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<br />,)~i~ <br />'...ii", <br /> <br />i;~ <br />.:<:~j <br /> <br />4 <br /> <br />Construction of the dam and powerplant began in 1956 and was completed in <br />1964. Fill ing of the reservoir began in November of 1962 'and continued <br />through 1966. Full operation of the facil ity began in 1967. Reservoir <br />releases through the powerplant range from 800 to 4,700 cubic feet per second <br />(cfs). Maximum powerplant releases are constrained by generator output and <br />reservoir elevation; while minimum releases are constrained by an agreement <br />with the Utah Division of Wildlife Resources which provides for a minimum flow <br />of 800 cfs to maintain the tailwater trout fishery. Additionally, the dam has <br />the capacity to release up to 4,000 cfs through two river outlets (jet tubes) <br />and an additional 28,800 cfs through the spillway. <br /> <br />OPERATION <br /> <br />Existing and proposed future operational criteria for Flaming Gorge Dam and <br />reservoir provide for a full reservoir while maximizing power revenue and <br />avoiding the use of the jet tubes and/or spillway. Depending on snow-pack and <br />monthly forecasting, an appropriate winter drawdown to avoid spills results in <br />minimum reservoir storage of approximately 800,000 acre-feet at 6,020 feet in <br />elevation which usually occurs in March. Attempts are made to re-fill the <br />reservoir during spring runoff, and maximum levels usually occur in July. <br />Releases during the remainder of the year are patterned to meet energy <br />demands. Peak electrical power demand occurs during summer (July through <br />September) and winter (December through February). During these periods water <br />releases from Flaming Gorge Dam fluctuate within the operational constraints <br />of the powerplant (800-4,700 cfs). <br /> <br />The mean annual flow of the Green River is almost the same now as prior to the <br />construction of Flaming Gorge Dam, but the annual distribution hydrograph and <br />temperature regime are significantly different. In general, spring peaks are <br />much lower while late summer and winter flows are higher than historic <br />averages. Minor peaks in discharge occur in summer and winter corresponding <br />to peak power demands, while baseflows are generally elevated during the <br />remainder of the year to accommodate winter reservoir drawdown and minimum <br />flow agreements. <br /> <br />Fl~ming Gorge operations are within the general framework of the above <br />criteria, but there are four distinctly different operational periods: <br />historic, filling period, pre multilevel outlet, and post multilevel outlet. <br />Historical and post-Flaming Gorge hydrographs at Greendale, Utah (directly <br />below the dam), at Jensen, Utah, and at Green River, Utah are significantly <br />different (Figure 1). In addition, certain changes in the Green River <br />hydrograph for various hydrologic periods associated with preoperation and <br />postoperation. The predam hydrograph of the Green River is represented in <br />Figure 2. Flows in the river increased with the onset of snowmelt in March, <br />peaked in June, and remained high through July. The mean annual spring peak <br />for the predam period, measured at Greendale, was about 7,800 cfs. Following <br />spring runoff, flows declined to less than 1,000 cfs for the remainder of the <br />year. Variations of this scenario occurred during wet and dry historic <br />periods. <br />