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<br />C? <br />..::; <br />N <br />t~'" <br />00 <br />W <br /> <br />151 <br /> <br />discharges are released, and the final storage calculated as the <br /> <br />difference between inflows and outflows. The total evaporation <br /> <br />is then compared to USBR estimates. The total changes in storage and <br /> <br />final storage are compared to measured values over the period. Large <br /> <br />discrepancies in evaporation would indicate poor modeling technique. <br /> <br />Large discrepancies in storage or storage change would reflect poor <br /> <br />modeling of evaporation as well as indicate where other processes, <br /> <br />such as bank storage, have been either poorly modeled or neglected. <br /> <br />Two periods were examined during validation. The first period, <br /> <br />1941 to 1962 precedes the completion of Glen Canyon Dam. This period <br /> <br />was chosen so that initial filling and bank storage accumulation of <br /> <br />Lake Powell would not affect water and salt budgets. Lake Mead, which <br /> <br />began filling in 1933, had reached steady state operation by 1941. <br /> <br />The second period examined was 1963 to 1968. <br /> <br />A schematic representation of reservoir operation in the va1ida- <br /> <br />tion model is shown in Figure 5.3. <br /> <br />1941-1962 <br /> <br />The measured or estimated water and salt budgets, and the modeled <br /> <br />budgets for the 1941 to 1962 period are shown in Table 5.1(a,b). <br /> <br />Two areas of agreement in the water balance should be noted: <br /> <br />(1) the net change in storage of Lake Mead is matched by the model, <br /> <br />and (2) the net evaporation from Lake Mead is also matched. These last <br /> <br />two items indicate that the net effect of changes in bank storage or <br /> <br />other possible losses are small and within the accuracy of the measured <br />