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<br />SECflON VII <br /> <br />BENEFIT COST ANALYSIS <br /> <br />EXPLANATION <br /> <br />The three alternatives-Improved flood plarn, grass-lln~,d cl1annel, ,,,nd <br />estimated optimum combInatIon-were deslgnllted by the local entitIes <br />and engIneering estImates to be the better choIces. ThIs was true <br />especially In"conslderatlon of the ope,ratlon and malntemance costs <br />of the other alternatives, whIch were clearly much hIgher. The deter- <br />mination of the optImal alternative, hOloJever, Is much more complicated. <br />The principal reasons for this compllcatlCl11 Include the, determlnati'on <br />of: <br /> <br />1. The most suitable alternatIve for each entity. <br /> <br />2. The best design frequency ln light of the damages resultln9 from <br />the frequency chosen. <br /> <br />3. metall design facts and cost estimates. <br /> <br />4. Intangible benefits. <br /> <br />Because each of the th ree a !ternat I ves cho!,en are to be eve I uated for <br />three desIgn frequencies (10,25, and 100 year), there are nIne dIstInct <br />design variatIons to be considered for each Elntlty. Since there are <br />four entities, 36 task Items had to be InvElstlgated b,ef,ore a veil Id re- <br />cOll1T1endatlon could be made. <br /> <br />The present tool used to determIne the rel,a,tlve merit of the schemes, <br />i9S requIred by the engineering agreement wIth the Urbi9n Dndnage and <br />Flood Control DIstrict Is "Benefit Cost AnalysIs." The important con- <br />sideration ln such an analysIs Is that all estimates must be mutually <br />consistent. In each evaluatIon, t~e same basis for estimating prices, <br />,:alculatlon methods, and economIc factors ,,,as used. ThIs contInuity In <br />calculatIon methods gave a reallstlc comparison between alternatIves. <br />The comparison Is In the f~rm of benei'l't t,) cost ratl()s realized and <br />the probable annual costs. The ant1clpatad annual cosU Include <br />average annual damage in dollars. This analysis will indicate the best_ <br />~:omparative alternative and its appro~i'matl:...s~-ang,:.. It s~ould be <br />,-ealized that future development and Increased runoff from this develop- <br />ment wi 11 not occur for many years. Yet, the present worth computations <br />assume that such future development in the basin (and related flood siz- <br />ing) already exist. <br />