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<br />c.':> <br /> <br />'.....J_ <br /> <br />N <br />.." <br />~ <br />~ <br /> <br />"''"'" , <br /> <br />, <br />, <br /> <br />.' , <br /> <br />. <br /> <br />reach maximum. The CRSS model does not model the call situation but rather <br />it indicates the quantity of the call by the amount it shorts the Lower <br />Basin delivery. Appendix III shows the results of the analysis. Using <br />these data, a frequency analysis was made which demonstrates both severity <br />and frequency of a call on the river at a demand level of 6.1 MAF. <br /> <br />The results indicate that the frequency of a call of 100,000 acre feet or <br />less is about 0.75 percent while that of a call over 2 MAF is less than 0.3 <br />percent. This is shown on an incremental basis in Figure 2 and on a <br />cumulative basis in Figure 3. A general conclusion of this analysis is <br />that calls on the river are likely to occur only very rarely even at a 6.1 <br />MAF demand level, but their effects could have significant impact to the <br />Upper Basin and their magnitude could range to over 100 percent of Upper <br />Basin depletion. Cursory examination of demands less than 6.1 MAF <br />indicates that both frequency and magnitude of calls on the river diminish <br />rapidly below this demand level. <br /> <br />6. Other Considerations - Changes in Assumptions <br /> <br />To obtain a wider range of yield analysis results, various changes in basic <br />a~sumptions were made and the corresponding results arrayed with previous <br />work. In particular, the use of inactive storage pools and a change in <br />minimum delivery to the Lower Basin were examined in regards to the effects <br />on Upper Basin yield. In the mass balance analysis discussed above, the <br />total amount of system storage used during the drawdown period as <br />determined from the use of CRSS was 24.762 MAF. There remained in inactive <br />storage and minimum power pools another 3.012 MAF. If it is assumed that <br />this entire amount is available for use and that the length of the drawdown <br />period would be the same as previously determined, the amount of storage <br />adjusted for use in a mass balance analysis using annual data would be: <br /> <br />[(24.762 + 3.0l2)x25/25.5833] - 4.00 = 23.141 MAF. <br /> <br />utilizing this value in the mass balance procedure along with a minimum <br />release of 8.23 MAF at Glen Canyon produces a firm yield (no shortages) of <br />5.67 MAF for the Upper Basin. The results of additional analysis which <br />relate yield to basin wide shortages and the probability of meeting a yield <br />given a particular shortage are shown in Figure 4. Because the data are <br />somewhat limited, it should be understood that these curves are only <br />approximate and only give an indication as to the probabilities involved. <br /> <br />9 <br />