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48 type III and Pearson type III frequency analyses were performed, and the Pearson type III was found to be more applicable. This decision was based on both theoretical considerations and results of analyses of the data. The' frequency analysis was performed for volumes with durations of one month, two months, etc. An adjustment was made to the results to arrive at 100-year peak 30-day volumes, 60-day volumes, etc. based on the 100-year peak one monthly volume, two monthly volumes, etc. This adjustment, used to compensate for the fixed interval of the base data, was very small. It was less than 6 percent for 30 days and practically negligible for periods longer than 60 days. An inspection of the data shows that the adjustment was not dependent on the magnitude of runoff. These flood frequency curves are illustrated on figures 4.1 and 4.2 for Lakes Powell and Mead, respectively. The resulting 100-year volumes were used with the balanced hydrograph procedure to arrive at daily hydrograph values. The values near the peak, those for the peak thirty days, were patterned to resemble the shape of the peak experienced during the natural runoff into Glen Canyon Dam in 1984. The remainder of the hydrograph was patterned to reflect a shape typical of that normally experienced in high runoff years. The timing within the year was also determined based on that normally experienced in high runoff years. The 100-year peak volumes were examined for temporal consistency. The values for the 90-day peak volume appeared excessively large with respect to all of the other values. Therefore, in order to arrive at a reasonably consistent hydrograph, the 90-day values were adjusted downward. This adjustment amounts to 2 percent for the inflow into Hoover Dam. The intervening flows are approximately 5 percent or less of the total and were also smoothed temporally for consistency. It should be noted that as a computational expediency the peak 10, 11, and 12 month volumes were calculated using water year data, but these values were used in constructing a hydrograph for the calendar year. This discrepancy is insignificant in terms of this study. 4.3 ANTECEDENT FLOODS FOR HOOVER AND GLEN CANYON The resulting ordinates of the 100-year hydrograph for inflow into Hoover Dam are shown in table 4.1. Table 4.2 provides the ordinates for the 100-year inflow hydrograph for Glen Canyon Dam, and table 4.3 lists the concurrent flow in the intervening reach between Hoover and Glen Canyon Dams. The ordinates from tables 4.2 and 4.3 for any given day sum to give the corresponding unregulated, undepleted daily flow in table 4.1. Table 4.4 summarizes the results of the separation technique used in the snowmelt flood analysis. The method calculated a 100-year balanced snowmelt hydrograph for flows into Glen Canyon, with the remainder of the 100-year inflow to Hoover Dam coming from the intervening area between the dams.