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,"5 Eight master plan alternatives were developed for Lena Gulch. Explana- tions of these eight alternatives are presented in Section VI. From these eight alternatives, three were identified for detailed analysis as the result of a meeting with the local entities, on December 5, 1973. Table 1-3 presents a tabulation of the approximate cost estimates of the eight schemes. TABLE 1-3 APPROXIMATE COST ESTIMATE OF ALTERNATIVES PHASE ,~ (Mi II ions of Do; lar's) Alternative Deep Tunnel Surface Conduit Lined Channel Unimproved Floodplain Grass-Lined Channel Estimated Flood Plain Detention Ponds Cost 10.7 9.2 8.5 8.2 6.4 4.3 4.2 The alternatives designated for further detailed research were the grass- I ined channel, the estimated optimum combination and the improved flood- plain. Wright-McLaughl in recomrrlended the Estimated Optimum Combination Alternate based on further analysis. The estimated optimum combination is, as the name denotes, a combination using ;lnon-structuraPI flood pla.n zoning in undeveloped suitable areas, grass-j ined channel in some develop- ed areas, and a few minor reaches of structural channels where developm(~nt is dense and expensive to remove. The tool used to determine the relative merit of the three chosen schemes, was "benefit cost analysis.11 The important consideration in such an analysis is that all estimates must be mutually consistent. In each evaluation, the same basis for estimating prices, calculation methods, and economic factors was used. This continuity in calculation methods gave a realistic comparison between alternatives. The anticipated annual costs include the damage dollars to be paid. Table 1-4, which 'is the same as Table VII-9 is a summary of the alternatives along the entire reach of Lena Gulch. PHASE B SYNOPSIS The purpose of Phase B of this study was to develop a master plan for Lena Gulch based on the chosen alternative.