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ft ;~ not known how many flood insurance policies are in effect in the Dry Creek flood plain. It is also difficult to predict the rate at whieh existing structures would be insured in the future, A total of 471 structures would be removed from the lOO-year flood plain if the JOO-year plan were constnlcted, To the extent these structures are clIrrently insured or will be insured in the future, an economic bendit wOl.lld resl.llt; however, thisbenef1t has not been quantified. BESEFlT-COST RATIO Table 6-4 contains an economic slImmary of both plans. As shown, tile total eco- nomic cost for the lOO-year plan would be $6,171,700. The annl.lal cost would be $519,300. Estimatedannllal benefits would beS444,200, ri:sultinginabencflt-costratio of 0.86. This plan wOllld have netannllal bencfitsof.$75,lOO. ~REASEn RECREATION OPPORTU~ITlF.s The possibility e:dsts for using the potential diversion channel for recreational purposes. Thc most likely use would be for a trail connecting with the POlldre TraiL This potential benefit and its associated cost have not been quantiflcd. As shown on table 6-4, the total economic cost for the 30-year plan would be $3,642,800. The annual cost would be $305,600. Estimated annllal benefits wOllld be $370,200, resulting in a bencfit-cost ratio of 1.2. This plan would have net annual bencfitsof$64,600. LA:'o'J) V ALUf, ~:NIIA~CEMENT Removing lan<J from the flood plain and floodway would increase its value, To the exlcnt this incrcase is rc1atcd to the more efficicntutilization ofr esourees. itcolllJ bccons;deredaprojcctbenefit. This potcnlial bc[\efit has not bee[\ quantified. RISK AND UNCERTAINTY Statistics that can be described by pr\lbability distributions can bc J,--alt with through risk analysis. Uncertainty deals with phenomenon thatcannOl be descrihed by a probability distribution, ECONO\1IC COSTS F.conomic costs consist of the first cost, interelt during construction (!DCl,and operation an<J maintenance (O&M) costs. The first cost inclllJes tile costs reqllirw to eOl\struct the projcct. including costs for design and administra tion,landacquisition,and relocation costs, IDC il delcrmincdusing tilc Federal discount rate and considers the amount of fund, l1'quircd and the length of time for construction, O&M costs are the estimated annual costs of opcrating and maintaining the project. 0&/1.1 C<.lsts arc csti- matcJ tu bc $5.000 p.::r year for tile 30)'e.1r ;11a.1 and $10,000 for the IOO-ycar plan. In thc analysis oflhe estimate of the flO(l(j damages, errors could be prescnt in tile estimatcdvalucs, hydraulics, land useclevat;ons, and hydrology, The uncertainity in the Airpark area may be of significant importance. The feasibility study involves morc detailed analysis and dalll col!oction that attempts to re<:!lIce many ofthcsc uncertainitics. Some degrec of risk and uncertainty is present in any wmerresourc e plan because of data Hmitationsoroth,'rrcaS<lns. There are many factors that inflllence the basic data which, in hml, influence the reliability of the study conclusions, [n thc Fort Collins llrca, there arc three factors which involve a certain degree of uncertainty: (I) there is no strel\m gage data for Dry Creek. (2) the n1l1l1erous irrigation canals that cross Dry 6-17 6.18