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<br />1\/-5 <br /> <br />100-year return frequency at the designated "design" points, as shown <br />on Sheet 1 , of Volume 2. Figure 1'1'-2 shows the incrementai Increase- <br />peak rate of runoff along the channei. Figure No. IV-3 shows the hy- <br />drographs at specifIc desIgn poInts for the 100'.year flood under future <br />development. <br /> <br />Basin 1 was not used In the hydrological analyses of fiood peaks <br />because the major flow below the U.P.R.R. is controlled by the routIng <br />of water through the rai 1 road culvert, and the incremental increase of <br />flood peak flow due to the 0.7 square mile Basin I is minimal. <br /> <br />Special Considerations <br /> <br />This study assumed that neither Standley Lake nor Great Western <br />Reservoir would pass any significant flood waters durIng the 100-year <br />frequency flood. <br /> <br />The 100-year Inflow hydrographs for each of the reservoirs (BasIns <br />A and B) were routed through assumin<j a full re,servoir, using an In- <br />variable discharge-storage relationship. (Puh Method). It was found <br />that the 100-year flood routed throu<jh Stand 1 ey Lake drops from above <br />9,200 cfs to 1 ess than 400 cfs. The 100-year flood routed through <br />Great Western also Indicated a peak discharge of Jess than 100 cfs. <br />The chances of Standley Lake being spi Ilway-fllll whlen the 100-year rain- <br />fal I comes are much smaller than one in one hundred, so that It was as- <br />sumed that Standley Lake could store the entire 100"year storm when it <br />fa 11 s. <br /> <br />For the 100-year desIgn hydrolo<jy for the channel s downstream of <br />the Standley Lake Reservoir, it was assumed that Standley Lake was <br />makIng a release equal to the mean release dur Ing the summer, which is <br />250 cfs. <br />