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'001.261 . . Draft Task 7 Technical Memorandum flow right. All basin demands have access to water in the enlargement pool. Demands with existing contract storage must use their contract water prior to taking water deliveries out of the enlargement pool. Modeled releases from the enlarged Elkhead Reservoir to satisfy demands were assumed to be restricted by a 39,500 af minimum pool during the summer months, June, July and August. This represents a maximum allowable decrease in the surface water elevation of 10 feet during the recreation season. This feature of the model was designed to reflect basin interests to maximize recreational potential of the reservoir. As this operational rule was implemented in the model, water held in Elkhead Reservoir contract accounts may be transferred over to the minimum pool during summer months. This occasionally results in shortages to demands which might otherwise have been satisfied if there were no minimum pool constraint. Shortages which occur as a result of this transfer between accounts were relatively small and infrequent. To assess the impact of the Elkhead recreation pool constraint on demand deliveries a second version of this seenario was run with the constraint removed. Several demand shortages were eliminated when the recreation pool constraint was removed, however some shortages remain. The recreation pool constraint was included in all model results presented in this memorandum, however the notion of allowing access to the recreation pool in times of drought is a consideration. As in previous scenarios, modeled agricultural demands and the proposed coal gasification plant are assumed to not have access to existing storage. These demands, however, may be served by water out of the enlargement pool at Elkhead Reservoir. Results of Scenario Demand Shortages Scenario III model results indicated that shortages to existing senior demands were essentially unchanged in this scenario from the previous two scenarios and average 18 af per year over the study period (fable 5). Modeled demand shortages occurred either above Stagecoach Reservoir or on tributaries where deliveries of stored water could not be made. Explicitly modeled existing junior demands were shorted an average of 1,937 afper year. The majority of these shortages occurred above the confluence of Elkhead Creek and cannot be mitigated directly by releases out of Elkhead Reservoir. Demands upstream of Elkhead Reservoir may benefit from reservoir releases if physical supply in the Yampa River allows for an exchange. Shortages to future demands for 2015-level and 2040-level averaged 129 and 4,385 af per year, respectively (Figure 9). Because the basin model allows reservoirs to fill ahead of future demands, the additional storage space in Elkhead Reservoir occasionally results in greater monthly shortages to future demands than were observed in Scenario II. On the average, however, the additional storage space in Elkhead serves to mitigate many of the shortages experienced by future demands under Scenario II. Many of the shortages to future level demands were located in the Craig area and were the result of deliveries out of Elkhead Reservoir being limited by the 39,500 af summer recreation pool. When the Elkhead recreation pool constraint was lifted, shortages to the 2015- and 2040-level demands were reduced to 0 af and 295 af, respectively. Minor shortages occur due to outlet capacities at Elkhead and Stagecoach Reservoir and limitations on 12 it 0:..