FLOOD10480

• County: Fremont
• Community: Canon City
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Canon City Flood Control and Drainage Analysis
• Date: 9/1/1996
• Prepared For: Canon City
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Drawings (M&I Inc. Consulting Engineers, August 1973), Canon City Whitewater Bypass and Diversion
Improvement Drawings (Taggart Engineering Associates, Inc., October 24, 1991), Flood Insurance Study.
City of Canon City, Colorado, Fremont County (FEMA, May 3, 1982), South Bank of Arkansas River Profile
(drawing prepared by Canon City, revised May 21, 1996).

The average channel width under normal flow conditions is approximately 1 00'. Existing features include
the Denver and Rio Grande Western Railroad on the northern overbank and Riverside A venue on the southern
overbank. A levee exists between Riverside Drive and the southern channel bank. The levee was constructed
by the adjacent land owner and is not recognized by FEMA. The railroad on the north side is at a higher
elevation than the existing levee on the south side. Residential developments extend throughout most of the
southern overbank of the Reach. By comparison, the northern overbank area is less developed (aerial
photography indicates scattered commercial developments).

HYDROLOGY AND HYDRAULICS

FEMA released a Flood Insurance Study (Reference 2) for Canon City on May 3, 1982. The hydrologic and
hydraulic information provided in the PIS, for the subject reach, was used in WRC's study with a few
modifications. A brief description of the significant hydrologic and hydraulic features are presented in the
following sections, However, the reader is referred to the Flood Insurance Study for a more detailed account
of these topics.

Peak discharge-frequency relationships for floods of the selected recurrence intervals (10-, 50-, 100-, and 500-
year events) were developed as part of the PIS. Table 1 presents the magnitude of flows entering the study
area, the associated return periods and related water surface elevations from the PIS report.

TABLE L
COMPUTED WA TERSURFACE ELEVATIONS FOR ..
10,50, 100, AND500YEAR.FLOOD EVENTS .
FIS HEC-2 lO-year 50-year 100-year 500-year
Section Section N2 8,850 cfs 16,500 cfs 20,500 cfs 32,200 cfs
AD 9 5327,90 5331.94 5332.77 5337.01
AE 7 5332.07 5333.79 5333.97 5340.56
AF 7.1 5332.12 5333.97 5334.44 5344.77
AG 6 5337.73 5342.19 5343.15 5345.06
AH 5 5343.31 5345.66 5347.01 5350.69
AI 4 5348.06 5350.63 5352.12 5355.04
AJ 3 5350.18 5351. 82 5352.88 5355.48
AK 2 5351.67 5353.58 5354.31 5356.46
AL 1 5356.62 5358,61 5359.33 5361. 88

The hydraulic model utilized for the PIS and this study is the HEC-2 Water Surface Profiles Package
developed by the U,S. Army Corps of Engineers Hydrologic Engineering Center (September, 1990 Version).

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