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<br />(Exhibi t 2). Due to overbank spli t flows, a floodway along the <br />South Platte River was not delineated. <br /> <br />Water-surface elevations of floods of <br />intervals were computed through the use <br />backwater computer program (Reference 46). <br /> <br />the selected recurrence <br />of the COE HEC-2 step- <br /> <br />A brief discussion of the hydraulic analysis of each stream studied <br />by detailed methods follows: <br /> <br />Clear Creek <br /> <br />Cross section data, Manning's "n" values, and starting water- <br />surface elevations were obtained from the 1979 UDFCD Flood Hazard <br />Area Delineation report for Clear Creek (Reference 22). Cross <br />section data for the HEC-2 analysis were compiled from topographic <br />mapping (Reference 47). Typical roughness or Manning 's "n" values <br />used were 0.025 to 0.045 for the channel and 0.040 to 0.075 for the <br />overbank areas. <br /> <br />Bear Creek <br /> <br />Cross section data, Manning's "nit values, and starting water- <br />surface elevations- were developed for u.se in the 1979 UDFCD Flood <br />Hazard Area Delineation report for Bear Creek (Reference 48). <br />Cross section data were obtained photogrammetrical1y by digitizing <br />cross sections marked on aerial photographs of the stream channel <br />and floodplain (Reference 49). The digitized cross sect ion data <br />were supplemented with cross sections taken from topographic <br />mapping (Reference 50) developed from the aerial photography. All <br />bridge cross sections were obtained from actual field measurements. <br />Roughness coefficients for the channel and overbank areas were <br />estimated by field inspection of the study area. Manning's "n" <br />values were 0.035 in the channel and from 0.025 to 0.090 in the <br />overbank areas. <br /> <br />Additional cross sections were <br />plans due to recent grading <br />vicinity of Lowell Boulevard. <br /> <br />included from channel improvement <br />and channel improvements in the <br /> <br />Cherry Creek <br /> <br />Cross section data, Manning's "n" values, and starting <br />surface elevations were obtained from the 1976 UDFCD Flood <br />Area Delineation report for Cherry Creek (Reference 10). <br /> <br />water- <br />Hazard <br /> <br />Revised cross sections reflecting recent channel improvements in <br />the areas of Bannock Street to First Avenue were obtained from the <br />Wastewater Management Division of the Denver Department of Public <br />Works Cherry Creek channel improvements reports (References 51 <br />and 52). <br /> <br />21 <br />