St. Charles, Missouri
Client:
City of St. Charles
Terra Technologies was retained by the City of St. Charles to perform stabilization of Cole Creek from No. 9 Green to Berlekamp Drive. Storm water flow was discharged through a natural stream channel en route to a corrugated metal pipe culvert beneath Berlekamp Road. Scour hole formation and ponding was present in the upper two-thirds of the project area and was contained by a series of major sediment point bars near the culvert. The entire project was laterally encroached by residential lawns and pre-project bank armoring includes rock blanket, tie-wall, and concrete retaining wall structures, all of which existed in varying degrees of failure. The opposite bank was less severely encroached and appeared geomorphically and biologically stable, with the exception of the area around the roadway culvert. A portion of the base stream flow appeared to undercut the culvert.
Terra Technologies performed a geomorphic evaluation of the stream channel. The portion of the channel closest to the existing corrugated metal pipe was found to be unstable with steep slopes, failing retaining walls and limited room for natural or soft armoring solutions. The most appropriate alternative in this area was to extend the 11’ diameter pipe approximately 250 upstream to where the slopes were fairly stable with a shorter slope length and much lower grade. A Hercules plantable face retaining wall was installed at the headwall of the pipe.
Upstream of the piped segment, individual areas of instability required stabilization. In addition, a detention basin at the upstream end of the project reach had failed and was no longer functioning as originally designed and constructed.
Bank stabilization in areas with minor geotechnical instability included a double-stack gabion toe while other areas only required a coir log toe to maintain the stream‘s flow line. All areas of the project received native seeding and containerized plants including areas outside of the disturbed areas in order to enhance the biological integrity of the entire riparian corridor. The detention basin was regraded with improvements to the overflow structure and the area was planted with appropriate native wetland vegetation.
The project was constructed in the summer and fall of 2007.
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