9549

• UCREFRP Catalog Number: 9549
• Author: Bestgen, K. R., K. A. Zelasko, R. I. Compton and T. Chart.
• Title: Response of the Green River Fish Community to Changes in Flow Temperature Regimes from Flaming Gorge Dam since 1996 based on sampling conducted from 2002 to 2004.
• USFW Year: 2006.
• USFW - Doc Type: 115,
• Copyright Material: NO

resulted from the 1992 Opinion recommendations were more variable. For example, summer
base flows more than doubled from about 23 m'/sec in June to nearly 50 m'/sec in August in the
low flow year 1994.
In all periods, regulated flows showed large differences in hydrograph shape. Historical
flows had a longer duration peak, increased to peak and declined from peak more gradually, and
base flows were lower. Additionally, timing of the peak from the regulated Green River
upstream of the Yampa River exhibited peak flows several weeks earlier than was historically
seen, peaking now in late May rather than mid or late June (Fig. 2), as dictated by the 1992
Biological Opinion.
As a result of relatively low baseflows in 1997 to 2004, summer water temperatures in
Lodore Canyon increased to levels likely not observed since Flaming Gorge Reservoir filled in
1967 (Fig. 3). Summer water temperatures were particularly warm in the Green River upstream
of the Yampa River in the 2002 to 2004 study period and matched the summer maxima observed
in the limited 1957 to 1962 historical period (Fig. 7). Water temperatures were particularly
warm during summer 2002, when daytime highs reached 25°C in late July. Only on four days in
the 2002 to 2004 period were water temperatures in the Green River more than 5°C different
than the Yampa River, and those were all in 2002 in late August (Table 2).
Effects of Flaming Gorge Dam on Green River discharge and temperature patterns,
Whirlpool Canyon.-Annual peak flows in the pre-impoundment period (1946-1962) showed a
typical dome-shaped hydrograph, with low late summer, autumn, winter, and early spring base
flows, rising to a peak in later spring and early summer (Fig. 8). Post-Flaming Gorge peak flows
in the 1992 to 1996 and 1997 to 2004 periods were lower than historical, from a standpoint of
mean daily annual flow, peak flow, and maximum May-June average flows (Table 1). Base
flows in the period August to February were typically lower in the pre-impoundment period than
post. Mean July-August summer base flows were lower in 1992 to 1996 than historical flows,
and mean July-August base flows in the 1997 to 2004 period were the lowest of all three periods.
Peak flows for the Green River in Whirlpool Canyon during study years 2002 and 2004
showed a lower and earlier peak than the historical average condition, while the 2003 peak flow
17