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<br />- r 11 <br />L'" 1- , <br />'v - <br /> <br />flows every 2 to 10 years. In teTms of the effects of such floods au reservoir storn.ge <br />levels, a most slgnificac.t parameter 15 flood volume. USBR hydrologIc studies, based <br />\n part On 68 year3 of record of stream {lOVI near the site suggest the fanowing fre- <br />quency relationshIp: <br />Flood Frequency Flood Volume <br />ai, <br /> <br />:17 <br /> <br />Once In 10 yr, 200,000 <br />Once In 25 yr. 340, 000 <br />Once In 100 yr. 580,000 <br />Once in 1000 yr, 1,000,000 <br />Probable :Ma."(lmum Flood 2,000,000 <br />The IX>sslble signifIcance of these quantities lies in the suggestion that, with <br />reasonable operation of the low level outlets through the dam, and appropriate position- <br />ing of the spillway Bp, the Joint Use and Normal Flood Control space below Elev. 4428.5 <br />could completely regulate a Once 1n 100 yr. Flood. Stated another way, it is only re- <br />motely probable th3.t the reser'voir would rise above Elev. 4423.5 more than once In the <br />nexll00 yr, <br />2. Reservoir Operation. The reservoir is a multi-purpose project. Pri- <br />marily, it would seem that water conservation operations would be the essential feature. <br />Secondarily, but of first Import:mce in relation to loading and seepage effects on the <br />dam and its fOlDldation, flood control storage in the highest anticipated levels of the res- <br />ervoir becomes the matter of greatest interest. <br />From the portions of several hydrologic - reservoir operation studies furnished <br />to us, it would appear th3t varying degrees of conservatism have been employed in <br />assumptions of reservoir levels preceding storm runoff and in assumptions of reservoir <br />releases during flood inflows. One summary, which appears to have employed reason- <br />able assumptions, showed that the reservoir would never have risen above Elev. 4428.73 <br />with normal regulation of storage during the 68 years (1905 to 1973) of record. This <br />summary included the effect of the great storm of May 1973 which caused a peak flow at <br />the sUe of clJout 27 I 000 cfs and a volume of over 500,000 af. <br /> <br />9, <br />