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<br /> <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 />- 5 - <br /> <br />Hydroloqic and Hydraulic Analyses <br /> <br />The application of benefit-cost analysis to urban flood <br /> <br />control projects requires the development of hydrology for <br /> <br />the project sufficient to define flood flows and potential <br /> <br />flood hazard areas under existing and various future develop- <br /> <br />ment conditions. Because the extent of flooded land, the <br /> <br />magnitude of potential damage and the cost of preventive and <br /> <br />corrective measures all depend on the magnitude of flood flows <br /> <br />derived from the hydrologic studies, it cannot be over-empha- <br /> <br />sized that the hydrology is of primary importance to the <br /> <br />achievement of a realistic and usable benefit-cost analysis. <br /> <br />Therefore, the most advanced and sophisticated techniques con- <br /> <br />sistent with the scope of the project and the basic data avail- <br /> <br />able should be utilized in the hydrologic analysis. <br /> <br />The benefit-cost analysis requires the computation of the <br /> <br />future flood hydrology for a range of recurrence intervals (at <br /> <br />least three) including the lOO-year. The recurrence intervals <br /> <br />should be chosen to give a representative spread in the peak <br /> <br />flows, i.e. low, medium and high. This will be used to define <br /> <br />the base line conditions from which the effectiveness of each <br /> <br />flood control alternative will be measured. Derivation of run- <br /> <br />off hydrographs is mandatory. <br /> <br />~ Leonard Rice Consulting Water Engineers Inc <br />