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9 :� <br />parapet wall may be required on Dams 2 and 3 with the use of concrete facing, or for slopes <br />steeper than 3:1. <br />3.1.2 Spillway Adequacy and Flood Freeboard Requirements <br />For purposes of determining the adequacy of the existing spillway and to evaluate spillway <br />requirements, it is assumed that the inflow design flood for the reservoir would be produced <br />by 75% Probable Maximum Precipitation (PMP) flood with rehabilitation of the existing dams <br />but without increasing the storage capacity, and would be the .100% PMP flood with dam <br />replacement and enlargement alternatives. <br />The inflow design flood was developed and reservoir routings performed using current day <br />criteria. Additional assumptions included starting the flood routings -at the spillway crest <br />elevation, which was set 2.5 feet above the normal water level, and providing 5.5 feet of <br />surcharge freeboard for flood routing. The peak inflow rate into the reservoir, including rainfall <br />on the lake surface, is estimated to be 73,500 `cfs and 54,800 cfs for the 100% and 75% <br />PMP floods, respectively. <br />Due to the relatively small tributary drainage basin size of 6.7 square miles and the relatively <br />large surcharge storage capacity of,the reservoir, the spillway requirements were determined <br />to be modest. The hydrologic' calculations indicate that with the existing spillway, the <br />reservoir can safely route the 75% PMP flood with 2.3 feet of residual freeboard. Routing the <br />100% PMP flood to within 10 foot of the dam crest, the required spillway width would be <br />approximately 240 feet for the current conditions and would be as small as 100 feet wide <br />under the maximum reservoir enlargement alternatives. <br />3.1.3 Inlet Canal' <br />The existing inlet canal currently submerges about 2.0 feet at the elevation of the normal <br />water pool for a distance of about one -half mile upstream from the reservoir. With an average <br />bottom slope of about 2.5 feet per mile, any significant increase in the normal water level <br />would extend the static water pool in the inlet canal upstream for miles. Any enlargement <br />2 %reports197- 1- 500.nk <br />