State of the Beach/State Reports/IL/Beach Erosion
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The Illinois coast of Lake Michigan is a dynamic setting influenced by waves, ice and changing lake levels. The potential for coastal erosion exists along nearly the entire Illinois coast.
Two aspects of coastal erosion along the Illinois coast are important as a framework for understanding past, present and future erosional trends.
Coastal Erosion in the Natural Setting
Prior to any human modifications, the natural setting along the Illinois coast was nearly all erosional. There was an abundant supply of littoral sand moving along the shore. However, this sand was in transport to a depositional zone along the central Indiana coast. The exception to the erosional trends was the southern part of the Zion beach-ridge plain from near the mouth of Dead River southward to the North Chicago shoreline. This was the state’s only accretional shore. The accretion resulted from the southward translation of the beach-ridge plain.
Lake Level Influence on Coastal Erosion
Erosion along the Illinois coast gains considerable public and media attention during times of high lake levels. High water causes partial to total submergence of some beaches, storm waves can damage and overtop shore structures, and localized coastal flooding may occur. A common misconception is that coastal erosion is limited to times of high lake levels. The reality is that erosion can be an ongoing process regardless of lake level. Changing lake level simply shifts the erosion zone either landward or lakeward.
Four Categories of Illinois Coastal Erosion
Four categories of coastal erosion have been and continue to be an issue along the Illinois Lake Michigan coast and the inland waterways. These correspond to different locations on the topographic/bathymetric profile:
Shore erosion refers to the erosion of the exposed beach or land area adjacent to the shoreline. Shore erosion results in a landward translation of the shoreline as well as loss of beach area and loss of beach sand volume. A related process to shore erosion is the damage and deterioration of engineered structures that occur along the shore such as revetments, riprap, groins, bulkheads and breakwaters. Because of the important role of shore-protection structures along the Illinois coast to stabilize the land/water interface, damage and deterioration of these structures can be equally important as any erosional loss of beach area or land area.
The natural setting along the Illinois bluff coast was one of nearly continuous bluff erosion. The bluff erosion commonly involved wave erosion cutting into the toe of the bluff and undermining the bluff slope. The bluffs could also erode due to the influence of either surface runoff or ground water respectively moving over or through the bluff materials. The late 1970s to 1990s saw substantial shore protection installed to halt bluff erosion. By 2000, a survey of the bluff coast determined that wave-induced bluff erosion was active along no more than about 600 feet of the entire bluff coast.
The term lakebed erosion refers to underwater erosion across the bed of the lake. This erosion does not refer to the sand or gravelly sand that may occur along the lake bottom. Lakebed erosion refers to the erosion across the cohesive layers of glacial till or clay that underlie the sand. This type of erosion is also referred to as lakebed downcutting, or simply downcutting. The cause is wave and current action as well as ice. Lakebed erosion is non-reversible erosion because the loss of the cohesive material cannot be replaced other than by a new glacial episode. The long-term impact of lakebed erosion is the lowering of the lake-bottom profile. As a result, deeper water occurs closer to shore and the profile is steeper between the beach and nearshore. The deeper water and steeper profile allows larger waves to impact the shore, which can increase the potential for erosion along the beaches and along the toe of the bluffs.
Waterway Bank Erosion
The banks along the inland waterways are subject to erosion by undermining and slope instability. Bank erosion can be from natural processes or human activity such a boat wakes.
Erosion Information Reports and Websites
Shoreline Erosion Issue Paper from the Illinois Coastal Management Program.
United States Great Lakes Shoreline Recession Rate Data Final Report (1994) by the U.S. Army Corps of Engineers provides some historical (1872 to 1975) erosion (recession rate) data for Illinois' Lake Michigan shoreline. The report also states:
The Illinois State Geological Survey has also been active in examining shoreline recession having produced reports dealing with coastal geology and coastal zone management (Illinois State Geological Survey, 1977) and an atlas of the Illinois shore highlighting shore features, damaged areas and shore protection structures (Illinois State Geological Survey, 1988). In addition, they have conducted surveys for 28 profiles offshore of Chicago's Lincoln Park taken in 1976 and again in 1987 (reported in Nairn, 1992), and for 20 profiles at North Point Marina near the Illinois/Wisconsin state line taken annually between 1988 and 1991 (Chrzastowski and Riggs, 1989). Shabica et al (1991) also present profile surveys for several sites between Fort Sheridan and Evanston documenting the loss of sand cover between 1975 and 1989.
Finally, a number of other smaller scale erosion related studies taking place along the Illinois shoreline have been summarized by Folger et al (1990) in the proceedings of the 2nd Southern Lake Michigan Coastal Erosion Study Workshop.
The Heinz Center's Evaluation of Erosion Hazards (April 2000) states:
The Great Lakes coasts extend for 3,600 mi (Federal Emergency Management Agency, 1989), and are composed of a variety of shore types, ranging from high rock bluffs to low plains and wetlands. Coastal erosion in the Great Lakes is affected by many factors, including cyclically changing lake levels, disruption of longshore transport of beach building material, and storms. Rates of bluff and dune erosion along the shores of the Great Lakes vary from near zero to tens of feet per year because of annual variability in wave climate and lake levels (National Research Council, 1990). The Great Lakes have experienced a series of high lake levels in the past two decades, with the highest peak occurring in 1987 (U.S. Army Corps of Engineers Detroit District, 1997). High lake levels increase bluff recession rates by increasing wave attack on the base of the bluff.
In many areas of the Great Lakes, bluff erosion produces beach-building sediments. However, both tributary and shoreland sources of sediment are depleted by navigational improvements and dredged material disposal practices, which remove these sediments from the littoral system. Ice ridges that form and break up each winter along the shoreline also cause erosion by trapping sand in floating fragments of ice that are carried offshore into deep water. This continuing natural process is one of the principal mechanisms by which sand is lost from the nearshore system (U.S. Geological Survey, 1992). The hardening of the lakeshore with erosion control structures can also reduce sediment supply and adversely affect natural processes.
A source of information on coastal erosion in Illinois (southern Lake Michigan) is the USGS Fact Sheet Coastal Erosion of Southern Lake Michigan.
Another resource with links to many publications on coastal geology and erosion in Illinois is the Website of the Illinois State Geological Survey.
A reference document is a 1994 edition of the Journal of Great Lakes Research (1994, vol. 20, no. 1). It includes a special section on Illinois (and Indiana) coastal erosion and is a summary of a major multi-year study. Abstracts of several of the articles in this issue can be viewed here.
Substantial information regarding soil erosion and sedimentation in the Great Lakes Region can be found at the Website of Great Lakes Information Network.
Also try the Website of the Illinois Natural Resources Conservation Service
Some area-specific coastal erosion data and information is as follows:
- North Point Marina is built along a shoreline that has the most severe erosion recorded along the Illinois coast. Shoreline recession has occurred at a long-term average rate of about 10 feet (3 m) per year.
- Contrasting with the net erosion at the north end of the Zion beach-ridge plain near North Point Marina is the net accretion near the south end of the sand plain in the vicinity of Waukegan Harbor.
In May 2017 the Chicago Tribune reported on the results of studies by Illinois Department of Natural Resources and the US Army Corps of Engineers. At Illinois Beach State Park, from 1939 to 2014, the shoreline retreated more than 600 feet, an average of 8 feet per year. In a little more than two years, from 2014 to 2016, erosion accelerated dramatically, with the loss of 184 feet of beach, an average of 84 feet a year. Farther south, in Waukegan, there's been an emergence of dune land over time. Since 1939, the breakwater featured on the city's seal has trapped enough sand to push the suburb's waterfront 860 feet into the lake, growing at a rate of 11 feet each year. Waukegan's North Beach Park collects 43,000 cubic yards of sand a year thanks to the city's breakwater. But as North Beach Park grows, the municipal beach that the breakwater was meant to protect has shrunk considerably. The city's longstanding commercial shipping industry has been crippled because sand perennially clogs its harbor.
General Erosion Data Resources
The Heinz Center's Evaluation of Erosion Hazards, conducted for the Federal Emergency Management Agency (FEMA), studied the causes of coastal erosion hazards and proposed a variety of national and regional responses. The study, published in April 2000, concentrates on the economic impacts of erosion response policies as well as the cost of erosion itself to homeowners, businesses, and governmental entities.
A NOAA website that has graphs of sea level data for many coastal locations around the country over the last 40 to 50 years and projections into the future is Sea Levels Online.
NOAA Shoreline Website is a comprehensive guide to national shoreline data and terms and is the first site to allow vector shoreline data from NOAA and other federal agencies to be conveniently accessed and compared in one place. Supporting context is also included via frequently asked questions, common uses of shoreline data, shoreline terms, and references. Many NOAA branches and offices have a stake in developing shoreline data, but this is the first-ever NOAA Website to provide access to all NOAA shorelines, plus data from other federal agencies. The site is a culmination of efforts of NOAA and several offices within NOS (including NOAA’s Coastal Services Center, National Geodetic Survey, Office of Coast Survey, Special Projects Office, and Office of Ocean and Coastal Resource Management) and other federal agencies to provide coastal resource managers with accurate and useful shoreline data.
A related site launched in 2008 is NOAA Coastal Services Center's Digital Coast, which can be used to address timely coastal issues, including land use, coastal conservation, hazards, marine spatial planning, and climate change. One of the goals behind the creation of the Digital Coast was to unify groups that might not otherwise work together. This partnership network is building not only a website, but also a strong collaboration of coastal professionals intent on addressing coastal resource management needs. Website content is provided by numerous organizations, but all must meet the site’s quality and applicability standards. More recently, NOAA Coastal Services Center has developed a Sea Level Rise and Coastal Flooding Impacts Viewer as part of its Digital Coast website. Being able to visualize potential impacts from sea level rise is a powerful teaching and planning tool, and the Sea Level Rise Viewer brings this capability to coastal communities. A slider bar is used to show how various levels of sea level rise will impact coastal communities. Completed areas include Mississippi, Alabama, Texas, Florida, and Georgia, with additional coastal counties to be added in the near future. Visuals and the accompanying data and information cover sea level rise inundation, uncertainty, flood frequency, marsh impacts, and socioeconomics.
Erosion Contact Info
Michael J. Chrzastowski
ICMP Coastal Resource Coordinator
Senior Coastal Geologist
IDNR, Illinois State Geological Survey
Hazard Avoidance Policies/Erosion Response
See the Erosion Response section.
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