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.. 3.6.1 Flaming Gorge Monthly Operation Operating on a monthly basis, Reclamation informs Western of the amount of water in Flaming Gorge Reservoir which will be released. Western then schedules daily releases to maximize revenues and to balance the load on the transmission grid. A general rule is that peak electrical demand is highest during the summer air conditioning and the winter heating seasons. Peak summer months are July, August, and September and winter peak months are December, January, and February. These general demand patterns vary on a yearly basis, reflecting changes in the general climate and power use patterns. 3.6.2 Flaming Gorge Daily Operation On a daily basis, releases from the dam can fluctuate from a minimum of about 800 cfs to a maximum of about 4,200 cfs, solely from a power system need to provide adequate generation to meet power commitments. The lower releases usually occur at night and on Sunday while the higher releases occur during the daytime hours, thus matching power demand patterns. Changes from low to high flows occur at a specified "ramping rate", which during normal conditions is limited to about 300 cfs per minute and during emergency conditions to about 500 cfs per minute. In actual practice, this rate has been constrained to about 100 cfs per minute to limit the impacts of rapid river stage changes. Changes in releases at the darn, which can be quite dramatic, are more subdued when viewed by observers downstream. By the time the water reaches the confluence of the Yampa River, the stepped releases at the darn more resemble a normal (sinusoidal) hydrograph with no apparent ramping patterns being evident. Bank and pool storage and release accounts for the majority of the attenuation, between the darn and the confluence of the Yampa River. This resulting in minimum flows at the Yampa confluence that are higher than at the dam and maximum flows that are lower. The range of daily fluctuation is closely tied to the average daily release volume, which is in turn related to the monthly release volume specified by Reclamation. During low runoff years such as 1987 and 1988, low monthly volumes resulted in substantial periods of minimum releases while maximum releases were only about 2,000 cfs. During high runoff years extremely high monthly volumes dictated that the power plant.be operated at maximum capacity continuously with little or no daily fluctuation. During low water years releases are held at a minimum and little fluctuation occurs. In addition to this constant high power plant discharge, extreme runoff years sometimes also dictate the use of additional release capability through the jet tubes to the concrete spillway. The Operating Criteria instructs that these power plant bypasses be strictly minimized for reasons stated earlier. In order to comply with this provision, runoff forecasts and operational strategies are carefully prepared; winter and spring releases are often calculated solely as a function of changing snow pack and forecast conditions. 3-8