St. Charles' 7th Avenue Creek Flood Reduction and Stream Restoration

The 7th Avenue Creek traverses from east to west through the heart of St. Charles and provides an amenity to the residents that live along the creek. The 2008 flood event far exceeded the limits of the mapped 100-year flood boundaries of the 7^th Avenue Creek regulatory Flood Insurance Rate Maps (FIRM).

FEMA prepared a revised Flood Insurance Study (FIS), which resulted in flows increasing by approximately 250% and the 100-year Base Flood Elevations (BFE) increasing by almost 3 feet. Approximately 118 properties (residential and commercial) were impacted by the revised floodplain maps, including newly mapped properties in the floodplain.

Significant portions of the creek were also highly channelized and eroded, with riparian areas in poor condition as a result of urbanization. The City hired HR Green to help with preparing a Master Plan to mitigate the impacts of the newly mapped floodplain while achieving multi-faceted benefits of reduced property impacts, economic redevelopment, and improved water quality.

The 7th Avenue Creek Master Plan identified a phased approach to reduce the 100-year floodplain along the 2-mile stretch of 7th Avenue Creek to benefit approximately 118 properties that included 55 residential and 13 commercial structures. One of the key components of the master plan was resident coordination and building consensus to gain support for the project and easement agreements.

An alternative analysis was completed, which included extensive public outreach in the form of surveys, public meetings, and project website; inter-departmental coordination with City staff; Council meetings; and engineering analysis, including but not limited to feasibility, constructability, costs, and permittability of proposed improvements.

The City preferred an alternate that included a more holistic and strategic approach to opening the creek by buying out targeted properties for improving conveyance and floodplain storage; installing meanders, pools, riffles, and grade control structures; and planting native vegetation to improve water quality, floodplain function and habitat, aesthetics, and quality of life. This approach was also supportive of a sustainable strategy to address climate change (increased flows) and resiliency (reduced depth and duration of flooding and improved safety) for long-term community benefit.

The first phase was successfully completed and included over 2,800 linear feet of stream bank stabilization, 12 new meanders, and 12 grade control structures, as well as planting 4.6 acres of the riparian area with native vegetation. The construction of Phase I was completed on schedule and within budget.  Phase I was funded through Section 319 Grant funding, Green Infrastructure Grant Opportunity (GIGO), and Riverboat Funding. HR Green services included the preparation of 319 and GIGO grant applications, which resulted in grant funding totaling $2,622,967 with a local share of only $201,767 or just 8% of the total amount paid by the City. The project is permitted through various regulatory agencies including ACOE, IDNR-OWR, IEPA, IDNR, and KDSWCD. The project was also coordinated with FEMA for CLOMR approval.

Upon completion of Phase I, approximately 28 properties will benefit from the reduced floodplain. The proposed BMPs will help remove approximately 314 tons/year of sediments, 17,758 lbs a year of TSS, 287 lbs a year of phosphorous, and 715 lbs a year of nitrogen. Upon completion of all of the improvements proposed in the Master Plan, all of the 118 impacted properties will be removed from the 7^th Avenue Creek floodplain.

The 7th Avenue Creek project is overwhelmingly supported by the community. It is environmentally friendly and is a great example of a flood reduction and water quality project. While it will help satisfy the environmental needs of the watershed, it also enhances the quality of life with reduced flooding and improved resiliency and ultimately provides an attractive natural amenity the community can enjoy long-term.