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Final Report 3-5 September 2000 Table 3.2.-Estimated depletions in the Green River system in 1998. Drainal!e Upper Green River (upstream of Greendale, Utah) Yampa River White River Duchesne River Price River San Rafael River Estimated 1998 DeDletion (1 000 000 m3)3 567 231 59 585 30 121 a Depletions were estimated by using the Colorado River Simulation System (CRSS) within the RiverWare modeling framework. Other approaches to calculating depletions may yield different results. snowpack and monthly runoff forecasts, an appropriate winter draw down is selected to avoid spills; it usually results in a minimum reservoir storage of approximately 987 million m3 at a reservoir surface elevation of 1,836 m. Minimum reservoir elevations are usually achieved by 1 April each year. In years when snowpack is greater than normal, releases are increased in middle and late winter and result in additional draw down. Following drawdown, attempts are made to refill the reservoir during spring runoff, with maximum reservoir levels usually occurring in late July each year. Releases during the remainder of the year are generally patterned to meet energy demands while meeting the constraints identified above. Peak demand for electric power occurs during summer (July through September) and winter (December through February). Water releases from the dam for power generation have ranged from about 23 to 130 m3/s. The maximum power-generating release3 is constrained by the size of the turbines, whereas the lower limit (23 m3/s) is set by an agreement with the State of Utah to maintain a high-quality trout fishery in dam tailwaters. An additional 113 m3/s of water can be released through two steel bypass tubes (56.5 m3/s each), and 793 m3/s can be discharged through the spillway tunnel, but water passing through these structures produces no electric power. Although power plant releases from the dam are capable of fluctuating from 23 to 130 m3/s to meet power commitments, actual daily operations are constrained to meet criteria presented in the 1992 Biological Opinion (USFWS 1992), usually by reducing the magnitude of (or eliminating) daily fluctuations in flow or by reducing the amount of time that peak releases are maintained. The history of Flaming Gorge Dam operations can be divided into five phases. In the first phase, from 1963 to 1966, Flaming Gorge Reservoir was filling with water, and flows downstream of the dam were much reduced (Smith and Green 1991). The first full year of normal operations 3In this report, maximum power plant capacity is reported as 130 m3/s, which is the typical historic maximum release value. With a recent system upgrade, power plant capacity releases up to 140 m3/s are possible but depend on reservoir water-surface elevation.