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Cross Sections Cross sections for the Arkansas River, Coal Creek, Forked Gulch, Oak Creek, Northeast Canon Drainage Area, Sand Creek, and Southeast Canon Drainage were obtained from aerial topographic mapping flown in April 1979, coupled with appropriate field verification (Reference 16). All bridges and culverts were measured in the field to obtain elevation data and structural geometry. Cross sections for Coal and Oak Creeks within the City of Florence were obtained from aerial orthophoto mapping flown in February 1977, coupled with appropriate field verification (Reference 17). Cross-sections for the backwater analyses of the various streams in the unincorporated Areas of Fremont County were field surveyed at close intervals above and below bridges and culverts in order to compute the significant backwater effects of these structures. Additional digitized cross sections were secured when the topographic maps were compiled. Locations of selected cross sections in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For stream segments in which a floodway is computed (Section 4.2), selected cross section locations are also shown on the FIRM. Water Surface Elevations Analyses of the hydraulic characteristics of the Arkansas River and the Northeast Canon Drainage Area study reach in the unincorporated areas of Fremont County were carried out by Camp Dresser & McKee, Inc. and Great Divide Engineering & Surveying, respectively. Water-surface elevations for the 10-, 2-, 1- and 0.2-percent-annual-chance floods for the Arkansas River, Coal Creek, Forked Gulch, Oak Creek, Northeast Canon Drainage Area, Sand Creek, and Southeast Canon Drainage, were computed using the USACE HEC-2 Water-Surface Profiles Program (Reference 18). For this revision, Coal Creek, Oak Creek and their associated tributaries were analyzed to provide the 1-, and 0.2-percent-annual-chance floodplains and water surface elevations of the 10-, 2-, 1-, and 0.2-percent-annual chance floods along the flow paths and channel floodway. These water surface elevations were determined by using the USACE HEC-RAS computer program and cross- sectional data provided by the City of Florence. The Coal Creek model was executed in the sub critical regime. The sub critical regime employs the downstream cross section and the slope-area method for computing the elevations for the 10-, 2-, 1-, and 0.2-percent-annual chance floods (Reference 15). Starting Water Surface Elevations Starting water surface elevations for the Arkansas River were obtained by using the slope-area method. Starting water surface elevations for the tributaries to the Arkansas River in Canon City were obtained from the Arkansas River profile at 10