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<br />001268 <br /> <br />. <br /> <br />. <br /> <br />Draft Task 7 Technical Memorandum <br /> <br />contractual access to storage in Stagecoach, i.e. demands are shorted which have limited or no <br />storage contracts. <br /> <br />Reservoir Contents <br /> <br />Contents of Stagecoach Reservoir and Steamboat Lake under Scenario III cycle much in <br />the same manner as in the previous two scenarios (Figure 10). The average drawdown for <br />these two reservoirs was approximately 7,500 af and 3,100 af for Stagecoach and Steamboat, <br />respectively. Drawdown in Steamboat Lake was due only to releases from the USFWS to <br />supplement flows for fish in Yampa River. Stagecoach was drawn down approximately 15,000 <br />af for several months during the 1934 drought period but the recreation pool constraint of <br />16,400 af was never violated. <br /> <br />There was considerable cycling in contents of Elkhead Reservoir in this scenario. This <br />was in large part due to the use of the Elkhead enlargement pool by basin demands that have <br />no specific storage contracts. Drawdown in Elkhead Reservoir averaged 14,000 af over the <br />study period with the maximum drawdown occurring in the months of January, February and <br />March. In the model run with the recreation pool constraint lifted at Elkhead, the reservoir <br />was occasionally drawn down to the pre-enlargement minimum pool (approximately 3,722 at). <br />This occurs only in the driest years of the study period. <br /> <br />Under 2040-level demand conditions the maximum drawdown in Elkhead Reservoir was <br />approximately 32,500 af and occurred in the months of February and March (Figure 10). <br />During the summer months Elkhead was occasionally at or below the minimum pool of 39,500 <br />af. Although the model allowed no demands to be served out of Elkhead once the minimum <br />pool was reached, the reservoir could be drawn down further as a result of low inflows and <br />evaporative losses. In several instances, Elkhead was already below the summer recreation <br />pool target during the spring months. The constraint on the recreation pool does not help the <br />reservoir fill after severe winter and spring draw downs; it only prohibits deliveries once the <br />reservoir is at or below the minimum level. <br /> <br />When the recreation pool constraint was lifted at Elkhead Reservoir there were several <br />instances when the modeled reservoir contents were drawn well below 39,500 af in the summer <br />months. However, the reservoir tended to refill quickly and does not stay below the original <br />recreation pool level (39,500 at) for more than a few months at a time. <br /> <br />SCENARIO IV. ENLARGEMENT OF ELKHEAD AND STAGECOACH <br />RESERVOIRS <br /> <br />Key Assumptions of the Scenario <br /> <br />Model runs in Scenario IV included both an enlarged Elkhead Reservoir and an enlarged <br />Stagecoach Reservoir. Elkhead Reservoir was configured in exactly the same way as in <br />Scenario III. Stagecoach Reservoir was enlarged to a capacity of 52,000 af. This represents <br />an increase of approximately 18,275 af over existing conditions and is the maximum reasonable <br />enlargement identified through Task 5 of the Feasibility Study. The enlargement pool at <br />Stagecoach was modeled in a manner similar to the Elkhead enlargement in that the <br />enlargement pool may be used by all demands and was allocated on a first come, first served <br />basis. Demands must first use all of their existing storage contracts prior to receiving <br />deliveries out of the enlargement pools. <br /> <br />13 <br />