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C. Yield Analysis <br />Separate spreadsheet models were developed for the large reservoir (Alignment 1) and the smaller <br />reservoir (Alignment 2). Unique characteristics of the spreadsheets were the manner in which annual <br />demand was assigned to different uses and distributed to months, as described above; and the area- <br />capacity tables differed because of the different reservoir alignments. Other than that the models were <br />very similar. <br />For each month of the 31-year study period, the reservoir operations spreadsheets calculate deliveries to <br />the reservoir, releases from the reservoir, and evaporation, and then update the storage content. One <br />column is devoted to shortages to demand. The time series of available flow at the river headgate, <br />described in Section II.A, is loaded into the sheet, and is the same for all configurations of reservoir, <br />diversion capacity, and annual demand. The user may specify diversion capacity and annual demand. <br />The models distribute the annual demand to monthly as described in Section iV.B, including, for the <br />Alignment l reservoir, fish releases in dry years but not wet years. <br />The procedure to identify firm yield was to select a diversion capacity and annual demand, and check for <br />any shortages throughout the 31 years. The annual demand was raised or lowered until there was a <br />single month with shortages. When annual demand was lowered by 500 ac-ft, no monthly shortages <br />existed. The diversion capacity was then reduced successively to determine whether the firm yield could <br />be achieved with a smaller conveyance structure. <br />Results — Larger Reservoir (Alignment 1) <br />Figure 10 and Table 6 show results for the 154,500-af reservoir impounded by dam Alignment <br />1: <br />42 <br />AECOM <br />2/22/10 <br />