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<br />4. Freeboard allowances <br /> <br />a. Introduction. - Freeboard provides a margin of safety against <br /> <br /> <br />overtopping failure of dams. It is not necessary to prevent occasional <br /> <br /> <br />overtopping of a dam by waves under extrene conditions. The number and <br /> <br /> <br />duration of such occurrences, however, should not threaten the struc- <br /> <br /> <br />tural integrity of the dam, interfere with project operation, or create <br /> <br /> <br />hazards to personnel. Freeboard provided for concrete dams can be less <br /> <br /> <br />conservative than for enbankment dams because of their resistance to <br /> <br /> <br />damage or erosion. Special consideration may be required in cases <br /> <br /> <br />where a powerplant is located near the toe of the dam. <br /> <br />Normal freeboard is defined as the difference in elevation between the <br /> <br /> <br />top of the dam and the higher of either the top of conservation storage <br /> <br /> <br />or top of joint-use storage as established by design requirenents. <br /> <br />Minimum freeboard is defined as the difference in elevation between the <br /> <br /> <br />top of the dam and the maximum reservoir water surface that would <br /> <br /> <br />result from routing the IDF through ,the reservoir. Intermediate <br /> <br /> <br />freeboard is defined as the difference between an intermediate storage <br /> <br /> <br />level and the top of the dam. Intermediate freeboard may be applicable <br /> <br /> <br />when there is exclusive flood control storage. <br /> <br />b. General quidelines. - Following are guidelines for determining <br />appropriate freeboard allowances. <br /> <br />. Freeboard allowances should be based on site-specific conditions <br />and type of dam (concrete or embanklllent). <br /> <br />24 <br />