TheCity of Saint Charles retained Intuition & Logic to perform a flood reduction feasibility study along Marie Drive and Elm Street.  The intersection and one adjacent house are subject to frequent flooding from the confluence of East Cole Creek and an unnamed tributary.  The City had purchased the property as part of a flood buyout program and wanted to know if excavating a detention structure during the home demolition would have a positive cost/benefit for localized flood reduction. 



Our analysis evaluated several possible flood control works: improvements to the flood control channel as well as offline detention storage.  We performed the analysis using the USACE’s recent model of the Dardenne Creek Watershed.  Using GeoHEC-RAS and the City’s current GIS data, we were able to quickly add the local conditions and proposed improvements to the model, which included adding the unnamed tributary and culvert crossing at the confluence. 



We found that the site’s limited storage potential combined with the backwater effects from the adjacent confluence yielded minor positive benefits for reducing peak flood elevations.