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<br />" .~ <br /> <br />5 <br /> <br />September) and winter (December thraugh February). During these periods water <br />releases from Flaming Gorge Dam fluctuate within the operational constraints <br />.of the pawerplant (800-4,700 cfs). Flaming Gorge Reservoir results in an <br />estimated annual depletion of 78,300 acre-feet due to evaporation. <br /> <br />The mean annual flow of the Green River, near Jensen, Utah, is almost the same <br />now as prior to the construction of Flaming Gorge Dam, but the flows and <br />temperatures are significantly changed from historic patterns. In general, <br />spring peak flaws are much lower, while late summer and winter flows are <br />higher, than historic averages. Minor peaks in discharge .occur in summer and <br />winter corresponding to peak power demands, while base flows are generally <br />elevated during the remainder of the year to accommodate winter reservoir <br />drawdown and minimum flow agreements. <br /> <br />Flaming Garge .operations are within the general framework of the above' <br />criteria, but vary year to year based on hydrologic conditions. Historical <br />and post-Flaming Garge flows differ significantly (Figure 1). Historically, <br />flows in the river increased with the onset of snowmelt in March, peaked in <br />June, and remained high through July. The mean annual spring peak for the <br />historic period, measured at Greendale, was about 7,800 cfs. Following spring <br />runaff, flows declined to less than 1,000 cfs for the remainder of the year. <br />Variations of this pattern occurred during wet and dry historic periods. <br /> <br />Reservoir filling occurred from 1963-1966 with the first full year of <br />operation beginning in 1967. In 1979, Reclamation began releasing water <br />through the multilevel outlet structure which provided warmer water for fish. <br />Operations changed in 1985, when the Service and Reclamation signed an <br />"agreement" for protection of critical endangered fish nursery habitats <br />downstream of Jensen, Utah, and far other special releases associated with <br />study objectives contained in the interagency agreement (6-AA-40-04070). <br /> <br />BASIS FOR OPINION <br /> <br />The endangered Colorado squawfish, humpback chub, bony tail chub, and razarback <br />sucker inhabit the Green River. Occupied habitat currently extends from the <br />confluence with the Colorado River at river mile zero (0) upstream to near the <br />Willow Creek confluence (Swallow Canyon) at river mile 383.5. The main stem <br />Green River and its tributary, the Yampa, cantain the largest populations of <br />Colorado squawfish and razorback sucker known to exist in natural riverine <br />habitats. Humpback chub have a limited, discontinuous distribution in canyon- <br />bound habitats and persist in small numbers in Desolation and Whirlpool <br />Canyons. The bony tail chub is extremely rare throughaut the Upper Colorado <br />River Basin. <br />