FLOOD10417

• County: Mineral
• Community: Mineral County
• Stream Name: Willow Creek
• Title: Willow Creek Channel Improvement, Mineral County, Colorado - Channel Replacement Feasibility Report
• Date: 8/13/2003
• Prepared For: Willow Creek Reclaimation Committee
• Prepared By: Chou Cha, P.E., Civil Engineer
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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5. DEMOLITION

Any replacement option will require demolition ofthe existing hand-placed grouted stone
channel. The demolition as mentioned above would require equipment time, labor,
hauling of the debris and disposing ofthe material. The waste material could be utilized
in other places by the town of Creede in an effort to cut cost. If the material rubbles are
not stockpiled and used by the town, disposal fees would be added. The estimated field
cost for demolition is $274,000 without the contractor disposing the material. This cost
includes hauling by the contractor to stockpile the material at the airstrip area that is,
about two miles from the project site.

The demolition material can be used for fill materials or riprap side slope protection for
areas upstream and downstream of the existing channel. Due to potential aggregate and
cement reaction as reported by past inspection reports, recycling the larger stone by
crushing into smaller rock for aggregate for new lining concrete is not recommended
without testing.

6. DESIGN ALTERNATIVES

The design alternatives considered are existing trapezoidal channel shape, rectangular
channel shape, partially full flowing pipes, and partially full flowing covered concn::te
box culvert. Each design alternative will be presented with its advantages and
disadvantages. Their construction cost estimates will also be presented along with the
demolition cost estimates and are included in Appendix B.

Due to limited construction easements and right of ways, all proposed alternatives
assume the existing horizontal alignment of the channel. Some of the alternatives may,
however, have varying slope in the flow direction to accommodate the different channel
sections. The open top channel alternatives will be reinforced concrete. The two
construction options for these alternatives will be either a cast in place concrete or precast
concrete construction. Cast in place concrete construction refers to the yontractor
forming the channel to the dimensions as designed and concrete being placed in the field,.
Precast concrete construction will involve the forming and placing of the concrete in the
controlled environment of the contractor's facility off site and the pieces being delivered
for installation. Both of these methods are driven by cost to the contractor. Precast
construction is allowed as a method of construction ifthe contractor provides the
adequate design submittals for review. Specification paragraphs can allow such a
construction proposal if the contractor feels that there would be cost savings to the
WCRC and the contractor.

For the purpose of this report a cast in place. construction method was cost estimated and
presented here for the two open top alternatives. Concrete forms imitating the shapes of
hand placed stone could be formed on all exposed concrete surfaces as shown in Figure 4.
This would resemble the existing channel and present an aesthetic pleasing look. For the
pipe alternatives, different materials will be evaluated on their availability at the larger

NRCS Northern Plains Engineering Team 5