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

Yampa River discharge peaked. During summer, release levels were designed to maximize
nursery habitat for Colorado pikeminnow near and downstream of Jensen, Utah (Tyus and Karp
1991). To achieve the desired stable base flow of 51 m3/sec ( ± 12.5%, Pucherelli et al. 1990,
Tyus and Karp 1991, U. S. Fish and Wildlife Service 1992), releases were usually decreased to
as low as 22.3 m3/sec soon after prescribed high spring flows ended because Yampa River
discharge was usually high. Dam releases were increased later in summer after Yampa River
discharge declined and when Green River discharge at Jensen fell below target levels.
Water temperatures in the Green River upstream of the Yampa River in the period 1992
to 1996 showed a slightly warmer summer pattern than for the previous 1978 to 1991 period as
summer maxima typically peaked at about 18°C or less for a short period (Bestgen and Crist
2000). Summer discharge manipulations altered thermal regimes in the regulated reach because
flow level and water temperature were inversely correlated in the Green River downstream of
Flaming Gorge Dam (Vanicek et al. 1970, Bestgen and Crist 2000). This is because reservoir
releases that are cold relative to air temperature progressively warm via solar insolation
downstream from the dam, but warm faster in upstream reaches if flows are lower and slower.
Thus, under low drought flows, relatively warm water can be expected well upstream into
Browns Park if air temperatures are warm. Dynamics of flow and water temperatures and
regression models to predict downstream warming were discussed in detail in Bestgen and Crist
(2000) and Muth et al (2000). Because flows typically increased from Flaming Gorge Dam later
in summer during 1992 to 1996, maximum temperatures were sometimes achieved in late June
but often declined by mid July.
Flow and temperature regimes in the Green River downstream of Flaming Gorge Dam
since 1997 followed elements of both the 1992 Biological Opinion and newer proposed
recommendations. Higher spring releases were realized in 1997 and 1999 (Fig. 5), but spring
peaks during study years 2002 to 2004 were at or below power plant capacity (about 130 m3/sec,
Fig. 4). Compared to earlier post-regulation periods, in 1997 to 2004, and particularly for 2002
to 2004 study period (and in 2000 and 2001), base flows (August to February) were lower,
stable, and more closely approximated the historical hydrograph (Fig. 6, Table 1). Flows that
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