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<br /> TABLE 1. SUMMARY OF DISCHARGES (Cont'd) <br /> Peak Discharges (cubic feet per second) <br /> Drainsge Area 10- 50- 100- 500- <br />Stream Name and Location (square miles) Year Year Year Year <br />South Cotton Creek <br />Confluence at Big Dry Creek 0.19 46 113 140 265 <br />Upstream Study Limit 0.10 35 90 113 221 <br />North City Park Creek <br />Confluence with 0.14 29 85 107 230 <br />Big Dry Creek <br />Upstream Study Limit 0.04 19 55 65 180 <br />South City Park Creek <br />Confluence with Big Dry Creek 0.09 20 54 68 138 <br />Upstream Study Limit 0.02 10 30 40 88 <br /> <br />Cross sections used in the backwater analyses for all streams were <br />obtained by aerial photogrammetry (Reference 10). The below water <br />sections of all cross sections were obtained by field measurement. <br />All bridges, dams and culverts were field surveyed to obtain <br />elevation data and structual 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 Insurance Rate Map <br />(Exhibit 2). <br /> <br />Roughness factors (Manning's "n") used in the hydraulic <br />computations for the study streams were chosen by engineering <br />judgment and based on field observations of the flooding sources <br />and floodplain areas. Roughness values for the main channels of <br />the streams studied range from 0.02 to 0.065 with floodplain <br />roughness values ranging from 0.02 to 0.10. <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. The results obtained from the HEC-2 program were <br />adjusted in the vicinity of bridges to more accurately represent <br />actual flooding conditions. Starting water-surface elevations were <br />based on hand calculations at control sections; obtained by the <br />slope area method, or determined for a tributary to a major stream <br />from the major stream at concurrent flows. <br /> <br />The hydraulic analyses for this study were 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 />9 <br />