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<br />At Lipan Street along Sanderson Gulch, flows escape along the left <br />overbank and extend to the South Platte River as shallow flooding. <br />These shallow flooding areas were determined using normal-depth <br />calculations, <br /> <br />A portion of flooding on Sanderson Gulch from South Sheridan <br />Boulevard (State Highway 95) downstream to cross section BQ has <br />been labeled with a Profile Base Line, Flooding backs up at the <br />culvert under South Sheridan Boulevard and flows over the road at a <br />low spot just north of the culvert, <br /> <br />Weir Gulch <br /> <br />Cross section data for Weir Gulch were obtained from construction <br />drawings (References 26-30), field surveys, and topographic mapping <br />(Reference 56). The starting water-surface elevations were <br />obtained assuming a simultaneous 10-year runoff event on the South <br />Platte River" Roughness coefficients were determined by field <br />inspection on the channel and overbank areas, and ranged from 0.013 <br />to 0.050 and from 0,013 to 0,055, respectively. <br /> <br />.. <br /> <br />For the channel improvements along Weir Gulch which extend from <br />West Alameda Avenue to Sheridan Boulevard, cross sectional data for <br />the hydraulic analysis were taken from information prepared for the <br />Weir Gulch project (Reference 31), Supplemental field observations <br />and design information were used where needed. The starting water- <br />surface elevations were taken from the Preliminary Flood Insurance <br />Study for the City and County of Denver, dated September 27, 1988, <br /> <br />All of the bridges and box culverts within this reach were modeled <br />using the HEC-2 special bridge routine in order to check for <br />pressure flow at these structures. All of these structures convey <br />the 100-year discharge under pressure flow, Manning's "n" values <br />ranged from 0.014 to 0,035 for this reach (Reference 31), <br /> <br />First Avenue Tributarv and Dakota Avenue Tributarv <br /> <br />Cross section data, Manning's "n" values, and starting water- <br />surface elevations. were obtained from the 1977 UDFCD Flood Hazard <br />Area Delineation report for the Weir Gulch tributaries <br />(Reference 20). Cross section data were compiled from topographic <br />maps (Reference 58), Starting water-surface elevations were <br />determined by the Weir Gulch water-surface profiles, The Manning's <br />"n" values were 0,080 for the channel and overbanks on Dakota <br />Avenue Tributary and ranged from 0,025 to 0.080 for the channel and <br />over banks on First Avenue Tributary, <br /> <br />For the drainage improvements along the Dakota Avenue Tributary, <br />cross sectional data for the hydraulic analysis were taken from <br />information prepared for the Weir Gulch Dakota Avenue Tributary <br />project, Supplemental field observations and design information <br />were used where needed. Improvements included a concrete culvert <br />system which was desi-gned taking into account manhole, bend, and <br /> <br />24 <br />