M3 Presents at Missouri APWA conference in Columbia, MO

Marc Eshelman of M3, along with Kevin Corwin and John Reeves of the City of St. Charles, presented the results of the St. Charles Stormwater Management Plan at the Missouri APWA conference in Columbia, MO on November 9, 2015. The presentation was titled A Sensible Approach to Flood Mitigation, Stream Restoration and Water Quality. Following is the description presented to the APWA Conference Committee: The City of St. Charles, MO, located at the confluence of the Mississippi and Missouri Rivers, faces challenges associated with flooding, stream degradation and renewing their NPDES Water Quality Permit. The City chose to address these challenges using a managed-risk approach to create integrated solutions that became part of their Capital Improvement Plan. The effort was accomplished using a variety of technologies, including hydraulic modeling and custom GIS analytical tools. FLOOD MITIGATION – The XP-SWMM hydraulic model was used to model both the open channel and enclosed systems in order to identify the root causes of flooding and to model alternatives to mitigate it. Damage curves were created that defined the cost of flood damage at different elevations. The cost of mitigation measures was then compared to the resultant flood damage reduction in order to identify benefit cost (B/C) ratios for various projects. Flood mitigation projects that also helped to address stream degradation and/or improved water quality received additional benefit points. STREAM RESTORATION – Approximately 20 miles of stream were evaluated using Rapid Geomorphic Assessment techniques. Forecasted property damage cost due to stream degradation was compared to the cost of stabilization measures in or order to identify B/C rations for various projects. Stream degradation projects that also helped to address flood mitigation and/or improved water quality received additional benefit points. Developing B/C ratios allowed both flood mitigation and stream restoration projects to be integrated into a single prioritized Capital Improvement Program. All the projects were plotted using their B/C ratios in order to locate the “knee of the curve”, or point at which proposed projects begin to show a diminished rate of return on capital investment. Projects on the positive side of the “knee of the curve” were recommended for construction. WATER QUALITY – M3 developed a GIS Tool that processes the soils, slope, land use, ground coverage and other pertinent environmental information for each Watershed to determine locations that may contribute to water quality degradation in the streams. M3 characterized each watershed using the GIS Tool and highlighted “hot spots”, or locations that exhibit a high potential for contributing to water quality degradation. Recommendation for improving water quality were developed based on the analysis.   This presentation will describe a defensible approach to developing and prioritizing flood mitigation and stream restoration projects based on acceptable risk and cost to municipalities.