April 26, 2010
After flooding caused by the remnants of Hurricane Ike in 2008, the City of St. Charles, Missouri asked Terra Technologies to design stream bank stabilization measures for four different locations within the City in order to prevent potential property damage. The projects are located along portions of Boschert Creek and Cole Creek.
Erosion has been occurring near residences built close to urban streams. Upstream development has increased the volume of storm flows in the streams and the stream geometry is changing to match the new hydrologic conditions.
Terra Technologies took a biotechnical engineering approach to bank stabilization and considered the geomorphic stream characteristics, hydraulics and hydrology, watershed conditions, geotechnical soils analysis, and our previous experience on similar stream systems. As a result, the design approach for each project varied according to the different site conditions. The design consisted of a combination of toe armoring, grade control, bank stabilization, and ecological restoration. Gabion baskets will be used to stabilize stream toes and stream banks in their present location, angular rock weirs will provide grade control, and high tensile turf reinforcement matrixes, erosion control blankets and the roots of native vegetation will stabilize the stream bank slopes. On one project site, bank stabilization measures were not practical and a pipe culvert was extended upstream to enclose the area of instability.
In addition to the designing the projects, Terra Technologies guided the City of St. Charles through the Clean Water Act Section 404 and 401 permitting process necessary to authorize the water quality impacts caused by the bank stabilization activities. Hydraulic analyses were also performed in order to determine that the projects would not increase the 100-year flood water elevation as the projects are within floodways regulated by FEMA.
Construction of the projects is expected to begin in 2010.