Sediment Reduction Through Coastal Wetland Construction
North Chicago in Lake Co. on Lake Michigan,
Foss Park District
Basin Program Funds:
Urbanization along the shores of the Great Lakes has led to increased levels of nonpoint source pollutants and sediments flowing into the lakes through surface runoff. This is evidenced by extensive plumes of sediment entering Lake Michigan through washouts across beaches or directly into the lake immediately following heavy rainfall events. Washouts are seen at the base of both vegetated and actively eroding sections of Illinois coastal bluffs.
It is common knowledge that plants can be useful for stabilizing eroding banks of lakes and streams. Also plants are known for their ability to uptake nutrients and act as natural filters for some pollutants. It is known, but not well documented, that coastal dune and swale wetlands also function well as natural filters.
Foss Park District, City of North Chicago, Illinois is planning to develop a 1,500-foot reach of Lake Michigan shoreline at Foss Park. The existing shoreline at the north end of the park has an actively eroding bluff. To the south, is a bluff fill in the process of being restored. There is also an existing dune field with associated wetland that is deteriorating due to excessive runoff and siltation from the fill. The beach and the park are in poor condition and have experienced minimal usage. The overall effect is that Foss Park does not take full advantage of Lake Michigan as a recreational resource nor attract visitors to the park and the City of North Chicago. A multi-faceted project is planned to enhance the bluffs, restore and expand the wetlands, and enlarge and protect the beach. Our intent is to make this coastal resource more useful to the community, enhance the dune/swale ecology and at the same time improve the beach/wetland’s ability to filter runoff.
The intent of this demonstration project is to test methods for reducing sedimentation and filtering urban runoff by construction of a dune and swale wetland system at the base of a partially eroding Lake Michigan bluff. The site is approximately 1,600 feet of lake frontage. The site will be mapped for topography, erosion severity, beach and dune development and existing vegetative growth. A stone-lined swale will be constructed. An overflow system will be constructed in the wetland system. Monitoring will be performed.
The plan includes expansion and improvement of the south wetland and construction of a stone-lined swale along the toe of the coastal bluff to the north. The purpose of the swale is to divert bluff runoff into the wetland. After a site survey and consultation with our technical advisors we’ve decided not to use stone to line the swale but rather native clay. In addition, the swale would be planted with wetland species to expand the filtering capability of the entire system.
A project team was assembled consisting of students from Northeastern Illinois University and Northwestern University. A preliminary plan was developed in the summer, 2001. Methods, materials and procedures were then inputted into the design by the team, surveys of the bluff, dunes, beach, and near-shore bathymetry were conducted in September, 2001, and an inventory of existing plants and soils was completed in the fall, 2001. A design for wetland restoration and development was approved by the park district and reviewed by the team professionals. The plan involves installing a dormant native wetland plant seed mix that was formulated based on an inventory of natural dune/swale systems at Illinois Beach State Park. The seed mix was planted January 9th, 2002 in the south wetland area and north swale. A silt fence was installed at the toe of the south bluff restoration area to reduce siltation into the project area. Monitoring of wetland plant development was initiated in spring, 2002. Installation of sediment traps was completed on July 8, 2002.
The existing wetland area was expanded to include the swale and both were planted with native wetland species. Although a large percent of the newly installed wetland plants appear to have survived (as of July, 2002), they have not developed to the extent that they can be identified due to a very dry growing season.
Removal (by others) of non-native shrubs and trees in the wetland area is planned but has not yet been accomplished. Silt and clay continue to flow from the adjacent bluff. The silt fence has trapped approximately 0.1 m3 (per linear meter of bluff) of silt and clay that otherwise would have entered the system. Until the adjacent bluff can be stabilized and revegetated, silt will continue to impact the system. When the bluff is stabilized and revegetated, we will remove the silt fence. Monitoring of sediment traps will begin on July 15, 2002 and continue through 2003. Monitoring of the wetland plants will also continue through 2003.
The biggest problem encountered was the incomplete revegetation of the bluffs adjacent to the wetland project area. This work was to be completed by others prior to initiation of the project. Silt and clay were actively entering the wetland area. To mitigate this problem, we requested that silt fence be installed. An unexpected benefit was the measurement of sediment trapped by the silt fence over the winter and spring 2002. However, although eroded bluff sediment is not transported into Lake Michigan, we do not expect the system to be fully functional until the bluff is stabilized.
After the installation and monitoring are complete, periodic attention will be necessary for proper management of the dune/swale wetlands. We plan to involve a community-based environmental group in the continued stewardship of this valuable resource.
Plans for expansion and protection of the beach with a series of near shore stone breakwaters and revetment have been approved by the Foss Park District. This will allow for safer access to the lake and assure that Lake Michigan storm waves will no longer erode the beach and coastal bluffs. The most vulnerable part of Foss Park is the narrow beach and bluff at the northern-most end of the park. Approximately 300 metric tons of clay, soil and organic debris are washed into Lake Michigan annually. This problem, although unusual in Illinois, is common in other Great Lakes states like Wisconsin. To mitigate the problem, we propose to construct a series of near shore stone breakwaters and a stone revetment with a perched wetland swale. The swale will to tie into the south wetlands. Combined with bluff planting utilizing native species, it will help prevent further wave attack and divert non-point-source pollutants to the newly constructed dune and swale wetland system at the south end of the park. We are seeking funding from the State of Illinois for this work.
Contact: Charles Shabica, 773-442-6054