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<br />An analysis of the hydraulic characteristics of Oak Creek waS <br />performed in order to determine water-surface elevations for the <br />laO-year flood. Bridge elevations and sizes of openings were <br />surveyed and measured in the field on January 21 and 22, 1986. <br />These data were combined with cross section data on Oak Creek <br />taken from a 2-foot contour mapping of the Town of Oak Creek <br />(Reference 5). These cross section data became the input data in <br />the U. S. Army Corps of Engineer HEC-2 step-backwater computer <br />program. <br /> <br />Locations of selected cross sections used 1n the hydraulic <br />analysis are shown on the Flood Profiles (Exhibit 1) and Flood <br />Insurance Rate Map (FIRM) (Exhibit 2). <br /> <br />Roughness coefficients (Manning t 9 "n" values) were also used as <br />HEC-2 input. Roughness values for Oak Creek varied from 0.035 <br />far the channel to 0.040 for the overbank areas. <br /> <br />Critical depth was the starting water-surface elevation at a <br />location several hundred feet downstream from the study reach. <br /> <br />Flood profiles were drawn showing the computed water-surface <br />elevations for floods of the selected recurrence intervals. <br /> <br />The hydraulic analysis for this Flood Insurance Study is based an <br />unobstructed flow. The flood elevations shawn on the profiLes <br />are thus considered valid only if hydraulic structures remain <br />unobstructed, operate properly, and do not fail. <br /> <br />All eLevations are referenced to the National Geodetic Vertical <br />Datum of 1929. Elevation reference marks used 1n this Flood <br />Insurance Study are shown on the maps; the descriptions of the <br />marks are presented in Elevation Reference Marks (Exhibit 3). <br /> <br />4.0 FLOODPLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages state and local governments to adopt sound flood- <br />pLain management programs. Therefore, each Flood Insurance Study <br />includes a floodplain boundary map designed to assist communities in <br />developing sound floodplain management measures. <br /> <br />4.1 Floodplain Boundaries <br /> <br />To provide a national standard without regional discrimination, <br />the 1 percent annual chance (lOO-year) flood has been adopted by <br />FEMA as the base flood for floodplain management purposes. ['or <br />the stream studied by detai led methods, the LOO-year floodplain <br />boundaries have been delineated using the flood elevations <br />determined at each cross section. <br /> <br />Between cross sections, the boundaries were <br />U. S. Geological Survey topographic maps at a <br />with a contour interval of 20 feet (Reference <br /> <br />interpolated using <br />scale of 1:24,000, <br />6) . <br /> <br />6 <br />