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<br />Locations of selected cross sections used in the hydraulic analyses <br />are shown on the Flood Profiles (Exhibit 1). For stream segments <br />for which a floodway is computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibi t 2). <br /> <br />Roughness coefficients (Manning's "n") used in the hydraulic com- <br />putations were chosen by engineering judgment and based on field <br />observations of the streams and flood plain areas. For the Eagle <br />River, a roughness value of 0.040 was selected for the channel; <br />the overbank "n" values ranged from 0.040 to 0.100. For Turkey Creek, <br />the channel "n" value was 0.045; the overbank values ranged from 0.040 <br />to 0.100. <br /> <br />Starting water-surface elevations for the Eagle River were calculated <br />using critical depth downstream of the corporate limits on the Eagle <br />River. Starting water-surface elevations for Turkey Creek were <br />derived from the calculated flood elevations on the Eagle River. <br /> <br />Flood profiles were drawn showing computed water-surface elevations <br />to an accuracy of 0.5 foot for floods of the selected recurrence <br />intervals (Exhibit 1). <br /> <br />Depths of shallow flooding areas along Turkey Creek were determined <br />using normal depth calculations. <br /> <br />The hydraulic analyses for this study were based on unobstructed flow. <br />The flood elevations shown on the profiles are, thus, considered <br />valid only if hydraulic structures remain unobstructed, operate <br />properly, and do not fail. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in the study <br />are shown on the maps. <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />A prime purpose of the National Flood Insurance Program is to encourage <br />state and local governments to adopt sound flood plain management pro- <br />grams. Each Flood Insurance Study, therefore, includes a flood boundary <br />map designed to assist communities in developing sound flood plain manage- <br />ment measures. <br /> <br />4.1 Flood Boundaries <br /> <br />In order to provide a national standard without regional discrimina- <br />tion, the 100-year flood has been adopted by the Federal Insurance <br />Administration as the base flood for ~urposes of flood plain manage- <br />ment measures. The SOO-year flood is employed to indicate additional <br />areas of flood risk in the community. For each stream studied in <br /> <br />7 <br />