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INTRODUCTION PLAN FORMULATION AND~:VALUATION Fifty alternative plans of project modification WE!re initially considered for the reconnaissance study. Cost estimates have been developed for l~3 of these al ternativE!S. The alternatives inCludE! thE! followin/\ plans either on an individual basis or in combination with each other: Alternative 1 Alternative 2 Alternative 3 Alternative 4 AlternativE! 5 AlternativE! 6 Alternative 7 Alternative 8 Widen the existing spillway. Add a chute spillway on embankm,.nt, Add a side channel spillway near left: abutment. Add a channel spillwa,y at: left abutment. Construct an additional upstream rese:rvoir at the Castlewood site. Harden the dam faCE!, Raise the daJll cr"st by 3 to 19 feet. No action. Initially, the majority of the new spillway alternatives WerE! evaluated b.'3.sed on a single constant invert elevation of 5600 feet m. s .1. so that direct comparisons could be made between the alternative costs without introducing another variable, Later, after initial analysis was perfOlCmed and likely candidates were selected, a higher Gpillway invert of 5613 feet m.s,l. (25 pE!rcent of PMF) was evaluated to determine cost "ffectiven.ss, Elevations lower than 5600 feet m. s.1. have not been examined for this study. Elevation 5600 feet m.s.I. is 4 feet above the standard project flood maximum pool. However, it is about 8,5 feet below the existing invert of th. spillway which has been silted in by slough materials from thE! side Glopes of the spilhmy. Four separate embankment crest elevations have been considered for the dam raise alternatives. These elevations were 5648,5654,5660, and 5664 feet m,s,l, which are 3, 9, 15, and 19 feet above the design crE!st elevation of 5645 feet 39