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At Lipan Street along Sanderson Gulch, f~ows escape along the left overbank and, extend to the South Platte River as shallow flooding. These shallow flooding areas were determined using normal-depth calculations. A portion of flooding on Sanderson GJlch from South Sheridan Boulevard (State Highway 95) downstream: to cross section BQ has been labeled with a Profile Base Line. Flooding backs up at the culvert under South Sheridan Boulevard an4 flows over the road at a low spot just north of the culvert. Weir Gulch Cross section data for Weir Gulch were obtained from construction drawings (References 26-30), field survey~, and topographic mapping (Reference 56). The starting water-surface elevations were obtained assuming a simultaneous 10-year 'runoff event on the South Platte River., Roughness coefficients were determined by field inspection on the channei and overbank ar,as, and ranged from 0.013 to 0.050 and from 0.013 to 0.055,respe.cti:vely. For the channel improvements along Weirl Gulch which extend from West Alameda Avenue to Sheridan Boulevard; cross sectional data for the hydraulic analysis were taken from information prepared for the Weir Gulch project (Reference 31). Suppl~mental field observations and design information were used where needed. The starting water- surface elevations were taken from the P~eliminary Flood Insurance Study for the City and County of Denver, d~ted S~ptember 27, 1988. i All of the bridges and box culverts with~n this reach were modeled using the HBC-2 special bridge routinel in order to check for pressure flow at these structures. All qf these structures convey the 100-year discharge under pressure flQw. Manning's "n" values ranged from 0.014 to 0.035 for this reach {Reference 31). First Avenue Tributarv and Dakota Avenue Tributarv Cross section data, Manning's "n" val~es, and starting water- surface elevations were obtained from th~ 1977 UDFCD Flood Hazard Area Delineation report for the Weir Gulch tributaries (Reference 20). Cross section data were Icompiled from topographic maps (Reference 58). Starting water-:surface elevations were determined by the Weir Gulch water-surface profiles. The Manning's "n" values were 0.080 for the channel. and overbanks on Dakota Avenue Tributary and ranged from 0.025 to10.080 for the channel and overbanks on First Avenue Tributary. ' i For the drainage improvements along the! Dakota Avenue Tributary, cross sectional data for the hydraulic [analysis were taken from information prepared for the Weir Gulch! Dakota Avenue Tributary project. Supplemental field observatior\s and design information were used where needed. Improvements inf:luded a concrete culvert system which was designed taking into account manhole, bend, and 24