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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />alternatives also provide a secondary benefit of open space preservation. As with environmental <br />disturbance, attaching a dollar value to this intangible is difficult and it has not been included in <br />the benefit/cost analysis. <br /> <br />B/C Ratios. Costs, benefits and computed benefit/cost ratios are presented in Table II-7. From <br />the table it is evident that the Partial Detention Alternative provides the highest benefit/cost ratio <br />of the three alternatives. Note that full detention of flood flows does not provide greatly <br />increased benefits over partial detention because the majority of costs associated with flooding <br />are attributable to sediment deposition. Although the Partial Detention Alternative detains only a <br />portion of the storm hydrograph, it has been assumed to remove 75 percent of the sediment load. <br /> <br />Based upon the analysis of benefits and costs, the Partial Detention Alternative has been selected <br />as the preferred alternative. <br /> <br />ll-6 <br />