8170

• UCREFRP Catalog Number: 8170
• Author: Trammell, M. A., K. D. Christopherson, C. L. Rakowski, J. C. Schmidt, K. S. Day, C. Crosby and T. E. Chart.
• Title: Flaming Gorge Studies
• USFW Year: 1999.
• USFW - Doc Type: Assessment of Colorado Pikeminnow Nursery Habitat in the Green River.
• Copyright Material: NO

US Geolo ical Surve a e records show that rio d closure th Yam a River
g yg g ,p rto am e p
provided slightly less than half of the volume of water for the annual peak discharge. Since the
closure of Flaming Gorge Dam, the Yampa provides, on average, three-quarters of the volume of
water for the annual peak discharge (Figure 5).
Base Flows
The summer base flows for the period between 1970 and 1990 were much greater than
had occurred prior to construction of Flaming Gorge Dam. Since dam closure, September
typically has had the lowest mean monthly discharge of the year (Figure 5), although prior to
dam closure, December and January typically had the lowest monthly mean discharge of the
year. Prior to dam closure, September base flows were typically less than 40 m3/s (Figure 8).
After closure of Flaming Gorge Dam, base flows were as high as 85 m3/s and were never less
than 55 m3/s between 1970 and 1990 (Figure 7). After 1990 and the adoption of the Final
~! Biological Opinion for the Operation of Flaming Gorge, September base flows have been about
^ 42 m3/s. These September flows are more similar to pre-dam conditions.
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120
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~ 110
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~ 100
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70
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as
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~ 50
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40
vVi 30
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20
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1940 1950 1960 1970 1980 1990 2000
YEAR
Figure 8. Five-year moving average of September mean monthly discharge. Prior to dam
closure, the September mean discharge was typically the lowest of the year. While
the mean September discharges of the 1990s are closer to pre-dam levels than those of
the 1970s and 1980s, they still exceed the historic mean discharge for September.
Winter base flows (i.e., December, January, and February) have also increased since
closure of Flaming Gorge Dam (Figure 9). The average winter discharge has more than doubled
(Figure 5), and is greater than the current recommended summer dischazges, which is between 31
and 51 m3/s. The current flow recommendations establish target summer low flows, but allow a
much greater range, between 22.7 and 133.1 m3/s, for winter flows. Overwinter habitat stability
and availability are components of successful recruitment, but large discharge variations do not
contribute to habitat stability.
A-17