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<br />18 <br /> <br />greater) flood than a low frequency (2 t.O 5 year) flood. <br /> <br /> <br />A complicated model basin st:.udy 'would be required to relate <br /> <br /> <br />the effect of diversion and cont:rols on a. parLLcular fre-' <br /> <br /> <br />quency flood. For lack of mor'e :lata, the 2~;% reduct:.Lon of <br /> <br /> <br />floods due to controls was applied to t.he 50 year flood <br /> <br /> <br />frequency. The small difference in final design discharge <br /> <br /> <br />would not warrant a more detailed Sbldy. <br /> <br /> <br />The period of records before 1934 are relatively un- <br /> <br />affected by diversions or controls. <br /> <br />Using this as a base <br /> <br />for unaffected flood peaks, a 25% reduction was made from <br />the Discharge vs. Drainage Area Curve (figure 5) to predict <br />the 50 year flood. This dis,chargc read from 1'.i.gure ') is <br />54,000 cfs. Therefore the :c,O yea.r design flood for De.Beque <br />Canyon would be 25% less t:han 54,C'OO cfs or 41,.000 cfs. <br />A design recurrence inte:rva,l. c:urve, figurE~ 6, WiiS COD'- <br />st:r'ucted using figures 12 t:i.~nl ).."'" The design mean annua.l <br />flow is 22,000 cfs. <br />The flood records llsee. :u; a:."J.ysi,s did not: reflect an! <br />reducti.on that the most: l:ecent D',,': cr\loi1's may have on pee.k <br />discharges. By the same t.O'''~~, ,'le itlJe1' was increased rune fr: <br />due. to weather modif.icatior. incl',)6\;;d" Since bot:.h of these <br /> <br />factors are difficult to prea~ct and could be cffsettlng, <br /> <br /> <br />they were neglected i.n 'l:he fi.nal analysis" <br />