M3 Engineering performed a Comprehensive Stormwater Master Plan and an economic analysis for 20 square miles in the City of St. Charles, MO. The purpose of the study was to recommend flood mitigation measures, prioritize stream restoration and determine whether there are steps the City can take to improve water quality in streams.

FLOOD MITIGATION – The Flood Mitigation effort began with a review of flood complaints and a field inventory of structures known to flood. GIS and XP-SWMM 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. A risk-based analysis is being used to determine the level of improvement that is consistent with the City’s goals and budget. The proposed measures will be prioritized based on a rating system developed in conjunction with City staff.

STREAM RESTORATION – M3 inspected and evaluated approximately 20 miles of stream using Rapid Geomorphic Assessment techniques. M3 developed a GIS tool that will forecast the ultimate stream configuration and developed a cost per stream-foot to address the degradation. The proposed improvements were then prioritized for use in the City Stream Capital Improvement Program.

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 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.

M3 prioritized the implementation of the projects using benefit-cost ratios and an economic analysis that identified the ideal investment level based on the point of diminishing rate of returns.