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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During their construction of the existing channel, the Corps designed a temporary bypass
flume and ditch that; ran along part of Creede Avenue, Cliffe Street, and La Garita Street.
Today the construction of such a flume and ditch will be very expensive and would raise
multiple issues for the community. It would require the road shoulders and road
crossings to be excavated and repaired to its existing condition. Access to homes and
driveways would be' another problem. The bypass ditch used during the Corps' design
and construction had a 5 feet bottom width with 1 Y2 to 1 side slopes and was 3 feet deep
and included an elevated steel flume section.
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The bypass proposal that is estimated for this alternative includes the construction of
upstream temporary: dams and pumping of the water to a location downstream of thle
section being constrUcted. The length of bypass pumping could range between a couple
of hundred feet and up to a thousand feet long. The pumps would need to run 24 hours a
day and 7 days a week until the construction of each segment is finished. The pumps
estimated for this alternative include sound attenuation enclosures that will reduce the
noise level to about 30 decibels. Once one segment of the construction is completed the
bypass system is moved downstream to another section and so on until the construction
ofthe project is completed. The temporary dam setup could be a proprietary system
designed and installbd by commercially known subcontractors or could be designed by
the contractor by th~ir registered engineer.
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The cost ofthis alterinative is estimated at $3,120,000 and includes the temporary dams
and pump water bypass system as mentioned above, but excludes appurtenances.
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6.2 ALTERNATIVE 2 - RECTANGULAR CHANNEL SHAPE
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This rectangular channel alternative would include reinforced concrete for the lining
material. A general drawing ofthis alternative can be referenced in Figure A3 in
Appendix A. The options of either a cast in place or precast system should be considered
and as mentioned above are driven by the cost savings to the contractor. This alternative
has the following advantages and disadvantages..
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A rectangular channel is considered due to its smaller cross-sectional width. This allows
for some access duripg construction within the rights of way. The rectangular section
would provide working space to either side of the channel. This working space coulld be
utilized to install a water bypass system for Willow Creek inside this right of way. The
bypass system will c'onsist of a temporary dam upstream of the immediate construction
area with a pipe or pipes running along the trench of the channel. The pipes will convey
the water downstream of the construction section. This is cost effective because the pipe
flow is driven by gr~vity. The process will repeat until the channel is fully constructed.
Construction of a se<:tion of several hundred feet would be appropriate and the pipe could
be sized to a reasonable flow. The rectangular channel width is sized to approximatdy
the same dimensions as the original timber chute. This is referenced from the Corps of
Engineer's construction drawings showing cross sections from station 18+65 to 20+02
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NRCS Northern Plains Engineering Team 7