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Ci4JJ flows every 2 to 10 years. In terms of the effects of such floods on reservoir storage levels, a most significant parameter is flood volume. USBR hydrologic studies, based in part on 68 years of record of stream flow near the site suggest the following n-e- quency relationship: Flood Frequency Flood Volume af. 200,000 340,000 580,000 1,000,000 2,000,000 Once in 10 yr. Once in 25 yr. Once in 100 yr. Once in 1000 yr. Probable Ma..ximum Flood The possible significance of these quantities lies in the suggestion that, with reasonable operation of the low level outlets through the dam, and appropriate position- ing of the spillway lip, the Joint Use and Normal Flood Control space below Elev. 4428.5 could completely regulate a Once in 100 yr. Flood. Stated another way, it is only re- motely,probable that the reservoir would rise above Elev. 4428.5 more than once in the ne},:t 100 yr. 2. Reservoir Operation. The reservoir is a multi-purpose project. Pri- rnar ily , it would seem that water conservation operations would be the essential feature. Secondarily, but of first importance in relation to loading and seepage effects on the dam and its foundation, flood control storage in the highest anticipated levels of the res- ervoir becomes the matter of greatest interest. From the portions of several hydrologic - reservoir operation studies furnished to us, it would appear that varying degrees of conservatism have been employed in assumptions of reservoir levels preceding storm runoff and in assumptions of reservoir releases during flood inflows. One summary, which appears to have employed reason- able assumptions, showed that the reservoir would never have risen above Elev. 4428.73 with normal regulation of storage during the 68 years (1905 to 1973) of record. This summary included the effect of the great storm of May 1973 which caused a peak flow at the site of about 27.000 cis and a volume of over 500,000 ai. 9.