Appeared in the Gazette, Fall/Winter 2019
By Charles W. Shabica, Ph.D., P.G.
Educated at Brown, Yale, and the University of Chicago, Charles Shabica is President of Shabica & Associates, Inc., Coastal Scientists and Engineers, and is Emeritus Professor of Earth Science, Northeastern Illinois University.
High lake levels and more intense storms have many Great Lakes coastal communities in a state of uncertainty over how to mitigate property damage, flooding, and beach loss. While it is unlikely that humans can stop or slow global warming, there is growing evidence that in many regions, human intervention can help adapt to climate change and associated intense storms.
Shore erosion and flooding on Great Lakes coasts, as well as our maritime coasts, are a function of water level, storm intensity, nearshore water depths, land elevation and geology, and shore protection systems. For the last 12,000 years, the earth has been in an interglacial warming period where sea level has been slowly rising; accelerated by human production of greenhouse gasses and burning of forests that absorb carbon dioxide. While the ocean may rise 3 to 6 feet by 2100 due to climate warming, Lake Michigan levels rose 6 feet between 2013 and 2019, a bellwether for sea level rise on our ocean coasts. The good news: Coastal scientists and engineers have learned from nature’s shore protection that with proper planning and system maintenance, it is possible to cope with an evolving dynamic coast of eroding bluffs and beaches, using sustainable methods to mitigate erosion problems exacerbated by high water levels. Great Lakes examples include the Chicago Lakefill, sand nourishment at Illinois Beach State Park and rocky breakwaters (islands) on the Illinois North Shore.
City of Chicago Lakefill: More than 100 years ago, the Chicago Plan was developed to cope with climate uncertainty and lake storms. The plan was simple and elegant and today is a model for coastal cities around the globe. There are two elements to the plan: raise the elevaton of the city with fill (originally built on sandy marshland) and protect it with elevated parkland built on lakefill. Called the Burnham Plan, with an upgrade in 1988, it continues to function well. Chicago’s Step Revetments and bay beaches provide a safe shore as well as user-friendly access to Lake Michigan. An important component of the plan, nearshore barrier islands (breakwaters) was implemented in only one location, Northerly Island (Once Meigs field, now parkland thanks to Mayor Richard M. Daley).
Illinois Beach State Park Sand Nourishment: With narrowing beaches in many locations, humans have stepped in and bolstered beaches with sand transported from downdrift sand traps or inland or offshore sources. It’s a way of mimicking nature, and we’ve had good success with it in many areas especially the Atlantic coast where scientists have documented that regular beach nourishment can reverse shore erosion. Records showed a mean rate of shore erosion of 22 inches per year prior to 1960 and a mean rate of shoreline accretion of 2 inches per year from 1960 to 2007 despite accelerating sea level rise.
There is one location in Illinois where regular beach nourishment can be a success, Illinois Beach State Park. It is one of the most dynamic beach cells on the western shore of Lake Michigan, and has serious erosion problems that can be ameliorated with simple sand management. The south end of the park is gaining sand at the expense of beach erosion to the north, where one storm claimed 150 feet of lakeshore. Sand backpassed from Waukegan Harbor up to the north end of the beach was proposed by the State Coastal Geologist Dr. Michael Chrzastowski years ago, but sadly it has not yet happened despite abundant evidence for its success.
North Shore Breakwaters: North Shore communities to the south face a bigger problem: sand loss exacerbated by lakebed clay downcutting (similar consequence as sea level rise: deeper water at the shore and bigger and more destructive waves). We have learned that natural coastal barrier islands, whether sandy or rocky, have protected our coasts for millennia. On the North Shore, beach nourishment needs to be supplemented with construction of nearshore breakwaters (that mimic barrier islands) or the sand will be lost to deep water (as reported by the U.S. Army Corps of Engineers years ago). This solution was sucessfully applied to the Lake Forest and Lake Bluff public beaches in the late 1980s. Today many private as well as public beaches on the North Shore are protected with similar structures, affectionately called “pocket beaches.” They are designed to accommodate extreme changes in water levels and lakebed downcutting and have sucessfully stood the test of time.
In summary, with proper planning and resources it is possible to cope with a warming climate with sustainable coastal solutions that include lake fills, sand management, and construction of barrier island breakwaters.
Ezer, T., and Atkinson, 2014, Accelerated flooding along the U.S. East Coast: On the impact of sea-level rise, tides, storms, the Gulf Stream, and the North Atlantic Oscillations. Earth’s Future, 2(8), pp 362-382. https://doi.org/10.1002/2014EF000252
Learn, Joshua, January 31, 2019, Beach building is keeping the Atlantic Coast from going under. They discussed Armstrong and Lazarus (2019) who analyzed U.S. Geological Survey records from 1830 to 2007 along more than 2,500 kilometers of Atlantic Coast shoreline, from Massachusetts to South Florida.
American Geophysical Union American Geophysical Union
Read more at: https://phys.org/news/2019-01-beach-atlantic-coast.html#jCp
Shabica, C.W. et al, 1988, Shore Management Recommendations for Martha’s Vineyard, Massachusetts – South Beach, East Chop and Sengekontacket Pond. Report to the Martha’s Vineyard Commission.
Beaches composed of sand, gravel and cobbles are products of land erosion transported to the shore by gravity, rivers, wind, waves and along shore currents. A wide robust beach with a continuous sand supply will provide protection of the upland from storm waves and rising lake/sea level. If the sand supply is cut-off by dams, harbors or shore protection with seawalls or revetments, the system becomes sediment-starved and vulnerable to catastrophic storm damage.