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<br />Location. of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profile. (Exhibit I), and are also shown on <br />the Flood Insurance Rate Map (Exhibit 2). <br /> <br />Floodplain roughness factors <br />computations were selected based <br />floodplain conditions (Reference <br />this study are listed below: <br /> <br />(Manning IS "n") used in these <br />on field inspection of the actual <br />1). The roughness factors used in <br /> <br />Channel area <br />Overbank area (fields) <br />Developed overbank areas <br />(within city): <br /> <br />n 0.03S <br />n = 0.030 <br /> <br />n = O.OSO <br /> <br />Starting water-surface elevations for Beaver Creek were based on a <br />statistical analysis of recorded stream flow records for comparable <br />drainage areas in the high plains area of eastern Colorado, western <br />Kansas, and southwestern Nebraska. <br /> <br />Flood profiles were drawn showing the computed water-surface <br />elevations for floods of the selected recurrence intervals. <br /> <br />The hydraulic analyses for this study are based on unobstructed <br />flow. The flood elevations shown on the profiles are thus <br />considered valid only if hydraulic structures remain unobstructed, <br />operate properly, and do not fail. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum (NGVD) of 1929. Elevation reference marks used in this study <br />are shown on the maps; the descriptions of the marks are presented <br />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 <br />management programs. Therefore, each Flood Insurance Study <br />floodplain boundary map designed to assist communities in <br />sound floodplain management measures. <br /> <br />floodplain <br />includes a <br />developing <br /> <br />4.l Floodplain Boundaries <br /> <br />To provide a national standard without regional discrimination, the <br />I-percent annual chance (lOO-year) flood has been adopted by FEMA <br />as the base flood for floodplain management purposes. The 0.2- <br />percent annual chance (SOO-year) flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied by detailed methods the boundaries of the 100-and SOO-year <br />floodplain boundaries have been delineated using the flood <br />elevations determined at each cross section. <br /> <br />11 <br />