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. . . , ECONOMIC EVALUATION Benefit-Cost Analysis Table 1 displays investment costs, annual equivalent costs, annual benefits, and benefit-cost ratios for two alternative developments. Flood control was deleted from one analysis because the separable costs associated with that purpose exceed benefits by about $600,000 annually. The last official estimate provided by the Corps of Engineers, dated November 1977, showed annual flood control benefits of $836,000. Table 1 is based on the authorized 3.25 percent discount rate and a 100-year period of analysis. Development of the Narrows Unit including M&I water is economically justified since the benefit-cost ratios are greater th an 1: l. Direct irrigat ion benefits were based on the increased net farm income that could be realized by construction of the unit. Indirect and pUblic irrigation benefits measure resp'ectively the value of processing the increased agricultural production and the expected stabilization of the local economy. An additional benefit would be some OM&R savings to the Jackson Lake irrigators. New water estimated to be available for determinat ion of irrigat ion benefits cons ists of 77,000 acre-feet of stored water to be released annually at the reservoir and 24,500 acre- feet annually of usable return flows, for a total of 101,500 acre-feet. Annua 1 benefits derived from fi sh and wil dl ife enhancement were prov ided in the Fish and Wildlife Service's memorandum of November 4, 1975. The National Park Service computed annual benefits from expected recreat ion visitation at the Narrows Unit and reported those benefits in a memoran- dum dated February 17, 1976. Table 1 reflects a 25,000 acre-foot yield available annually for beneficial use by M&I entities. Benef;its are based on $200 per acre- foot, which approximates the current will ingness to pay for existing highly reliable water supplies in the So~th Platte River valley. 6