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<br />constructed with the purpose of impounding . <br />water for flood detention and are owned, <br />operated, and maintained by a government <br />body. Detention structures that are randomly <br />located, pri vately owned, or pri vately <br />maintained shall not be included in the <br />hydrologic analyses unless it can be shown <br />that they exacerbate downstream peak <br />discharges. <br /> <br />6. Previous Studies. Where appropriate, <br />available floodflow-frequency information <br />shall be used so that previous work by <br />Federal, State, or local agencies shall not be <br />duplicated. Where such data are not <br />available, where conditions have changed <br />significantly, or where the methodologies or <br />data used in previous studies are not <br />appropriate, a new hydrologic analysis for <br />each stream shall be prepared. <br /> <br />A comparison of any proposed discharges wi th <br />all published or unpublished floodflow- <br />frequency data that exist for the study area <br />shall be provided to the Board. <br /> <br />Proposed flood discharges shall. be compatible . <br />wi th those used in previously completed <br />studies on the same watercourse. The results <br />of a later floodflow-frequency analysis shall <br />be considered, where they disagree with <br />discharges used in completed studies, only <br />when they can be shown to be significantly <br />different statistically than the previously <br />used discharges. The test for significance <br />shall be based on the confidence limits of the <br />latest analysis, as described below. <br /> <br />Where a later floodflow-frequency analysis <br />provides discharges that differ from those <br />established previously in studies on the same <br />stream, the latest discharges shall be adopted <br />if the previously established discharge do not <br />fall within the 95 and 5 percent confidence <br />limits (90 percent confidence interval) of the <br />most recent estimates. The previously <br />established discharges shall be adopted if <br />they fall within the 75 and 25 percent <br />confidence limits (50 percent confidence <br />interval) of the most recent estimates. Where <br />the previously established discharges fall <br /> <br />. <br /> <br />. <br /> <br />-14- <br />