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<br />C:J <br />':J <br />t~ <br />~ ~, <br />w <br />Q <br /> <br />199 <br /> <br />Figure 6.11 displays similar information on 10-year average <br /> <br />Powell discharge when the maximum allowed Powell storage is increased <br /> <br />to SPM = 27 MAF. For this case the probability of failing to meet <br /> <br /> <br />the specified discharge is lower, due to the greater storage provided. <br /> <br />An increase in the probability of failure is observed following inc1u- <br /> <br />sion of the eighth simulation. In order to determine whether the ex- <br /> <br />treme conditions encountered during that particular simulation were <br /> <br />representative of conditions which could be expected in one out of <br /> <br />every ten simulations, an additional ten simulations were performed <br /> <br />using new streamflow sequences. None of the additional simulations <br /> <br />produced the large number of failures observed in simulation number <br /> <br />eight, above. <br /> <br />Figures 6.10 and 6.11 show that extreme points in the probability <br /> <br />distribution of reservoir discharge fail to converge to clearly dis- <br /> <br />cernib1e values when 2000 observations (years) are included in their <br /> <br />determination. The data presented in the figures are from simulations <br /> <br />using the lowest value of upstream depletions. The probability of <br /> <br />reservoir failure increases and the variability in the tails of these <br /> <br />distributions increases as depletions increase. <br /> <br />6.2.4 Comments on the Presence of Variations in the Probability of <br />Reservoir Failure <br /> <br />The simulation results presented in Section 6.2.3 display the <br /> <br />difficulty encountered in attempting to determine the probability of <br /> <br />reservoir failure. Because the values obtained depend upon the stream- <br /> <br />flow sequence used, the true probability of reservoir failure remains <br /> <br />