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" HYDRAULIC ANALYSIS Water surface profiles of 10-, 50-, 100- and 500-year floods were computed us i ng the Army Corps of Eng i neers HEC-2 water surface profi I e computer model. The hydraul ic model (HEC-2), assumes that the hydraul ic sections such as the natural channel, channels formed by dikes or levees, bridges, cu I verts and dams are rig i d and wi I I not change due to effects of eros i on, sedimentation or debris blockage. Mann lng's "n" val ue of 0.03 was used in the channel and varied from 0.025 to 0.065 on the overbanks. Loss coefficients of 0.3 and 0.1 were used for channel expansion and contraction, respectively. Detailed printouts of input data and computed water surface elevations at each cross section are contained in Appendix B. The lOO-year elevations shown in these printouts were used to plot the lOa-year water surface profi Ie. Stream digitized cross section data was obtained from aerial photographs (Reference 3) except at bridge crossings where field data was obtained. Field notes for bridge and culvert dimensions, photographs of the stream, floodplains and bridges within the study reach are on file in COM's office. After a field check and coordination with CWCS, the road on the left overbank at cross section "0" was assumed to wash out during a major flood. A separate HEC-2 analysis was performed in this area and is contained in Appendix B. At cross sections A through F a flow spl it analysis for the lOa-year frequency was performed. Two runs were made, one through the channel and one on the south overbank, in order to establ ish the base flood elevations in this reach. Each HEC-2 run has been included in Appendix B. Contour maps with two foot intervals prepared by Ponderosa Engineering and Kucera and Associates for Fremont County and Canon City were used for plotting the lOa-year floodplain. These maps can be obtained from the Colorado Water Conservation Board, City of Canon City and Fremont County. 8