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least six (6) feet and to widen the existing spillway crest from 14 feet to <br />45 feet. Considering the larger reservoir surcharge storage capacity and • <br />larger spillway sizing, both the maximum thunderstorm and maximum general <br />storm can be accommodated while still leaving a minimum of two (2) feet of <br />freeboard. As detailed in the flood routing computations, Tables 12 and <br />13, the maximum thunderstorm provides the short duration peak inflow and <br />worst condition. <br />The recommended spillway would consist of a trapezoidal earthen channel <br />with bottom width equal to 45 feet. Side slopes should be uniform 2 to 1, <br />with the longitudinal slope equal to 1X. The entire channel surface should <br />be covered with Type B,rip-rap to minimize erosion. <br />It should be noted that flood routing computations have assumed that <br />maximum snowmelt and maximum ditchflow would continue for the entire <br />outflow design period. Although highly unlikely in actuality, this <br />theoretically extreme condition would result in a stabilized maximum pool <br />elevation of approximately 55.0 feet. Upon curtailment of ditchflow <br />feeding and dissipation of snowmelt runoff, the reservoir pool elevation <br />would return to 45.9 feet approximately two to three days following the <br />PMTS and/or PMGS. <br />Routing of a succeeding "Assumption A" flood beginning seven days after <br />peak outflow, as recommended in "The Design of Small Dams" for areas <br />receiving less than twenty inches of annual rainfall, has no appreciable <br />effect upon spillway sizing. <br />1• <br />VI-14 <br />