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e e e In addition to institutional constraints, economics also constrain the use of the jet-tubes and spillway. Any water that bypasses the generators represents a significant loss of revenue, likewise with the spillway. Use of the spill- way also has a further disadvantage in that physical damage to the spillway and downstream access roads are incurred and must be repaired. These again are economic costs which can be valued and assigned to different operational objectives. 3.5.4 Environmental Constraints Environmental constraints are those which in some way restrict the operation of the dam to limit adverse impacts to the natural resources of the Green River. Examples of current constraints are the minimum flow for the trout fishery, moderate power plant ramping rates, the installation of the multi- level intake structure to increase the temperature of the releases, and the avoidance of spills to limit the erosion and danger of extreme releases. Environmental constraints are closely linked to economic constraints, since in most cases maximizing one reduces the other. 3.6 Flaming Gorge Construction and Hydrology Advanced planning for Flaming Gorge Reservoir began in the early 1950's, and a gage was installed at the present dam site in 1951 and hydrological data collection continues to the present. Dam construction began in 1956 and was completed in 1964. Filling of the reservoir initiated in 1962 and continuing through 1966. Full operation of the facility began in 1967 and has continued under a number of different operational criteria. The average unregulated inflow to Flaming Gorge Dam is about 1.7 MAF which represents 45 percent of the storage capacity. The great majority of this inflow comes in the April-July period in the form of snowmelt runoff from the Wind River Mountains and the Uinta Mountains. The reservoir formed by the dam has a surface area of 42,000 acres and is 91 miles long, extending to within 5 miles of Green River, Wyoming. The reservoir live storage capacity is 3.75 MAF, 12 percent of the total CRSP live storage of 31.4 MAF. To accommodate inflow, Flaming Gorge Reservoir is annually drawn down about 800,000 acre-feet to elevation 6,020 feet. Winter and spring releases are adjusted according to the forecasted spring inflow to fill the reservoir during the latter part of the spring runoff. The minimum reservoir level occurs in March while the maximum level usually occurs in July. During the remainder of the year, releases are patterned, when possible, to match monthly electrical energy demand. Historically, Flaming Gorge has been maintained as full as possible to ensure that compact requirements can be met. Within this constraint, Flaming Gorge is primarily operated for power generation, but as the Upper Basin States develop their compact entitlement scheduled monthly releases could become more important. Currently no firm schedule of monthly releases from Flaming Gorge exists, principally due to the lack of water development along the Green River below the dam. Flaming Gorge along with other upper basin CRSP reservoirs have remained "on call" to provide water to lake Powell, eventually supplying water to be delivered to the lower Basin. Throughout Flaming Gorges operating history the Upper Colorado Basin States have indicated a desire to keep the reservoirs full. After major flood events in 1983 and 1984 this objective was currently tempered by spill avoidance criteria designed to avoid power plant bypasses (spills) which not only forgo power revenue but also can produce great environmental damage downstream of the dams. 3-6