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I I I I I I I I I I I I I I 1 1 1 I I, CHAPTER V FLOOD HAZARD AREA DELINEATION a natural V-shaped section, The average channel slope is about 4%. The channel crosses Van Gordon Court in two 36" CMP culverts with the inlet projecting above ground and the outlet of the culverts crushed shut. A 48" RCP storm sewer intercepts the local stonn flows on Nevada Street and Van Gordon Court and discharges into the channel. The channel in general is not capable of carrying the 100 year flood peak, and as a result, the flood plain covers a broad area. The 10 year and 100 year flood profile have been plotted for each drainageway based on the results of the hydraulic and hydrologic analysis, The 100 year flood plain was then delineated along each drainageway. The flood plains and profiles are shown on sheets 4 to 82. Sheets 2 and 3 provide an index for these sheets. A general description of channel conditions, flooding, and flood hazards for each of the drainageways is presented below. The capacities of the various drainage facilities discussed is presented in Table 7. A, Drainageway A Drainageway A is a tributary to McIntyre Gulch at the Federal Center, draining the area southeast of Alameda Parkway. 1. Station 70+45 to 45+65, U stream Stud Limits to Van Gordon Court Sheets 4 and 5 The channel in this reach consists of a paved swale through the multi-family area. Above the multi-family area, the channel consists of Near channel station 22+00, 32+00 and 41+00, the flood will spill in shallow overflows to the east into Dakota Drive, Also, the drainageway between stations 54+00 and 66+00 generally has inadequate capacity which results in the flows entering and crossing Nevada Place. The flood hazards in this reach consist of erosion, debris removal and cleaning, interrupted traffic and services, inundation of multi- family area, and a low life hazard caused by the shallow flooding. 2. Station 45+65 to 0+00, Van Gordon Court to Confluence (Sheets 5 & 6) The drainageway in this reach consists of an improved grass- lined channel, with check drops, varying in shape from a trapeZOidal section below Alameda frontage road to a broad V-shaped section above Alameda frontage road. The average channel slope (neglecting check drops) is about 2.5%. The channel is crossed by Alameda Parkway, Union Blvd" and Alameda frontage road. The channel in general has adequate capacity to carry the 100 year peak flood, but the storm flows are separated from the main channel in several locations. Flow splitting occurs at Van Gordon Court due to the inability of the storm sewer to carry the peak flood flow, In addition, flow splitting occurs at the frontage road and Alameda Parkway (see McIntyre Gulch Flood Hazard Area Delineation report). Included in the flood hazard description is the relative life hazard for the 100 year flood, based upon flow velocity, depth areal extent, and land use. The hazard to humans within the well defined channels is fairly apparent. However, the large area of shallow flooding that occurs in the developed upper reaches of the drainageways also presents a life hazard due to high velocities of the flowing water. The residents should become familiar with these hazard areas and take the necessary precautions to avoid flowing water during periods of heavy rainfall. 10