Our Coastal Engineering Specialist Philip Keillor Answers
Twenty Frequently Asked Questions
about Great Lakes Water Levels and
Coastal Erosion
General Lake Levels Questions
Shore Erosion and Coastal Flooding Questions
Shore Protection Questions
Sources of Additional Information
Shore Erosion and Coastal Flooding Questions
Sources of Additional Information on Great Lakes Water Levels and Erosion
Shoreline erosion destroys house near Ogden Dunes, Indiana
(Michigan Sea Grant photo by C. Swinehart, April
1986)
Why should I care about high lake levels?
Because the millions of people living around the Great Lakes depend on vulnerable lakeside and harbor facilities for drinking water, electrical power, sewage treatment, and energy and manufacturing supplies, among many other services vital to lakeshore and inland residents alike. Many people also work in industrial and commercial facilities located on low-lying coastal areas, the operation of which can be impaired or shut down when lake levels exceed the water levels for which they were designed. High lake levels increase storm wave run-up and accelerate coastal erosion, occasionally causing lakeshore homes to be flooded or fall into the lake. Beaches and marina docks may become partly or completely submerged as well.
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What causes major changes in lake levels?
Primarily two factors: a prolonged period of heavy precipitation and little evaporation. Generally, lake levels are lowest in winter, when most of the region's precipitation is frozen in place in ice and snow cover, and evaporation increases as dry winter air masses pass over the lakes. Levels are highest in summer following the spring runoff of melting snow and ice.
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What are the ranges of lake level changes?
This century, the differences between the record high and low monthly mean lake levels were: Superior 3.8 feet (1.2 meters); Michigan and Huron 6.2 feet (1.9 meters); Erie 6.0 feet (1.8 meters); and Ontario 6.5 feet (2.0 meters).
Short-term water level changes are more dramatic and can last minutes or hours. Passing weather systems and wind shifts cause fluctuations in lake level, called seiches, which can raise lake levels from 6 inches to more that 1 foot for several minutes. Storm surges can temporarily raise lake levels several feet on the open coast and 5 feet in bays, for a few hours. At the eastern end of Lake Erie storm surges up to 8 feet have been recorded, along with a similar drop in water level at the opposite end of the lake.
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What difference can a change of 1 or 2 feet make?
A change of 1 foot is a normal seasonal range from peak summer levels to the low winter levels. Occasional changes in water levels — up to six or seven times the seasonal variations — have always been part of the natural cycle for coastal wetlands and lakeshores. The difference is felt by people with facilities at or near the lake when a change of 1 or 2 feet occurs after a prolonged period of rising lake levels, that is, when lake levels go beyond the comfortable range to which users are accustomed.
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Do high and low lake levels come in cycles?
Yes, but not in regular or predictable ones. Since the high water levels in the 1950s, there have been two high-water peaks during1973-74 and 1985-86. And, the upper Great Lakes appear to be rising to a third peak this year. In that same nearly half-century, there has been only one major below-average dip in water levels, from 1963 to 1965.
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How long will high lake levels last?
Until there is a prolonged — from months to years — shift in climate that reduces high precipitation and increases evaporation.
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How predictable are Great Lakes water levels?
Lake levels are generally and roughly predictable up to six months in advance. Methods for forecasting lake levels up to a year in advance are being developed, but they are not yet ready.
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Can't Great Lakes levels be controlled?
The levels of lakes Superior and Ontario can be adjusted but not controlled. Adjustments are made to a series of control gates in dams at the lakes’ outlets, but this only results in lake level changes of less than a foot over six months to a year.
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Are there any benefits to higher lake levels?
Higher lake levels allow for more hydropower generation at Sault Ste. Marie, the outlet of Lake Superior, and the Niagara River, the outlet of Lake Erie. Higher lake levels also allow ships to carry more cargo.
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Who is most likely to be affected by high lake levels?
Urban-area property owners with low-lying shore land that suffer flood damage. Owners of lakeshore properties with little or no beaches at high lake levels, making these properties vulnerable to direct wave attack during storms. Operators of sewage treatment facilities and operators of fixed marina docks. Commercial vessel operators who must operate at slower speeds in connecting channels to avoid wakes that will damage shore property and facilities.
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What can coastal property owners do during rising lake levels?
Frequently check for signs of bluff or bank failure and effects of storms on erodible land and shore protection structures. Check the condition of shore protection structures with a qualified contractor, and repair and reinforce the structures.
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More information about water
levels and flows in the Great Lakes Basin on 
Shore Erosion and Coastal Flooding Questions
How do high lake levels increase shore erosion?
They can have a significant effect when strong winds create large waves. High lake levels enable storm waves to run up and break higher on the shore. Some coastal areas have virtually no protective beaches at the highest lake levels. Any time the wind blows strongly toward or along the shore, storm waves break directly against the bluffs or banks on these coasts, removing soil at the bases of these slopes and making the upper portions of the slopes unstable, hastening erosion.
Shoreline erosion and flooding of Red Lantern
Restaurant
at Indiana Dunes National Lakeshore, Lake Michigan
(National Park Service photo by R. Royce, March 1972)
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What areas are most at risk for coastal flooding?
Low-lying properties, facilities, communities and roads in coastal bays where water levels during storms might rise several times higher than storm-water levels on the open lakeshore.
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Where is erosion and bluff slumping risk greatest?
Highly erodible coastal sites with few or no protective natural barriers (reefs or shoals) offshore and few or no protective beaches onshore at high lake levels.
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What can be done about shore erosion?
Where existing buildings are in danger from erosion, contact neighbors who successfully weathered the last high-water period to find out what they did that worked well to provide erosion protection.
Shore protection structures should be planned and built in concert with your neighbors’ protection efforts. Individual structures sometimes harm adjacent unprotected property. Contact an engineer to design a shore protection system or a contractor to build a shore protection structure. If planning a new building, don’t locate it close enough to the water’s edge to be threatened by flooding from extremely high lake levels during storms or by erosion over the expected life of the building.
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More information about soils,
erosion and sedimentation in the Great Lakes Region on
Severe erosion closes Oval Beach at Saugatuck, Michigan
(
Michigan DNR photo)
What kinds of shore protection
are recommended?
Good, up-to-date advice on adequate shore protection structures is hard to find because much of the information for property owners published in the 1970s and 1980s is outdated. Flexible and stable structures that have porous surfaces and slope downward to the lake seem to have a better record for adequacy than most other types of shore protection structures used on the lakes. These structures are called riprap or armor stone revetments. Unfortunately, few if any shore protection structures will last long where significant lakebed erosion occurs. Shore protection structures also are not recommended in siting new buildings because they are likely to be very expensive to build and maintain. The wisest policy is to allow erosion to continue and to site new buildings far enough back from the edges of bluffs and banks to avoid the need for shore protection structures during the lives of these buildings.
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What kinds of shore protection should be avoided?
Avoid straight, vertical walls that reflect waves without scattering the reflected wave energy. Avoid sand bags, sand-filled tubes, stone-filled wire mesh enclosures (gabions), concrete blocks, rubber tires and most other forms of low-cost shore protection where there is exposure to large waves from the open lakes.
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What are some common shore protection installation mistakes?
The most common mistake is not paying enough attention to coastal hazards in siting buildings and planning shore protection. In times of high demand for shore protection, many property owners get busy contractors to put in hastily placed windrows of low-quality stone that starts to break up in a few years. The result is temporary shore protection that becomes unstable and ineffective as it disintegrates. Make sure contractors get only high-quality stone for revetments and place it in stable positions to avoid this problem.
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If a shore protection structure isn't feasible, then what?
Relocate the building as soon as possible. Storms during periods of high lake levels can sometimes trigger massive coastal bluff slumps or cause major erosion — 30 to 50 feet or more in some places — during single storms. This sudden loss of shoreland might not leave enough room between a building and the bluff or bank edge to easily maneuver house-moving equipment.
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What do lakeshore property owners need to know?
Coastal property owners need to know how far storm water elevations can rise on the land they own. They also need to learn the past erosion history of the property, the present stability of the land at the lake edge and how long present buildings or prospective building sites will be safe from erosion.
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More information about shore protection on
Winter
storm surge along Lakefront Drive on Lake Michigan at Indiana Dunes National Lakeshore
(National Park Service photo, February 1973)
Sources of Additional Information on Great Lakes Water Levels and Coastal Erosion
UW
Sea Grant Advisory Services
Goodnight Hall, 1975 Willow Drive
Madison, WI 53706-1103, USA
Phone (608) 262-0645
Fax (608) 262-0591
Email jkeillor@seagrant.wisc.edu
See also our Coastal Engineering Web pages!
Erosion along sand banks of Lake Michigan
at Indiana Dunes National Lakeshore
(National Park Service photo, September 1972)
Additional information
on this topic is available via the Great Lakes
Information Network. See GLIN's links under Great
Lakes-St. Lawrence Hydrology.
Lake Levels Questions | Erosion & Flooding Questions | Shore Protection Questions
© 1997 University
of Wisconsin Sea Grant Institute
Written by Keillor. Webpage created 21 May
1997 by Wittman.
Photos from VISUALIZING THE GREAT LAKES: IMAGES
OF A REGION,
by Minnesota Sea Grant and U.S. EPA Great Lakes National Program Office.
Last updated 17 October 2001 by
Wittman
http://www.seagrant.wisc.edu/communications/LakeLevels/FAQ.html