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10 <br /> from that of using the formula. Depletions are an input to the model rather <br /> than an output. It was therefore necessary to specify a depletion level and <br /> then verify other parameters such as shortages and storage used. Even the dep- <br /> letion level could not be specified exactly because the reservoir evaporation <br /> portion of the depletion varies with the operation of the reservoir and is <br /> dependent on water surface areas and evaporation rates. Another major dif- <br /> ference between the model approach and the formula approach is that in the model <br /> - just as in the real world, the streamflow and the demands are both spacially <br /> and temporally distributed, i.e. , there may not be water available to meet <br /> demands at a given point in the basin at a given point in time. The formula <br /> approach, however, assumes that all of the water is available to meet all of the <br /> demands above Lee Ferry. <br /> One model run was made in an effort to confirm the 5.8 MAY computerized formula <br /> run. Bank storage release was restricted to zero and the maximum drawdown on <br /> the reservoirs constrained to minimum power pools. The storage used by the <br /> model was 20.7 MAF (vs. 26.2 in the formula approach) and the average shortage <br /> was 264,000 AF/year or 4.6 percent over the 25-year critical period 1953-1977. <br /> The results of the run indicate an actual depletion obtained of 5.775 MAF. If <br /> an adjustment is made for the difference in storage values used between the two <br /> methods, the remaining storage would be about 1 1/2 percent. An annual release <br /> of 8:27 MAF was made from Lake Powell in this run. <br /> Another model run was made to verify the results of the 6.3 MAF computerized <br /> formula run. The depletion level reached was only 6. 187 MAF, short of 6.3 MAY. <br /> With a Lake Powell annual release of 8.23 MAF and a critical period of 25 years, <br />