FLOOD10235

• County: Fremont
• Community: Canon City
• Stream Name: Arkansas River & Tributaries
• Basin: Arkansas
• Title: Hazard Mitigation 404 Grand Application for FEMA - Includes 3 Maps
• Date: 2/1/1998
• Prepared For: FEMA
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Collecting stormwater flows at the hogback openings and transporting these flows in pipes and
channels to upsized city collection system elements is also possible, but expensive. Further,
sediment and debris would still have to be removed from storm flows before entering any pipes.
Sedimentation basins at the hogback openings would, therefore. still be required. Thus, because
of high cost this concept was also discarded.

Selection of Preferred Alternative

Costs. Each of the analyzed flood mitigation alternatives has costs associated with it. For the
Partial and Full Detention Alternatives, these costs are a function of initial construction and
annual maintenance costs for flood control structures and of post-flood clean-up costs. For the
No Action Alternative, costs are a function only of the magnitude of cleanup and repair work
required after storm events.

Initial construction costs for the Partial and Full Detention Alternatives have been previously
presented in Tables II-3 and II-6. Maintenance costs associated with the ponds are assumed to be
composed mainly of occasional repairs to rip rap lining and periodic removal of accumulated
sediment deposits in the ponds and obstructions to pond outlet pipes. Hourly costs for equipment
and personnel to execute maintenance work were provided by the Canon City Public Works
Department. Computed annual maintenance costs assume that a backhoe, a dump truck, two
operators and a laborer will be required an average of two days per year for the Partial Detention
Alternative and three days per year for the Full Detention Alternative. Based on these equipment
and personnel assumptions, the estimated cost for maintenance of all seven ponds on a per day
basis is $850 (1998 dollars). Post-flood clean-up costs were also included in the analysis of
benefits and costs. For the Partial Detention Alternative, clean-up and repair costs were taken to
be 25 percent of the annual No-Action cost of $52,920. This is based on an assumption that the
ponds will have a 75 percent sediment trap efficiency. For the Full Detention Alternative, post-
flood clean-up and repair costs have been taken to be zero based on the assumption that
essentially all sediment will be removed by the ponds. No escalation of clean-up or maintenance
costs over time has been considered.

In order to compute the present worth of costs associated with the No Action Alternative, a
design life of 50 years has been assumed for the proposed detention ponds. The present worth of
the No Action Alternative has been based on this design life, average annual costs for cleanup
and repairs reported by the City and an assumed discount rate of 7 percent. No escalation of
clean-up or maintenance costs over time has been considered.

Benefits. The No Action Alternative does not mitigate any future flood damage but does provide
the benefit of no environmental disturbance. Attaching a dollar value to this benefit is difficult
especially before completion of the environmental review process. Because of this difficulty,
environmental disturbance has not been included in the analysis of benefits and costs.

The Partial and Full Detention Alternatives have the benefit of avoiding post-flood cleanup and
repair costs. In addition to the quantifiable flood mitigation benefits, the two detention

II-5