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The starting water-surface elevation was set at critical depth for Clear Creek and Lena, Apex, and Jackson Gulches. For all other stream reaches, the slope-area method was used to begin the backwater calculations. Flood profiles were drawn showing computed water-surface elevations to an accuracy of 0.5 foot for floods of the selected recurrence intervals (Exhibit 1). On Clear Creek, water-surface elevations were computed based on results from the Gingery and Associates, Inc., study (Reference 17).. These results were modified at Ford Street and downstream through the Coors brewery, where the topographical configuration has changed. At Ford Street, for example, the channel and overbank flows were handled separately. The resulting water-surface eleva- tions in the channel at Ford Street and Washington Avenue were input to the HEC-2 model considering only the channel as an effective flow area and modifying the discharges accordingly. The 50- and SOD-year flood water-surface elevations were extrapolated from the 10- and 100-year flood elevations. Other changes have been made to the Gingery and Associates, Inc., study, with UDFCD approval, upstream of U.S. Highway 6. The 50- and SOD-year flood water-surface elevations were not computed for Cressmans Gulch, Cressmans Gulch Old Channel, Tucker Gulch, Kenneys Run, East Fork Kenneys Run, West Fork Kenneys Run, West Fork Kenneys Run Tributary No.1, North Fork of West Fork Kenneys Run Tributary No.1, West Fork Kenneys Run Tributary No.2, and Deadman Gulch. The analyses carried out on these streams assumed an unobstructed flow condition. The flood elevations of the profiles are considered valid only if the bridges and box culverts remain open, operate properly, and do not fail. A sensitivity analysis was conducted to determine the effect of obstructing the a-foot-diameter culvert that carries the low flows of Kenney Run. The computed water- surface elevations were not significantly affected by even a 100 percent obstruction of the culvert for the range of flood discharges used in this study. On Apex Gulch, spillage onto the overbank areas results in shallow 100-year flooding. This shallow flooding was determined using engineering judgment. Along South Golden and Jackson Streets, between East Fork and West Fork Kenneys Run, floodwater being forced over streets becomes hydraulically disconnected from the channel with the streets acting as drainageways. Flows exceeding street capacities have been designated as Zone AD (Depth 1 foot) and will threaten residential properties in this area. 16