Designing Innovative Natural Infrastructure to Protect Kenosha Dunes
Restoring Ecological Health and Aquatic Biodiversity (REHAB) in Southeastern Wisconsin’s Lake Michigan Coast
This project is facilitating innovative natural infrastructure approaches for Restoring Ecological Health and Aquatic Biodiversity (REHAB) of degraded dune and beach systems in southeastern Wisconsin. The primary focus is on the Kenosha Dunes complex at Chiwaukee Prairie State Natural Area, where rapid erosion is threatening this unique dune ecosystem. These nature-based design concepts could be applied to similar sites to enhance coastal community resilience and fish and wildlife habitat throughout Southeastern Wisconsin’s Lake Michigan coast.
Kenosha Dunes – A Rare Ecosystem
Kenosha Dunes is a rare Great Lakes dunes ecosystem located within the Chiwaukee Prairie State Natural Area along the Lake Michigan Shoreline in Kenosha County, Wisconsin. The site provides habitat or refuge for more than 400 species of vascular plants, including 26 rare, threatened or endangered species. Five of the most endangered natural community types of the Midwest are found within the State Natural Area. As a whole, the Chiwaukee Prairie State Natural Area is recognized as a Conservation Opportunity Area of global significance by the Wisconsin Wildlife Action Plan and a Wetland of International Importance by the Ramsar Convention. Kenosha Dunes is a popular recreation area where users can experience these unique ecosystems and Lake Michigan.
Coastal Erosion Issues
Kenosha Dunes has experienced severe erosion in recent years that has resulted in the loss of up to 25 feet per year of the dunes since 2014. While coastal erosion is an ongoing natural process, since 2014 a number of large storms have created extreme waves that, combined with above average water levels on the lake, have battered the shoreline. Kenosha Dunes was protected by a degraded revetment (see 2012 photo below) that has been significantly damaged by these storms and no longer provides protection to the coast. As a result, Kenosha Dunes has been eroding at a rate as high as 25 feet per year for the past 4 years (see 2018 photo below). With Lake Michigan water levels projected to remain above average for the foreseeable future, this rapid erosion is expected to continue without any intervention.
Slide to compare 2012 and 2018 erosion and water level conditions at Kenosha Dunes
Our webcam at the site has been capturing the ongoing erosion since October 2019. You can see a comparison of our first image with the most recent image below. All webcam images are accessible here.
Slide to compare October 17, 2019 and the most recent image at Kenosha Dunes
An Innovative Natural Infrastructure Approach to REHAB Kenosha Dunes
This project will design a system of submerged sills to protect the dunes from future erosion and improve coastal and marine habitats. The submerged sills will be a series of underwater structures that “trip” large waves before they reach the shore, which reduces the amount of wave energy that impacts the coast. This concept of “tripping” waves is how submerged features like reefs, shoals and bars naturally protect the shore and is used in other constructed approaches like submerged breakwaters and artificial reefs. The lower wave energy environment on the shoreward side of a sill offers a potential locations for marine habitat while the protected coast can support beach and dune habitat. This is in contrast to the existing rock revetment at the site, which eliminates beach habitat and creates a high energy nearshore due to wave reflection from the armor.
A unique challenge in tripping waves in the Great Lakes is that Lake Michigan water levels vary over a range of over six feet historically. The water depth above a submerged sill is an important criteria for how much it can reduce wave energy, so this water level fluctuation presents a challenge in tripping waves. This innovative submerged sill concept uses multiple “layers” of submerged sills at different elevations to be effective at reducing wave energy across different water levels. This project will analyze potential submerged sill layouts and elevations to find an optimal configuration to protect the dunes. From there, the sill structures will be designed to withstand the wave forces that Lake Michigan will subject them too.
Fish and Wildlife Habitat Connectivity
The submerged sills will be designed to also provide habitat benefits to the site. The submerged sill design will replace the relic revetment, which served as a barrier between the dunes and the lake. The offshore submerged sills will promote enhanced habitat connectivity between the upland, nearshore, and offshore environments. Fish habitat will be designed into the submerged sills using a variety of approaches which may include incorporating a gradation of rock sizes or artificial reef structures to provide fish refuge and spawning locations. The reduced wave energy environment behind the sills may support the growth of submerged aquatic vegetation which cannot establish on the current open coast, which can further enhance fish habitat. Upland restoration and plantings will rehabilitate valuable dune habitat that has been lost due to revetment construction and the ongoing erosion.
The project will also identify nearby beaches where a similar approach may be a suitable method to manage shoreline erosion while providing habitat connectivity benefits.
Natural Resources Foundation of Wisconsin
Wisconsin Department of Natural Resources
University of Wisconsin-Madison Civil and Environmental Engineering Coastal Sustainability Lab
University of Wisconsin Sea Grant Institute
University of Wisconsin-Milwaukee School of Freshwater Sciences
Wisconsin Coastal Management Program
RED BARN Design and Engineering, S.C.
Geo-Professional Consultants, LLC
The Nature Conservancy
United States Army Corps of Engineers
United States Environmental Protection Agency
This project is made possible due to support from:
The Fund for Lake Michigan
National Fish and Wildlife Foundation – National Coastal Resilience Fund