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<br />Creek Tributary No.7. All bridges and other significant hydraulic <br />structures were field checked for elevation data and structural <br />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 is 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 (Manning1s "n" values) were for the most part <br />adopted from the U.S. Army Corps of Engineers report (Reference 7) <br />after field observations and verification. For Bear Creek Tributary <br />No.7, channel roughness factors were determined based on engineering <br />judgment during field checks. Roughness factors for the main <br />channel of Bear and Mount Vernon Creeks ranged between 0.04 and <br />0.06; the overbank area factors ranged from 0.10 to 0.20. Flow <br />in Bear Creek Tributary No. 7 is normally very low, allowing dense <br />vegetation to obstruct the channel. The roughness factors here <br />ranged from 0.05 to 0.15 for both the main channel and the overbank <br />areas. <br /> <br />Profiles of the streams were started at critical depth; the Bear <br />Creek profile was started downstream from the Morrison corporate <br />limits. <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 analyses carried out on these streams assumed an unobstructed <br />flaw condition. The flood elevations of the profiles are considered <br />valid only if the bridges and box culverts remain open, operate <br />properly, and do not fail. A couple of heavy wooden bridges could <br />conceivably be uplifted during a large flood and carried downstream <br />causing severe blockage problems. <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 />The National Flood Insurance Program encourages State and local governments <br />to adopt sound flood plain management programs. Therefore, each Flood <br /> <br />14 <br />