7762

• UCREFRP Catalog Number: 7762
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Annual Summary Report-1994, Effects of Flow Regulation and Ice Formation on Overwinter Nursery Habitat of Age-0 Colorado Squawfish in the Green River Below Flaming Gorge Dam.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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3.4 DATA COLLECTION AND STORAGE

Data collected in the field were recorded on a standardized data sheet. Data forms used and a list of field
codes are presented in Appendix A The data were stored in the database management system dBase IV 1.1™.

4.0 RIVER HYDROLOGY

Flow of the Green River through the study area was principally determined by releases from Flaming Gorge
Dam and tributary input from the Yampa River. Wintertime release volumes from Flaming Gorge Dam are
determined by water availability, storage and delivery, while daily fluctuations are determined by power
generation. The presence of the dam has had a significant effect on the yearly hydrograph by reducing spring
peaks and increasing fall and winter flows. This section provides an overview of the hydro graph during the
first year of this investigation (September 1993 - March 1994). A more detailed description of pre and post-
dam hydrology is included in the Synthesis of Winter Investil!ations of Endanl!ered Fish in the Green River
below Flaminl! Gorl!e Dam (Flaming Gorge Research Study #18-11).

4.1 MONTHLY FLOWS FROM FLAMING GORGE DAM

During the winter of 1993-94 (December through February), average monthly releases from the Flaming Gorge
Dam were 2,050 cfs with the highest average flow of 2370 cfs in December decreasing to a low of 1780 cfs in
February (Table 3).

Table 3.

Summary of average monthly releases (cfs) from Flaming Gorge Dam for December 1993
through February 1994.

MONTH MINIMUM MAXIMUM AVERAGE (S.D.)l
DECEMBER 1993 2020 2810 2370 (175)
JANUARY 1994 1640 2300 1960 (208)
FEBRUARY 1994 1550 2100 1780 (128)

I. S.D. = standard deviation of daily releases for month

4.2 DAILY FLOW FLUCTUATIONS FROM FLAMING GORGE DAM

Power generation from Flaming Gorge Dam can create substantial daily fluctuations in flow. Daily releases
can range from a minimum of 800 cfs to a maximum of 4,700 cfs. Maximum powerplant releases are
constrained by generator capacity and reservoir capacity. Minimum flow releases have been established by
UDWR to provide necessary flows for the tailwater trout fIShery. During typical power generation, lowest
releases are early morning (1:00 - 5:00 am), increasing abruptly around 6:00 am and again around 6:00 pm with
highest flows occurring approximately 8:00 pm. However daily fluctuation patterns can vary greatly due to
weekends, holidays or changing power needs.

Daily flow fluctuations were near maximum in January and February, 1994. Average daily fluctuations
(minimum to maximum) in January were approximately 1,000 cfs to 3,500 cfs. Average daily lows in February
were near 800 with highs of approximately 3,000 cfs. Figure 2 illustrates representative average and extreme
hourly releases from Flaming Gorge Dam for January and February of 1994.

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