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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Case A duplicates the effective PIS HEC-2 model. After observing some discrepancies with the placement
of encroachments for several sections, WRC coded a corrected duplicate effective file (Case B) which was
then used as a basis for subsequent modifications.

Case C incorporates the City's intake diversion weir and whitewater by-pass into the HEC-2 model by adding
data for three new channel cross sections. Section 2.2 (located at the crest of the weir) and Section 2.3
(located 33 feet downstream of the weir) were based on information presented in the Whitewater Bypass
construction drawings (Reference 5). Section 2.1 (located 50 feet upstream of the weir was based on
extrapolated information from the next downstream PIS-surveyed cross section (PIS designation AJ; HEC-2
Section 3.0). The locations of these new sections in relation to the original PIS sections are shown in Exhibit
B. Left and right channel overbank information for all three sections was extrapolated from section 3.0. Data
from drawings of the City's recent survey of the existing levee (Reference 6) on the southern bank was also
incorporated into the new and original cross sections where applicable.

Cases D and E include coding encroachments in the HEC-2 models to simulate the railroad embankment and
a levee on the south bank to contain the lOa-year flow. The effect of adding encroachments to the southern
bank and the railroad embankment on the north without modeling the diversion weir (Case D) raises the
surface water elevation 1.9 feet above the FIS water Surface elevations. Modeling the diversion weir (Case
E) raises the water surface elevation another 3.1 feet at section 2.0. The Case E water surface elevation at
section 2.0 is higher than the railroad embankment north of the river. Thus, modeling the weir with a levee
on the south bank to contain the lOa-year flow has the effect of expanding the lOa-year floodplain north of
the river.

ALTERNATIVES ANALYSIS

WRC performed a conceptual level investigation of alternatives for the containment of the lOa-year flood
event which included:

1) The widening of the channel and diversion weir to reduce the 100-year water surface elevation.

2) The re-construction of an earth levee system on the north and south banks beginning at section 4.0
and extending 2,723 feet upstream to section 1. O. The levee dimensions were designed to conform
with FEMA levee design requirements. Levee protection for the northern bank would be required

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