4 minute read
Lake County Ravine 8
Highland Park, Illinois, United States
Stabilizing a stream’s hydrology and restoring habitat. The Ravine 8 project area is about two hectares, primarily consisting of one ravine with an ephemeral stream and smaller areas of Lake Michigan bluff and foredunes. Because of urbanization and storm events, the ravines along the north shore of Lake Michigan have been used as conduits for both open-channel stormwater and piped sanitary sewers, causing erosion and loss of habitat. The City of Highland Park and the U.S. Army Corps of Engineers (USACE)–Chicago District partnered under the Great Lakes Fishery and Ecosystem Restoration program to restore the ecological integrity of Ravine 8 while considering the preservation of critical infrastructure. At the project’s outset, the City replaced the broken sanitary sewer and separated the stormwater to discharge into the ravine. The partnered Section 506 project then used Engineering With Nature (EWN) features within the stream channel by installing robust step-pools of glacial and river stone in steep sections and seeded a sediment (coarse sand and pea gravel) source for the new stream to transport during floods. Coupled with native plant restoration, this EWN methodology ensured channel stability for continued human uses while providing native ephemeral stream and riparian woodland habitats. Removal of a small dam and invasive plant species eradication were also included. The project was completed in 2019.
Article Cover: Sand stream and native vegetation restored with a sanitary sewer underneath. Native plant communities will continue to establish, becoming more active in stabilizing the ravine stream and woodland habitats. (Photo by Robbie Sliwinski, USACE Chicago District)
Producing Efficiencies
The project used the most up-to-date science of what riverine ecosystems and species require, coupled with hydraulic engineering to ensure continuation of human use and existing infrastructure. Periodically, about every three to five years, placing a relatively small amount (almost four cubic meters) of coarse sand and small gravel at the head of the ravine ensures sediment transport is satiated to prevent erosion of the downstream ravine banks. This also provides the ravine stream bottom with coarse substrate to help with stability. Clearing out weed trees and shrubs also opened the canopy of the degraded woodland, which allowed for a native understory to establish to further stabilize ravine slopes and banks.
Using Natural Processes
An important part of riverine habitat restoration includes considering sediment input and transport. Sediment primarily enters a river channel via surface erosion. Because of urbanization, there is no longer surface erosion in the Ravine 8 watershed. Surface erosion of the banks and ravine slopes is part of the natural channel evolutionary process, in which a geologically mature ravine with perennial stream would form. This is a positive source of river sedimentation, providing the right amount and types of substrate input typically transported as bedload to form the basis of benthic habitat, substrates, and channel features. Because ravine slopes cannot be allowed to naturally erode, threatening bordering homes, a sediment transport source has ameliorated erosion to date.
Broadening Benefits
This project has provided social, environmental, and economic benefits to the residents that live along the ravine. Social benefits include an awareness of who is living on the ravine and how certain individual actions along the ravine affect everyone. Economic benefits include prolonged protection of critical infrastructure, properties, and homes. Values of a land parcel typically increase with beautified nature and ensured stability to home structures. Ecosystem benefits provided by this project include ravine dynamics, stream geomorphology and habitat, native plant communities, invasive species eradication, connectivity, restoration of sloped wetland communities, and increased native species richness and abundance.
Promoting Collaboration
To accomplish this cost-shared project, temporary easements from over 10 landowners were acquired by the nonfederal sponsor, the City of Highland Park. The city diligently worked to focus the interest of the land- and homeowners along the ravine to foster a consensus that the federally led restoration project was the right action for the ravine ecosystem and the people who live along it. The nonfederal sponsor will continue postconstruction monitoring through 2025.
