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Table S-7--Average Hydrology Scenario (Runoff Volume Exceeded 30 to 70% of the Time) 1992 Biological Opinion Action Peak Flow Determination The Biological Opinion calls for a peak release of 4,000 to 4,700 cfs for a duration of 1 to 6 weeks in all years. The intent of this peak release is to achieve a peak flow at Jensen, Utah, of 13,000 to 18,000 cfs for a period of 2 to 4 weeks in average years. Timing of the peak release would begin during the period from May 15 to June 1 so that the peak release would coincide with the peak flow of the Yampa River. Bypass releases, if necessary for hydrologic reasons, would be made before or during the Yampa River peak flow. Ramp Rate Determination The ascent rate would be limited to no more than 400 cfs per day. The decline rate would also be limited to 400 cfs per day. Base Flow Determination Summer flows, after the spring peak release, would be between 1,100 and 1,800 cfs at Jensen, Utah, for all years and would be reached by July 10 in average years. On September 15, if it is determined that the year was wetter than anticipated, the range of available target flows could be expanded to 1,100 to 2,400 cfs, if necessary. Hour-to-Hour Fluctuation Determination The flow at Jensen, Utah, would fluctuate no more than 12.5% of the daily average flow during the summer and fall period. Fluctuations during the winter period (November through February) would be moderated. Release Temperature Determination Releases during the period from July 1 to November 1 would be regulated to achieve the warmest possible temperatures, approaching 59 IF (15 °C). September 2000 Flow and Temperature Recommendations Peak Flow Determination In average years, the 2000 Flow and Temperature Recommendations call for a peak release that should achieve the following: The peak release should provide a peak flow in Reach 2 that exceeds 18,600 cfs in 1 out of 2 average years. In 1 out of 4 average years, the peak flow in Reach 2 should exceed 18,600 cfs for at least 2 weeks. In all average years, the peak flow in Reach 2 should exceed 8,300 cfs for at least 2 weeks. The minimum peak release from Flaming Gorge Dam should be 4,600 cfs. To target these requirements, the forecasted peak flow of the Yampa River would be supplemented by releases from Flaming Gorge Dam. The timing of the peak release should coincide with the peak and post-peak flows of the Yampa River. Ramp Rate Determination The ascent rate is not specified in the 2000 Flow and Temperature Recommendations. The decline rate for an average year should be 500 cfs per day or less. Base Flow Determination The base flow target at Jensen, Utah, should be between 1,500 cfs and 2,400 cfs during average years. Variability in flow around the established average base flow should be consistent with the variability that occurred in pre- dam flows. Accordingly, the average daily flow at Jensen, Utah, could fluctuate by 40% around the established average daily base flow target from August through November. From December through February, average daily the flow at Jensen, Utah, could fluctuate by 25% around the established average daily base flow target. Differences in average daily flows at Jensen, Utah, between consecutive days, and due strictly to reservoir operations, should not exceed 30/6. Hour-to-Hour Fluctuation Determination Flow variations resulting from hydropower generation at Flaming Gorge Dam should be limited to produce no more than a 0.1-meter (about 4 inches) stage change within a 24-hour period at the Jensen gauge. Release Temperature Determination Release temperatures should be regulated with the objective to meet or exceed water temperatures in upper Lodore Canyon of 64 IF (18 °C) for the first 2 to 5 weeks during the base flow period (mid-July to March 1) for average years. In addition to the above criteria, Green River temperatures at its confluence with the Yampa River should be no more than 9 IF (5 °C) colder than Yampa River temperatures during the summer base flow period. 5-30 400- Operation of Flaming Gorge Dam Draft EIS