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<br />Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of the flooding source in Clark <br /> <br />and Glen Eden were carried out to provide estimates of the elevation of the <br /> <br />100-year flood along the flooding source studied. <br /> <br /> <br />For the backwater analyses, 12 cross sections were obtained from field <br /> <br />survey and 27 were synthesized. The synthesized cross sections were estimated <br /> <br />from adjacent surveyed cross sections and topographic maps. Structural <br /> <br />geometry and elevations for two bridges and road sections were also obtained <br /> <br />from the field survey. The locations of the cross sections used in the back- <br /> <br />water analysis are shown on the flood profile and map. Cross sections were <br /> <br />located upstream and downstream from bridges in order to compute the backwater <br />effects of those structures. Since many of the synthetic cross sections were <br /> <br />very close to each other. only selected cross sections. those at breaks in <br /> <br />water-surface slope, were labeled with a prime (') superscript. <br /> <br />Channel roughness factors (Manning's "n") used in the hydraulic <br /> <br />computations were determined by engineering judgment based on field <br /> <br /> <br />observations of the flood-plain areas and by using prediction equations <br /> <br /> <br />developed by Jarrett (1985). Roughness values averaged 0.057 for the channel <br /> <br /> <br />and ranged from 0.040 to 0.090 for the overbank areas. <br /> <br />Wate~-surface elevations for the 100-year flood were computed by WSPRO. a <br /> <br /> <br />step-backwater computer program developed by the U.S. Geological Survey for <br /> <br /> <br />the Federal Highway Administration (Shearman and others, 1985). <br /> <br />3 <br />