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<br />Water-surface elevations of the ,10- and 100-year floods were computed <br />using the U.S. Army Corps of Engineers HEC-2 step-backwater computer <br />program (Reference 9). The starting water-surface elevation was <br />derived from hand computations for the peak flow at Pecos Street. <br />The computation derived rating curves for pressure and weir flow <br />at Pecos Street crossing. The culverts at Holiday Glen and Holiday <br />Circle were included in the HEC-2 models. However, three long <br />culverts that have limited capacity to fully contain the 10- and <br />100-year peak flows were not included. These culverts extend from <br />the east branch of Holiday Circle to 100 feet downstream of Holiday <br />Vale; from the east branch of HQliday Terrace downstream 200 feet; <br />and from Holiday Parkway downstream 200 feet. The culvert under <br />Holiday Parkway is submerged due to backwater from Pecos Street <br />for the 10- and 100-year floods, <br /> <br />An approximate flood plain analysis was carried out for Niver Creek <br />and Tributary L of Niver Creek using assumed depths based on a <br />review of the Tributary M profile and available hydrologic <br />information, extensive field reQonnaissance, and engineering judgment. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in this study <br />are shown on the maps. <br /> <br />4.0 FLOOD PLAIN J1,M~f\G~N!..gP~~.~TIONS <br /> <br />The NFIP encourages State and local governments to adopt sound flood <br />plain management programs. Therefore, each Flood Insurance Study prOduces <br />maps designed to assist communities in developing flood plain management <br />measures. <br /> <br />4.1 Flood Boundaries <br /> <br />To provide a national standard without regional discrimination, <br />the 1 percent annual chance (lOp-year) flood has been adopted by <br />FEMA as the base flood for flood plain management purposes. For <br />each stream studied in detail, ~he 100-year flood plain boundaries <br />have been delineated using the tlood elevations determined at each <br />cross section. Between cross s~ctions, the boundaries were inter- <br />polated using topographic maps at a scale of 1:1,200, with a contour <br />interval of 2 feet (Reference B). <br /> <br />As a result of the scope of work for this study, no SOO-year flood <br />boundaries were delineated. <br /> <br />Small areas within the flood plain boundaries may lie above the <br />flood elevations, but cannot be: shown due to limitations of the <br />map scale and/or lack of detail~d toj?ographic data,. <br /> <br />8 <br />