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<br />otn269 <br /> <br />. <br /> <br />. <br /> <br />Draft Task 7 Technical Memorandum <br /> <br />Protocols to access the various reservoir storage pools was similar to the protocols <br />described for Scenario III. In Scenario IV, the model serves demands out of the Elkhead <br />enlargement pool prior to taking water from the Stagecoach enlargement pool. <br /> <br />Results of Scenario <br /> <br />Demand Shortages <br /> <br />Shortages to existing senior demands averaged 18 af over the 53 year study period <br />(Table 6). Explicitly modeled existing junior demands were shorted an average of 40 af per <br />year. The shortages to explicitly modeled junior demands occur above Stagecoach Reservoir <br />and cannot be mitigated through reservoir releases. <br /> <br />The enlargement pools at Elkhead and Stagecoach Reservoirs have a 1954 priority to <br />reflect transfer of a portion of the Juniper rights. In several instances demands were shorted in <br />this scenario which were not shorted without reservoir enlargements. This was because with <br />smaller reservoirs, modeled demands were occasionally met with water that spills. A larger <br />reservoir can reduce the frequency and amounts of spillage. These shortages occur only to <br />demands that are junior to 1954. <br /> <br />Shortages to future level demands averaged 0 af and 189 af per year under the 2015- <br />level and 2040-level demands, respectively (Figure 11). It should be noted here that some <br />existing senior demands experienced shortages when future junior demands did not because of <br />one of two reasons: 1) an insufficient physical water supply and the inability to serve the <br />demands through reservoir releases or 2) the fact that several senior demands have access to <br />contracts to stored water. Most of the shortages occurring in previous model scenarios were <br />eliminated through releases out of Stagecoach Reservoir. Modeled releases from the <br />Stagecoach enlargement pool were made to all demands in the model including those located <br />outside of the boundaries of the Upper Yampa River Water Conservancy District. <br /> <br />Reservoir Contents <br /> <br />In Scenario IV, aside from the seasonal operations for drawdown (Stagecoach Reservoir) <br />and releases to augment Yampa River fish flows (from Steamboat Lake) storage levels in <br />Steamboat Lake and Stagecoach Reservoir remained near full throughout most of the study <br />period (Figure 12). The majority of the demands requiring storage releases were met out of <br />the Elkhead Reservoir enlargement. The Elkhead enlargement was modeled with a lower <br />priority than the Stagecoach enlargement, therefore water was withdrawn from Elkhead first. <br />Releases from Stagecoach Reservoir occurred only when there were outlet works capacity <br />constraints on Elkhead Reservoir releases. <br /> <br />Drawdown of storage at Elkhead Reservoir averaged 14,000 af with the maximum <br />drawdown occurring during the months of January and February. Elkhead was drawn down <br />nearly 32,000 af during several months of the driest years of the study period. There was <br />minimal use of the Stagecoach enlargement pool. The additional supply from Stagecoach <br />eliminated the shortages evident in Scenario III and could reduce some of the pressure on <br />Elkhead Reservoir to make releases. Except for releases from the USFWS pool, releases from <br />Steamboat Lake occur only in a few months of the driest years and the reservoir remains <br />virtually full throughout the study period. Draw down impacts to all reservoirs in this scenario <br />might be more evenly distributed through more coordinated management efforts, especially <br />between use of Stagecoach and Elkhead reservoirs. <br /> <br />14 <br /> <br />l> <br />