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I I I I I I I I I I I I I I I I I I I 7.0 ALTERNATIVES 7.1 GENERAL The overall objectives of the alternatives are to minimize construction cost, reduce the risk of overtopping of the dam between Phase I and Phase 2 construction, and begin construction during 1996. 7.2 EXISTING CONDITIONS The VRA expended $25,350 on the investigation of relining the low-level outlet before the magnitude of the problems with the low-level outlet were realized. An additional $97,509 was expended to construct the dam breach. Engineering services for the feasibility report, low-level outlet investigation, plans and specifications, alternatives analysis, breach design plans and specifications, limited construction observation, embankment and fill material collection, and laboratory testing are approximately $66,432. Surveying cost for developing a 2-foot contour map was $2,200. Thus, total expenditures for engineering and construction to date are approximately $191,491. Alternative] - Drop Inlet Spillway Alternative I includes replacing the low-level outlet with a hydraulically operated gate inlet structure and a 36-inch-diameter welded steel pipe. The drop inlet spillway portion would consist of an 8-foot inside diameter overflow crest (El. 8594) located at a transition from the low-level 36-inch pipe to a 6-foot-diameter welded steel outlet pipe, and a concrete exit structure. The drop inlet principal spillway structure will pass the 100-year design flow without overtopping the dam (Qoutflow = 920 cfs). At this time, as a result of the CDWR moratorium on current PMP estimates discussed previously, the proposed emergency spillway section under this altemative would consist of a 45-foot-wide, 4-feet-high fuse plug to pass the 100-year flood through the service spillway. When the fuse plug fails for storms greater than the 100-year event, the emergency spillway has an additional 4560 cfs without overtopping the dam. In 242161RI.DOC 02-12-97(3,08PM)/RPT 7-1