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<br />unlimited flood control storage (damage from the uncontrolled local <br />flows). Damages calculated for base conditions (normally natural <br />flows) using selected floods and proportions (ratios) are computed by <br />integrating the base conditions damage-frequency curve or by using <br />a predetermined average annual damage. Expected Annual Damages for <br />modified conditions are computed from the sum of the products of the <br />\ <br />assigne~ exceedence frequency intervals (based on base conditions) and <br />the corresponding damage based on the modified flow. Figure 1, <br />Expected Annual Uamage Computations, graphically portrays the annual <br />damage computations. The damage from the uncontrolled local flows <br />are also calculated in a similar manner to the modified conditions. <br /> <br />The damage reduction due to the proposed system is based on <br />the difference between the expected annual damages for the base condi- <br />tions and the modified conditions. If there is an existing reservoir <br />system the damage reduction can be based on the difference between <br />the base conditions and the modified conditions where the base condi- <br /> <br />tions were determined f~ another simulation run in which existing <br />reservoirs only are simulated. <br /> <br />A separate set of damage data can be used if the modified condi- <br /> <br /> <br />tion damages do not follow the base condition discharge-damage curves <br /> <br /> <br />as would be the case for a levee, channel improvement or nonstructural <br /> <br /> <br />alternative such as flood proofing, relocation, purchase, or flood <br /> <br />plain zoning. <br /> <br />13 <br />