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<br />At channel capacity discharge, replacing the Main Street bridge with a <br /> <br /> <br />clear span of the same length would lower the water surface elevation <br /> <br /> <br />just upstream from the bridge by .65 feet. This analysis has assumed <br /> <br /> <br />that no debris is lodged in the bridge opening. Platte Center <br /> <br /> <br />residents have stated that debris does collect in the present bridge <br /> <br /> <br />opening which has 2 piers. Since chis is a problem, replacing the <br /> <br /> <br />present bridge with a clear span bridge would show a greater reduction <br /> <br /> <br />in water surface elevations since less debris would collect in the <br /> <br /> <br />clear span bridge. <br /> <br />The estimated cost of improving only the channel downstream from <br /> <br /> <br />Main Street is $296,950. The cost is based on enlarging the channel <br /> <br /> <br />immediately downstream from Main Street and extending the improvements <br />" <br />approximately 2,000 feet downstI:'eam (figure 5). The total annual <br />costs for this alternative are $~5,990, and the total annual benefits <br />incurred are $2l,800. This alternative has a benefit-cost racio of <br />0.84. <br /> <br />. <br />.' <br /> <br />. <br /> <br />- <br /> <br />... <br /> <br />19 <br />