9556 - Laserfiche WebLink

Home Browse Search

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 2005 and 2006, spring releases were higher than powerplant capacity in each year, 195 m'/sec in 2005 and 173 m'/sec in 2006 (Fig. 4). Higher flows were released mostly to enhance peaks of the Green River downstream of Jensen, Utah, to facilitate estimation of entrainment rates of buoyant beads and razorback sucker larvae into flood plain wetlands. Base flows were relatively high at about 41.6 m'/sec in 2005 but in 2006 were comparable to 2002 and 2003 at about 25 m'/sec (Fig. 7). 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 (Fig. 2). In 1992 to 1996, flow peaks were lower than historically, had higher base flows, and were of moderate duration. In 2002 to 2006 drought years, flow peaks were low (slightly higher in 2005 and 2006), had very limited duration even compared to 1992- 1996, and declined to base flow relatively early in summer. Additionally, timing of peak flow 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 and the new Flaming Gorge Dam flow recommendations (Muth et al. 2000, Record of Decision, U. S. Bureau of Reclamation, 2006). As a result of relatively low base flows 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), and that trend continued in 2005 and 2006 (Fig. 8). Summer water temperatures were particularly warm in the Green River upstream of the Yampa River in 2002 and 2006, when daytime highs reached 25°C in late July, and matched the summer maxima observed in the limited 1957 to 1962 historical period. In years 2005 and 2006, and perhaps portions of 2004, it appears that penstock level at Flaming Gorge Dam was manipulated to achieve release temperatures below the dam as high as 15°C in summer (in part, Fig. 9), whereas in 2002 and 2003, penstock levels were manipulated to limit releases to a temperature of 13°C or sometimes 17