Resources for Great Lakes Shoreline Erosion Control Projects
The Lake Michigan and Lake Superior shorelines are critically important spaces for fish and wildlife habitat and recreational use. Great Lakes shorelines have many coastal influences that make them more like oceans than our thousands of inland lakes. The DNR understands landowner and municipality concerns about structures that may be at risk from bluff and dune erosion on the Great Lakes and recognizes the large investments residents have in their homes. Projects must be done in a way that minimizes lakebed fill and impacts to nearshore areas and adjacent properties.
Designing and implementing a shoreline protection project involves a complex engineering analysis of water level changes, wave heights, storm surges, lakebed analysis, sediment sampling, and potential impacts to adjacent properties. State law requires DNR authorization for any material placed in Lake Michigan and Lake Superior. Additional DNR permits may be needed for grading and dredging associated with a shoreline erosion control project.
*The DNR highly recommends that property owners seek experienced coastal engineering professionals when considering a Great Lakes shoreline protection project.
To review permitting options, see Shoreline Erosion Control Permitting.
To start a permit application, use DNR Water ePermitting System.
Great Lakes Coastal Processes
GREAT LAKES WATER LEVELS
Each of the Great Lakes has an annual water level cycle driven by snowmelt, precipitation, and evaporation. In general, the lakes are at their lowest levels in the winter and highest levels in summer. The annual change in water levels is from 11 to 20 inches. In addition to annual changes, long-term lake levels fluctuate on a 10-year to 30-year cycle. On Lake Michigan, the difference between the record low and high water levels is greater than 6 feet.
See the USACE Weekly Great Lakes Water Level Update for current water levels on Lake Michigan and Lake Superior.
EROSION AND BEACHES
Erosion occurs when wave energy moves material away from shore to greater water depths. Erosion on the Great Lakes occurs even during low water levels. As wind blows across the surface, energy is transferred to the water and builds waves. As the wind blows across many miles of open water, it drags some water towards the downwind side of the lakes, causing a rise in water level along the downwind shore and a lowering of water on the upwind shore. Storm surges typically raise the water level one to two feet on the open coast and two to five feet in bays. Rising lake levels and lakebed erosion (reflected wave energy causing lakebed downcutting) create deeper water near shore and allow more wave power to hit shore. Falling lake levels have the opposite effect.
Changes in a beach shoreline are caused by sand starvation. Waves usually approach a beach at a slight angle, creating a “push” against the beach in the alongshore direction and moving sand laterally, known as littoral drift. When waves strike the shoreline straight on, sand is carried onshore with a wave and offshore with the undertow. This sand can be trapped by intrusions along the shoreline but will continue to move with high waves. If the nearshore area is deep enough or the undertow is strong enough, the sand can be moved into deeper water where it settles on the lakebed beyond wave movement and the sand may be lost to littoral drift.
The most effective shoreline protection structure is the simple beach. Its shallow sloping surface causes waves to break gradually. Structures and naturally steeper slopes can create wave run-ups that are twice the height of offshore waves. For beaches to be self-sustaining, there must be a source of sand from the updrift area that is not obstructed from wave action
Beach nourishment is a human-made addition of the sand in the littoral drift system. Rather than let calm water build up the beach, sand is intentionally placed on the beach. Beach nourishment is typically ongoing in order to be effective in the long-term. Planted vegetation such as dune grass, wheat, wild rye, and shoreline tree species such as willows, cottonwood, and basswood can be planted to stabilize a sand beach.
EROSION AND BLUFFS
A coastal bluff on Lake Michigan or Lake Superior is susceptible to erosion and failure due to structures constructed on the bluff top, annual freezing and thawing, groundwater action in the bluff, and the slope of the bluff face. The glacial till soils of coastal bluffs are also susceptible to erosion from waves. Erosion at the base of the bluff, known as bluff toe erosion, can over time cause slumping. High water levels and continued slumping exposes more of the bluff to wave energy and can lead to bluff failures. Many property owners on the Great Lakes look to protect the toe of the bluff from erosion by constructing riprap (revetments), using large rocks, granite blocks or other material laid over filter fabric and stone. The most effective revetments are designed with the first layer of rocks trenched into the lakebed, stone high enough to prevent overtopping during storm events, and at least two layers of outer layer stone.
For more information on coastal processes and hazards, see Resources for Property Owners | Wisconsin Sea Grant.
GREAT LAKES SHORELINE PROTECTION PROJECTS
MATERIAL TYPE AND SHAPE
The types of material used determines the longevity of a shoreline protection structure. Demolition debris like cinder blocks, concrete rubble and dirt are not acceptable materials since when they exposed to wave action and thaw and freeze cycles can crack and break apart easily. Any armor layer must be sufficiently sized to be stable and made of materials that will not crack and fragment.
The shape of the materials is also an important design consideration. Multi-faceted boulders with round surfaces work better than flat stone. Flat surfaces reflect wave energy resulting in scouring at the base of the structure, may increase wave run-up, and generally cause more erosion.
CONTRACTING WITH A COASTAL PROFESSIONAL
The cost of planning, designing, and installing shore protection structures is likely to be expensive. To help ensure a lasting investment, the DNR encourages landowners to seek experienced coastal engineering professionals to assist with your project. Coastal engineering professionals have the expertise necessary to influence the success of a shoreline project, including:
- Navigating the permit process
- Assessing the impacts of the planned project on adjacent properties
- Minimizing construction and maintenance costs
- Managing the performance and longevity of the project
Coastal professionals can also monitor the project after it is implemented and manage any modifications or repairs needed after storm damage. An investment in the services of experienced professionals is the best way to ensure the long-term success of a shoreline protection project and minimize costs during the period of ownership.