WSP11586 - Laserfiche WebLink

Home Browse Search

001311 . . Draft Task 9 Technical Memorandum drafts of each reservoir over a consecutive I~ month period are 34,560 af, 10,700 af, and 50,210 af for Stagecoach, Steamboat and Elkhead, respectively. This analysis suggests that a single decree for this amount would be sufficient to cover the maximum draft on Stagecoach over the study period. Elkhead Reservoir, which is enlarged to 46,500 af would appear to require additional refill rights for a few thousand acre-feet in addition to a single annual filling. However, the average annual draft On Elkhead.at the 2040 demand level is 27,840 and the draft exceeds 46,500 af in only one year of the study period. There is an assumption in the model that Stagecoach, Steamboat and Elkhead Reservoir will be operated in the future under a transfer of a portion of Juniper Project water rights. Therefore, the contemplated draft of the Juniper rights was reduced by the modeled monthly combined drafts of Stagecoach, Steamboat and Elkhead. The combined draft of these reservoir is approximately 53,000 af per year. The modified average annual draft of the Juniper rights, as converted to an instream flow right at Juniper Canyon, is 808,000 af. Sizing of the Enlargements at Elkhead and Stagecoach Reservoir Several model runs were made to help identify the optimal size of Elkhead and Stagecoach Reservoirs under future demand conditions. In a first set of model runs, Stagecoach reservoir was modeled at 33,275 af and Elkhead Reservoir was modeled at several sizes between 13,700 af up to 52,000 af. Shortages to basin demands were examined and plotted against Elkhead Reservoir size. In a second set of model runs, Elkhead Reservoir was held constant at either 25,000 or 35,000 af and the size of Stagecoach Reservoir was varied. Again, shortages to basin demands were examined and plotted against Stagecoach Reservoir size. In all of these model runs, definition of the recreation pool at Elkhead Reservoir was based on the original 10 foot drawdown criteria. The result was an active enlargement pool which varied depending on the size of the enlargement. This had a direct affect on the amount of shortages experienced by demands. Figure 1 illustrates the relationship between demand shortages and Elkhead Reservoir size with and without the recreation pool constraint. Without the recreation pool, demand shortages are relatively small and increase only when the enlarged reservoir falls below 25,000 af. Many of the shortages at the larger sizes occur at demands which are above storage supplies. For the situation when the recreation pool is constrained during the summer months, shortages are significantly higher at all enlargement sizes but increase substantially below an enlargement to 35,000 af. Two series of models were run to help identify the optimal size of Stagecoach Reservoir. One series held Elkhead Reservoir capacity at 25,000 af while the second series modeled Elkhead at 35,000 af capacity. Figure 2 illustrates the relationship Stagecoach Reservoir capacity and demand shortages for the two different sizes of Elkhead Reservoir. Under both situations, shortages begin to increase significantly when the size of Stagecoach Reservoir is reduced below 40,000 af. These sizing studies were reviewed by the TSG at the October 16, 1992 meeting. Also reviewed at this meeting were the results of additional capacity evaluations at the Elkhead site. Based on these review discussions, the TSG determined that subsequent model runs should assume Elkhead enlargement to 46,500 af and Stagecoach enlargement to 52,000 af. 7 ;it. "'"