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<br />Water-surface elevations of floods of the selected recurrence <br />intervals were computed through use of the U.S. Army Corps of <br />Engineers HEC-2 step-backwater computer program (Reference 7). <br /> <br />-,., <br /> <br />Cross section data for Tenmile Creek were obtained from field <br />surveys and topographic mapping (Reference 8). Cross section data <br />for Meadow Creek were obtained entirely from field surveys. All <br />bridges and culverts were surveyed to obtain elevation data and <br />structural geometry. <br /> <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 was computed (Section 4.2), selected cross <br />section locations are also shown on the Flood Boundary and Floodway <br />Map (Exhibit 2). <br /> <br />Roughness factors (Manning's "n") used in the hydraulic computations <br />were chosen by engineering judgment and based on field observations <br />of the streams and flood plain areas. Roughness values for the <br />main channel of Tenmile Creek ranged from 0.040 to 0.045, while <br />flood plain roughness values ranged from 0.090 to 0.100 for all <br />floods. Roughness values for the main channel of Meadow Creek <br />ranged from 0.030 to 0.035, while flood plain roughness values <br />ranged from 0.075 to 0.085 for all floods. <br /> <br />Starting water-surface elevations for Tennlile and Meadow Creeks <br />were taken at Dillon Reservoir. <br /> <br />K <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 />The hydraulic analyses for this study were based on unobstructed <br />flow. 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 />Shallow flooding areas on Tenmile Creek were determined from the <br />detailed analysis of Tenmile Creek and by field inspection. <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 <br />management measures. <br /> <br />.... <br />\ <br /> <br />6 <br />