FLOOD10499

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

engineering/floodplain information developed during this STUDY should be presented in a clear
and professional fashion as it may be used in developing a master drainage plan, in road and
bridge planning and design, and design of channel modifications and flood control features. The
finished product must be in compliance with the CWCB's "Rules and Regulations for the
Designation and Approval of Floodplains and of Storm or Floodwater Runoff Channels in
Colorado and FEMA's "Guidelines and Specifications for Study Contractors."

Specific Description of Work Items
The CITY and the CWCB shall obtain all existing reports, digital computer models, and
technical backup information from the NRCS and provide it to the ENGINEER at the onset of
the STUDY. The ENGINEER will also be provided digital copies of the topographic mapping
used in the NRCS study (ORIGINAL MAPPING) as well as the revised topographic mapping
(REVISED MAPPING) for the affected portions of the STUDY REACH.

I) 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.

2) The ENGINEER shall incorporate the REVISED MAPPING into, and will supersede the
affected portions of, the ORIGINAL MAPING in order to create a new topographic mapping
(NEW MAPPING) for the study reach.

3) Hydrologic analyses shall NOT be performed for this STUDY. Existing hydrologic
information on Fourmile Creek has already been developed by the NRCS for the 10-, 25-,
50-, 100-, and SOO-year frequencies. This information is acceptable to the CITY and the
CWCB.

4) Field investigations shall be made by the ENGINEER to verify and check th~: accuracy of the
NEW MAPPING, to inspect the floodplain area of the 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.

5) Hydraulic analyses shall performed by the ENGINEER and based on the standard step
backwater method using 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 SOO-year flood frequencies and shaH 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 existing channels, conduits, bridges, embankments,
floodplain areas, and localized depressions. Analyses and assumptions shall be in
conformance with FEMA and CWCB standards and guidelines. 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

2