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<br />... <br /> <br />. <br /> <br />. <br /> <br />~ <br /> <br />compared to 25 years of annual streamflow as well as the difference in the <br />amount of storage used in the monthly study as opposed to that which would <br />be used in just 25 years. Both of these adjustments were then applied to <br />the storage value used in the mass balance program. The adjustments were <br />as follows: <br /> <br />Storage Adjustment <br />a) 25 year 7 month <br />b) Adjusted amount <br /> <br />storage <br /> <br />for 25 years <br /> <br />= 24.762 MAF <br />- 24.762 x 25/25.5833 - 24.197 MAF <br /> <br />Streamflow Adjustment <br />a) 25 year critical period average streamflow - 12.97 MAF <br />b) 25 year 7 month critical period average streamflow - 12.81 MAF <br />difference - 0.16 <br />for 25 years: 0.16 x 25 = 4.00 <br /> <br />Total Adjustment <br />24.197 - 4.00 = 20.197 MAF of "adjusted" storage. <br /> <br />The adjusted storage includes the effects of sedimentation and bank <br />storage. Use of this value along with the annual natural flow record at <br />Lees Ferry and a minimum release to the lower basin from Lake Powell of <br />8.23 MAF produced a firm yield for the Upper Basin of 5.55 MAF. The yield <br />varied from 5.55 MAF with no shortages to the Upper Basin to 6.03 MAF with <br />an eight percent overall shortage as shown in Table 1. <br /> <br />The liklihood and magnitude of other shortages or "calls on the river" are <br />discussed in Section 5. <br /> <br />4. Probability Analysis <br /> <br />In addition to calculating the firm yield of the Upper Basin, the mass <br />balance model also calculated the probabilities of various higher yields <br />for given levels of shortages. These probabilities are simple plotting <br />positions or percent frequency and were determined by dividing the number <br />of times an interval of critical period length produced at least the <br />specified yield, divided by the total number of times an interval of <br />critical period length could occur in the total record (from 1906 to 1986). <br />The results are tabulated in Table 1 which also indicates the length of the <br /> <br />7 <br />