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<br />" <br /> <br />. <br /> <br />. <br /> <br />001264 <br />Draft Task 7 Technical Memorandum <br /> <br />Steamboat and Hayden may also access the 4,000 af mixed used pool at Stagecoach Reservoir <br />if the M&I pool has been depleted. <br /> <br />Reservoir storage accessed by thermal-electric demands has been prioritized in the model <br />over the three existing reservoirs. Craig Station demands were met first out of the 8,310 af <br />pool in Elkhead Reservoir. Any remaining unsatisfied Craig Station demand, as well as the <br />entire Hayden Station demand were then met from the 9,000 af pool in Stagecoach Reservoir. <br />If this is insufficient, the 5,000 af pool in Steamboat Lake will be used to meet the demands of <br />the Hayden Station. Finally, if thermal-electric demands were still not met, the 4,000 af mixed <br />use pool in Stagecoach Reservoir can be accessed. <br /> <br />Future agricultural demands and the proposed coal gasification plant near Craig do not <br />have access to existing reservoir storage water in the model. <br /> <br />Elkhead Reservoir Outlet Capacity <br /> <br />The present capacity of the outlet of Elkhead Reservoir is 165 cfs. To meet dam safety <br />requirements, Elkhead Dam (if not enlarged) will undergo major modifications in the near <br />future. These modifications will likely include enlargement of the outlet capacity to at least <br />250 cfs. There are currently no power generating facilities at the dam. Preliminary model <br />results indicated that predicted shortages to demands frequently occur as a result of the outlet <br />constraint and the inability to release more water to downstream users. The sensitivity of <br />predicted demand shortages was evaluated by enlarging the outlet to 800 cfs and comparing <br />with results from original model runs. The results of this sensitivity test indicated that a <br />, substantial number of shortages were eliminated by an outlet enlargement but that shortages <br />still occur in selected years. The maximum conveyance of the Elkhead Creek channel below <br />the reservoir has been estimated at 250 cfs; flows above this level have historically resulted in <br />minor flooding of farmlands. Scenario I model assumptions reflect a 250 cfs Elkhead outlet. <br /> <br />Results of Scenario I <br /> <br />Demand Shortages <br /> <br />In Scenario I, shortages to existing senior demands averaged 18 af per year (Table 3). <br />These generally were shortages which could not be mitigated because the modeled shortages <br />were located where it is impossible to increase the available supply (e.g., on small tributaries <br />with no storage). Occasional shortages also occurred due to capacity constraints of reservoir <br />outlet works. Demand shortages generally occurred only in the driest years of the study <br />period. <br /> <br />Shortages to existing junior demands average 294 af per year (Table 3). The majority of <br />these shortages occur to a demands representing junior agricultural rights above Stagecoach <br />Reservoir which cannot be serviced by modeled storage projects. Several small existing <br />reservoir in the upper Yampa basin were not explicitly modeled. These shortages occur only <br />in a few months of the study period when there was insufficient divertible supply. ' Shortages <br />to other junior demands below Stagecoach Reservoir occurred only in the dry years of 1934, <br />1960 and 1977. <br /> <br />Modeled demand shortages to near-term (20l5-level) demands averaged SO af per year. <br />These shortages occurred at Demands #31 and #32 which represented future Craig area power <br />and agricultural demands, respectively. Shortages to Craig area power demands only occurred <br /> <br />9 <br /> <br />4-\ <br />