctuating dam releases on ice development (Valdez and Masslich 1989):

1. Reach 1 began 122 km downstream from Flaming Gorge Dam and extended from
Island Park (RK 536) to Rainbow Park (RK 525). This reach was the closest to the
dam and most affected by vertical stage changes from fluctuating dam releases.

2. Reach 2 began 145 km downstream from the dam and extended from Split Mountain
(RK 513) to Bonanza Bridge (RK 467). This reach was moderately affected by
fluctuating releases.

3. Reach 3 began 191 km downstream from the dam and extended from Bonanza
Bridge to Ouray (RK 399). This lower reach was far enough downstream from the
dam to be unaffected by stage changes from fluctuating dam releases.

METHODS

Three scheduled 5-day field trips, including one in autumn and two in winter, were conducted
during each of the winters of 1993-94 and 1994-95 (Table 1). The autumn trip (i.e., October) was
conducted to reconnaissance and map backwaters after initiation of winter releases from the dam and
prior to ice development. The two subsequent winter trips (i.e., January, February) were conducted
to remap backwaters and to evaluate ice conditions. This study consisted entirely of physical and
chemical habitat assessment and did not involve fish sampling. In addition to the scheduled field
trips. short-term ground and aerial reconnaissance trips were conducted in 1993-94 to evaluate the
progress of ice development and. breakup, and to determine the most appropriate time for field
measurements. Additional monitoring of ice conditions was performed by personnel ofUDWR,
Northeast Regional Office in Vernal, Utah.

Special releases were made from Flaming Gorge Dam during this 2-year study to test the
effect of flow volume, flow magnitude, and range of flow fluctuation on ice processes in backwaters
of the Green River. In 1993-94, high releases were made with maximum allowable fluctuations, and
in 1994-95, low relatively steady releases were made. Special dam releases were made in
cooperation with Bureau of Reclamation (Reclamation) and Western Area Power Administration.
I Iourly releases from Flaming Gorge Dam were determined by converting megawatts of power to
cubic feet per second, based on data and conversion factors provided by Reclamation. Data on mean
daily flows, water temperature, and volume for the Green River were obtained from the U.S.
Geological Survey (USGS) stream gages located at Greendale, Utah (station 09234500) and near
.Jensen. Utah (station 09261000). The Greendale gage is located 0.8 km downstream from the dam
and the Jensen gage is located 174 km downstream from the dam and below the inflow of several
tributaries, including the Yampa River. Air temperature data were obtained from the National
Oceanic and Atmospheric Administration (NOAA) weather station near Jensen. Historic flow and
temperature data were summarized from USGS data compiled in the GeoSelect Colorado River
Database (Hydrosphere Data Products, Inc., Denver, Colorado).

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