FLOOD10499

• County: Fremont
• Community: Canon City
• Stream Name: Fourmile Creek
• Basin: Arkansas
• Title: Canon City / Fourmile Creek Documents
• Floodplain - Doc Type: Correspondence

. The ENGINEER shall meet initially and periodically thereafter with the CITY and/or
the CWCB to ensure compliance with the Scope of Work, to discuss pertinent
technical and administrative issues, to procure existing information related to the
work, and to review work-in-progress.

. The ENGINEER shall incorporate the REVISED MAPPING into, and will supersede
the affected portions of the ORIGINAL MAPPING in order to creatl3 a new
topographic mapping (NEW MAPPING) for the STUDY REACH.

. Hydrologic analyses shall NOT be performed for this STUDY. Existing hydrologic
information on Fourmile Creek has already bE~en developed by the BRCS for the
10-, 25-, 50-, 100-, and 500- year frequencies. This information is acceptable to the
CITY and the CWCB.

. Field investigations shall be made by the ENGINEER to verify and check the
accuracy of the NEW MAPPING, to inspect the floodplain area of thEl STUDY
REACH, and to assess hydraulic structures" existing development, cultural and
topographic features, and other channel/overbank conditions for the purpose of
revising modeling parameters and assumptions as needed.

. Hydraulic analyses shall be performed by the ENGINEER and based on the
standard step backwater method used by the U.S. Army Corps of Engineers HEC-2
computer model. Hydraulic calculations shall be performed to derive water surface
profiles for the 10-, 25-, 50-, 100-, and 500-.year flood frequencies and shall be
presented to the CITY for approval upon completion. These calculations shall be
complete to the extent of attaining, at the least, the capacity and general condition of
the existing channels, conduits, bridges, embankments, floodplain areas, and
localized depressions. Analyses and assumptions shall be in conformance with
FEMA and CWCB standards and guidelinE!s. Bridges and culverts shall be
considered for debris blockage, as appropriate, and analyzed accordingly. The
existing HEC-2 input files, as developed by the NRCS, shall be used as the basis for
the hydraulic analyses. All HEC-2 cross-section information, roughness values,
contraction and expansion coefficients, bridge information, reach lengths, and other
input parameters shall be reviewed by the ENGINEER and revised as necessary.

. Determination shall be made for a 100-year floodway on Fourmile Creek from its
confluence with the Arkansas River upstream to the south side of U.S. Highway 50.
The f100dway shall be based on encroachment resulting in a maximum increase in
the water surface elevation of 1.0 feet. Encroachment and conveyance
assumptions shall follow FEMA guidelines and specifications. A previous floodway
analyses was not performed by the NRCS.

. The following information shall be depicted for the STUDY REACH by the
ENGINEER using the NEW MAPPING as a base map:

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