WATERWAY AND LOCATION: The project would affect waters of the United States associated with Prairie Creek. The project/review area is located on an approximately 77.63 acre parcel along Prairie Creek located in Section 8, Township 21 North, Range 1 East; at Latitude 40.29265 and Longitude -89.11302; in McLean, McLean County, Illinois.
EXISTING CONDITIONS: The site is primarily undeveloped land along Prairie Creek, surrounded by agricultural fields that have been in production since before 1940. Prairie Creek has been straightened in sections between 1967 and 1998. East 50th Road North crosses the site with a bridge over the creek.
PROJECT PURPOSE/BANK OBJECTIVES: The fundamental objective of compensatory mitigation is to offset environmental losses resulting from unavoidable impacts to waters of the United States (WOTUS), as authorized by Department of the Army permits. Other objectives include: enhancing and creating wildlife habitat; re-meandering straightened creek channel to increase sinuosity; constructing floodplain benches to slow water flow and increase flood storage capacity; stabilizing streambanks with native vegetation; restoring native vegetation within the riparian buffer; and selling mitigation credits for project impacts proposed by other entities.
PROJECT DESCRIPTION/BANK ESTABLISHMENT: The bank sponsor proposes to complete activities on approximately 77.63 acres along Prairie Creek. The project would result in the generation of stream compensatory mitigation credits. The goal of the project is to restore 5,681 linear feet of stream with buffers to generate an initial estimate of 71,864.65 stream credits.
The proposed project encompasses restoration along two reaches of Prairie Creek, separated by East 50th North Road, totaling 4,511 existing feet which will be increased to 5,681 feet post-restoration, an overall increase of 1,170 linear feet. The formerly channelized creek will be re-aligned to increase sinuosity from an existing 1.07 to 1.35. Alongside re-meandering, the project incorporates the construction of 16-foot wide floodplain benches (8 feet on each side of the stream) adjacent to the channel. These benches will lower the floodplain elevation, reduce entrenchment, and provide flood storage and bank stabilization by reducing shear stress during high flow events.
Cross vanes will be installed at intervals approximately seven times the bankfull width. These structures will direct flow towards the center of the channel, reducing streambank erosion and creating pool-riffle sequences. Bank reshaping and re-sloping will address existing erosion, particularly near the roadway bridge and where the re-meandered channel connects to the existing alignment. Streambanks will then be seeded with a Wetland Seed Mix to promote vegetative stabilization. Additionally, the project will address non-point source pollution by daylighting subsurface drainage tiles that currently discharge directly into Prairie Creek. These tiles will be redirected through splash basins and vegetated swales, allowing for nutrient filtration and reducing the influx of nitrogen and phosphorus into the stream.
In addition to the in-stream work, a 300-foot wide riparian buffer will be reestablished on both sides of the creek. This will involve the removal of invasive and undesirable species followed by seeding with the NRCS Stream Buffer Mix or a comparable alternative.
SERVICE AREA: The proposed mitigation bank will be in the South Service Area.
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