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Cross section information used in this analysis was taken from construction drawings, as-built drawings, field surveys and fra!'. the twJ-foot contour interval, 1"-100' scale, topographic mapping (Reference 5) from the major drainageway planning report. In many cases, the cross sections were compiled using a combination of the construction drawings and the mapping, or the as-built drawings plus the mapping. A summary listing the source of cross section data for specific channel reaches is provided in Table 4. I I I I I I I I I I I I I I I I I I I TABLE 4 Cross Section Data Source Location SANDERSON GULCH South Platte River to C&S Railroad C&S Railroad to Arkansas Avenue Arkansas Avenue to Federal Boulevard Federal Boulevard to Tennyson Street Tennyson Street to Sheridan Boulevard Bi t-O-Sea Reservoir and Wads,.,orth Boulevard to Kendrick Reservoir Bit-O-Sea Reservoir to Wadsworth Boulevard NORTH SANDERSON GULCH Sanderson Gulch to Pierce Street pierce Street to Garrison Street (Reference 6) was used to show the effect of South Platte River backwater up Sanderson Gulch. For North Sanderson Gulch, the starting water surface elevation was taken from the Sanderson Gulch profile. Roughness coefficients were estimated after field investigation of the study reaches. The range of values used in this study are given in Table 5. TABLE 5 Manning's Roughness Coefficients Field Surveyed Lower Sanderson Gulch Drainage Improvements Construction Drawings Upper Sanderson Gulch Drainage Improvements As-Built Drawings Field Surveyed and Topographic Mapping (Reference 5) Upper Sanderson Gulch Drainage Improvements As-Built Drawings City of Denver, 1978 Sanderson Gulch Drainage Improvements As-Built Drawings, Urban Drainage and Flood Control District, and City of Lakewood, 1976 Channel ---- .015 - .060 Overbank --- .035 - 0.1 The 100-year floodplain limits are shown on the Flood Hazard Area Delineation Map Drawings (Sheets 4 - 19). The flood profile is drafted on the separate profile sheets, PI - P8. Water surface elevations are tabulated for each cross section in Tables 6 and 7. All hydraulic calculations developed during this study, including copies of computer runs, are available at the Urban Drainage and Flood Control District. Floodway Field Surveyed A floodway was determined only for study reaches on Sanderson Gulch within the City of Denver. This information was developed during the course of the Denver Flood Insurance Study. The flood- way criterion used is dependent only upon the depth of flow on the floodplain. AreaS with flow depths exceeding 18 inches are with- in the floodway. Areas with flow depths less than 18 inches are termed flood fringe or low hazard areas. Table 6 lists floodway widths and floodway locations for Sanderson Gulch in Denver. Field Surveyed Sanderson Gulch Drainage Improvements North Sanderson Gulch As-Built Drawings, Urban Drainage and Flood Control District, and City of Lakewood, 1977 Floodways are generally determined to indicate high hazard areas or areas subject to significant damage during a large flood event. The starting water surface elevation on Sanderson Gulch was determined using the Valley Road stream crossing as a control. Flood elevation data for the 100-year event from the Corps' recent floodplain study (5)