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. e, Flood Flows The water surface profile and flood plain for the 100-year recurrence storm are drawn on the Flood Hazard Area Delineation drawings. The computed water surface elevations at reference points are tabulated in Table 3. flooding, then the imminent riSk of flooding becomes greater. . . Flood hydrographs for the 100-year recurrence flood at various points along the channel are included as Figures 1 through 8. FLOODED AREAS Peak Flood Flows, 100-Year Flood FLOOD PROBABILITY The 100-year flood plain limits and water surface profile are shown on the Flood Hazard Area Delinea- tion Maps. The computed 100-year water surface elevation and flood plain widths at reference points are tabulated in Table 3, The following narrative describes the points where flooding occurs and the extent of the flooding, The peak flows are tabulated below at some of the major design points, Complete information on the hydrologic analysis and hydraulic calculations is available at the office of the Urban Drainage and Flood Control District, . Table 2 . Location Peak Flow (ds) 5,334 3,913 9,315 10,573 9,761 The Stream Flooding History section of this report mentions several floods that have occurred in the past. The construction of Cherry Creek Reservoir at the upper limit of this study area affords protection from flooding originating above the reservoir; however, as shown in this report, considerable damage from flooding can be expected to occur from rainfall in the study reach of this report. a, Points of Flooding . Goldsmith Gulch at Cherry Creek Cherry Creek above Goldsmith Gulch Cherry Creek below Goldsmith Gulch Cherry Creek at First Avenue Cherry Creek at South Platte River ( 1l Station 10 + 00 to 24 + 00 - The 100-year water surface in this section is one to two feet over the channel banks due to con- strictions caused by the existing railroad bridges, . HYDRA ULIC ANALYSIS The 100-year flood event has a one percent chance of being equalled or exceeded during any year, and it is inevitable that a rainfall great enough to cause this amount of runoff will occur, As develop- ment takes place within the drainage basin causing an increase of runoff, and possible encroachment into storage areas and drainage channels, and as a lack of maintenance decreases the channel flow capacity and increases the amount of refuse and debris within the channel which will block drainage structures in time of ( 2) Station 40 + 00 to 46 + 00 - The water surface is approximately one foot over the banks in this section by the Lawrence and Arapahoe Street bridges. a 41 Hydraulic analysis was performed in order to determine the water surface elevations for the 100- year storm, The water surface profile was compiled using the Corps of Engineers' HEC-2 computer pro- gram. Channel cross section data was taken from I" = 100' scale, 2-foot contour topographic maps, Channel roughness factors and bridge areas and coefficients were Obtained from field investigations, ( 3) Station 62 + 00 to 64 + 00 - Flooding occurs in this section to a depth of one foot above the Colfax Avenue bridge, ( 4) Station 90 + 00 to 100 + 00 - The water floods over Speer Blvd, into the Sunken ~ 5 "