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Alternative #3. - Alternative }3 consists of elevating all structures in Rosevale above the lOO-year flood elevation. structures would be raised anywhere from 1 foot to about 5 feet above the existing first floor elevations. The constant and variable costs would the same as those described in the Riverside Alternative #3. The alternative does not address potential bank erosion problems. Residual damages with this alternative would include damages to streets and utilities and cleanup of sediment and debris after a flood. . 10. Comparison of Alternatives. Tables 5 and 6 give a comparison of the first and annual costs as well as annual and net economic benefits and the benefit-cost ratio. Residual flood damages were estimated to include emergency debris clearing and levee damage control, some police monitoring and traffic control, and interior drainage pumping. All structures and contents in the flood plain would be protected to the lOO-year level of protection. As shown on the tables, none of the alternatives in either area were economically justified. TABLE 5 RIVERSIDE ALTERNATIVES! ($1,000) . Alternative Item #l #2 #3 First Cost 865 1,500 760 Annual Cost 77 l33 67 Average Annual Benefits 42 42 36 Net Economic Benefits -35 -9l -3l Benefit-cost Ratio 0.5 0.3 0.5 1100-year level of protection, October 1990 price levels. Alternatives #l and #2 most appeal to the sponsor. Both consist of various lengths of levee and floodwall for the Riverside area. However, neither alternative is economically justified. Alternative #3, the nonstructural alternative to elevate each individual structure, would also not be economically justified and is also not supported by the sponsor. 14 .