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, City of Fort Collins December 4, 1980 Page 2 The alternative plans which were submitted to the City at our meeting on October 30, 1980, were all considered feasible for further investigation at that time. Usinq 100 vear de~igv flows \eo,~ basecLon fqllY~ Qev~lQPed basin c_onditionsj1it.h.existinJULmn- t' "'tI9.!l..andchannel_C.9n91~ions, strj)~improvements WeT" <i<.eP ,"}.oj I _and co.n.!itLl,K.t.i.Qrt ilnd-Ql2.eration aod maintenance costs were p<;ti- ,\'~ J:, ' mated, fr:~m_the Unit Cos.t Data Table attached.. S ~nc:p flood damage c.'1.~\V\ ~""~ ~':.alculatlnn< WPr aches, flood control lans wer c D.-,'" -:., ,," j.ide.t;e.d..b,y. rea,d1es. Flood damages Whl C could be expected to ' p," occur after an improvement was constructed were also estimated and the difference between flood damage figures for a given reach before and after a specific improvement is made are the "benefits" which accrue to the reach where the improvement is made. A detailed estimate of construction costs and flood damage eiti- mates for each of these alternative plans is listed by reach in Table 1-4 attached. Construction costs are broken down into five basic components (Columns 1 through 5): channel improvements, street improvements, utility relocations, an engineering and contingency factor, and right-of-way acquisition costs. The summation of these costs (Column 6) is the total capital improve- ment cost of the alternative. This has been amortized over a5Q , . year project life at the'~(L8%",interest rate to produce the annual construction cost (Column 7). To this figure is added the esti- mated annual operation and maintenance cost (Column 8) to deter- mine the total annual improvement cost (Column 9). For each reach, the first alternative listed is the baseline .fSl.rulition. T~ averaqe annual flood damage for the ex is ti ng condition and the residual annual flood damaqe for the other alternaTives appear_.irJ. ~Q lllll)n 1Q,. The annua 1 benefi t (Column 11) is the difference between the flood damage for the baseline condi- tion and the residual flood damage for the particular alternative (Row 1, Column 10 - Row i Column 10). The net annua 1 benefit (Column 12) is the annual benefit less the annual improvement costs (Column 11 - Column g). This figure is the actual dollars in savings (or losses) which would result after implementing the alternative. The total annual cost (Column 13) is the sum of the annual improvement cost and the residual annual flood dam- ages (Column g + Column 10). The benefit/cost ratio (Column 14) is the annual benefit divided by the annual improvement cost (Column 11 + Column 9) of each alternative. It can also be viewed as the dollar return in miti. gated flood damages for each improvement dollar spent. The I . Xes C;",. u.Jc. H ~ ...,e' 7 * % \-::.'/...... ~ -- ! "')-1',:,/ , , 1:.J!.../ 1$ r.o <)., :::'f\"'" C'I . e__