Lake Michigan coastal erosion and bluff failures

January 30, 2011

By Carolyn Rumery Betz

In 2008, heavy rain triggered mudslides in Grant Park—with trees and chunks of land literally skidding down bluffs, across the beach, and into the lake—a sober reminder that coastal erosion poses a real threat along Lake Michigan.

Concordia University in Mequon knows all too well how important it is to protect against bluff failure. For more than 20 years, the 130-foot-high bluff that stood between the campus and the lake eroded about a foot per year. It took eight years to plan, design, and execute a bluff stabilization project to prevent more valuable property from tumbling into Lake Michigan.

The $10 million project, completed in 2007, “de-watered” a 2,800-foot-long section of bluff by building in drains to collect water and thus reduce saturated soil pressure. Contractors re-graded the slope, built a series of switchbacks down to the beach, created an artificial wetland, and added shoreline revetments to protect the base of the bluff from wave action. What was once a liability is now an attractive amenity providing students with safer access to the lake.

Not every shoreline property owner along Lake Michigan has the means to reconstruct their land as dramatically as Concordia—and even their reengineered bluff continues to erode—but each shares a common challenge in coastal erosion.

mudslides 021

Mudslides defaced the bluffs of Grant Park after heavy rains in June 2008. ~photo Michael Timm

There are two major types: shoreline erosion and coastal bluff failures due to instability. Both types of erosion can lead to loss of property, dwellings, and personal injury, but bluff erosion is particularly problematic on the western shore of Lake Michigan.

“Most of Lake Michigan bluffs are marginally stable at best,” said Gene Clark, a coastal engineer with the University of Wisconsin Sea Grant Institute. “Some are still responding to high water of the 1980s, eroding at the bottom.” The mixture of sandy and clay soils, rain, melting snow and groundwater flow, and the freezing and thawing cycles of ice during the winter months create instability. Bluff erosion may happen abruptly with landowners losing as much as 50 feet of their backyard in a single landslide, as happened in one weekend storm in 1985.

In the tug-of-war between the force of gravity on soil masses and the resistance against it, gravity will always win, pulling a slope to a new equilibrium. The resistance occurs between tiny soil particles or along large soil surfaces called potential failure planes. When the particles or planes can no longer resist because of inflow of water or freezing or thawing of ice, they give way. The particle-scale movement may not be noticed, but movement along planes is what causes landslides, such as what occurred at Grant Park in 2008.

“It’s like a teeter-totter where it doesn’t take much to turn from stable to unstable,” Clark explained. “All it takes is a severe storm, someone watering, someone cutting vegetation that was providing some stability, someone putting dead vegetation on the bluff front face—it just makes it worse.”

Controlling Coastal Erosion

Property owners should get the advice of a coastal engineer or professional landscape architect to help stabilize coastal shorelines and bluffs, according to Clark, because not every beneficial approach is intuitive. Planting vegetation can stabilize the shore or the front of the bluff, but it can sometimes backfire. Planting grass or sod requires watering, and adding water may activate soil movement.

Bushes, on the other hand, have a deeper root structure, Clark said. Dogwoods and willows can add greater stability because they send out suckers and put down more roots when pruned.

Clark said stability is not acquired by adding things like old Christmas trees, dead leaves, or tree branches to the bluff face or an eroding path. These objects can actually make things worse by blocking sunlight from promoting natural live vegetation, channelizing flow around the objects when it does rain, or allowing water to pool or pond instead of infiltrating into the ground.

Since Mother Nature will always win in the end, coastal experts recommend placing structures far from the shoreline. Clark warns that even septic systems, especially mound systems, should also be sited far from the shore. Mound septic systems are continually dosing the ground with water, which can make the ground and bluff unstable and prone to erosion.

concordia 1956-2000A

From 1956 to 2000, the Concordia University bluff top (red zone) receded 14 feet and the bluff toe (blue zone) receded 106 feet. The bluff angle also got steeper, from 17 degrees to 24 degrees. ~image courtesy UW Sea Grant

(See geography.wisc.edu/coastal for the 3D animation of over 40 years of Concordia bluff erosion.)concordia 1956-2000B
Most coastal communities use shoreline zoning as a proactive development tool, according to David Hart, a geographic information specialist at the University of Wisconsin. Hart is developing an electronic toolbox full of aids to be used by coastal managers, including historical databases showing erosion over time (site in development at wicoastalatlas.net). “If people are fighting setback limits, you can show them how the shoreline has changed over time,” said Kate Barrett with Wisconsin DNR’s Office of the Great Lakes. “The regulations are in place to protect people and their property.”

The delineation of building setbacks is traditionally based on the location of the Ordinary High Water Mark (OHWM), the place where the regular action of water against the bank leaves a distinct mark. That may not be easily seen, particularly on the Great Lakes. Currently, Lake Michigan is at a prolonged low, making the OHWM seem extremely far from the shore, tempting placement of dwellings much closer to the shoreline than would be allowed during a high-water period.

Effects of Climate Change

The Wisconsin Initiative on Climate Change Impacts predicts that increased storm events, with more precipitation, increased wind velocities, reduced ice cover, and increased nearshore wave height will occur as part of our changing climate. Dramatic events like the 2008 Grant Park mudslides are sure to continue, so coastal experts say we must be proactive in setting back our dwellings to accommodate coastal erosion, not only on the bluffs, but on the shoreline as well.

Carolyn Rumery Betz is a science writer for the University of Wisconsin Sea Grant Institute, which supports research, education, and outreach dedicated to the stewardship and sustainable use of the nation’s Great Lakes and ocean resources (seagrant.wisc.edu).

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Comments

4 Comments on "Lake Michigan coastal erosion and bluff failures"

  1. Tweets that mention Lake Michigan coastal erosion and bluff failures : The Bay View Compass -- Topsy.com on Tue, 1st Feb 2011 8:18 am 

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  2. Bluff collapse at We Energies power plant in Oak Creek : The Bay View Compass on Mon, 31st Oct 2011 6:23 pm 

    […] our story about Lake Michigan bluff erosion and failure here. Share this:PrintEmailFacebookDigg Copyright 2011 by Bay View Compass. All rights reserved. […]

  3. BRIAN W HAWKS NILES MI on Wed, 18th Dec 2013 5:34 pm 

    SINCE THE RAIN,WIND,AND SNOW ARE THE MAIN CAUSE OF EROSION,WHY CANT ONE PUT A “FENCE OF WOOD CHIPS ” AGAINST THE FACE OF THE CLIFF? STEEL POST 3 FEET APART ANCHORED INTO THE CLIFF BASE WHERE POSSIBLE AND MESHED WIRE TO CONTAIN THE CHIPS .STARTING OF COURSE AT THE TOP OF THE CLIFF AND WORKING YOUR WAY DOWN THE CLIFF IN TIERS .THIS IS AN INSULATION FROM THE ELEMENTS METHOD THAT I THINK HAS POTENTIAL ,VERY SIMPLE,EASY TO INSTALL, LIGHTWEIGHT , AND CHEAP MATERIALS USED.MY FATHER INVENTED BEACH SANDING FOR INLAND LAKES IN THE 1960 AND I WORKED WITH HIM FOR MANY YEARS.GOOGLE BEACH SANDING MICHIGAN .THANK YOU ,BRIAN HAWKS

  4. Erosion | Failure Mechanisms on Mon, 3rd Feb 2014 12:50 pm 

    […] can pose major problems to structures built on hill sides [b], in coastal areas, and near water ways [c].  As the soil on which a foundation is built is eroded […]

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