Coastal hazards impact bluff, beaches, and coastal infrastructure
The Lake Michigan coast is composed of bluffs, beaches, and waterfront infrastructure. These interconnected coastal features serve as the interface between high-value upland areas and the economic and cultural assets of Lake Michigan. Processes like waves, erosion, sediment transport, flooding, slope stability, and fluctuating lake water levels can combine to damage coastal properties and impair the function of waterfront facilities.
The hazard processes that affect bluffs, beaches, and waterfront infrastructure are described briefly below. For more detailed information on these issues, an excellent review of hazard processes is available in the U.S. Army Corps of Engineers/Wisconsin Sea Grant publication Living on the Coast.
Shoreline Recession and Bluff Failure
Coastal Assets at Risk
Wisconsin’s Lake Michigan bluffs are home to residential, commercial, and industrial properties with scenic views in close proximity to the lakefront. In Wisconsin’s Lake Michigan coastal counties, $11.74 billion of improved property is estimated to be within a quarter mile of the coastal area boundary (WEM, 2021).
Hazard Processes
Waves can erode the shoreline, causing it to recede landward. Shoreline recession along bluff coasts is caused by a cycle of erosion at the base of the bluff by waves, which can destabilize the bluff slope and cause failure, or collapse, of the bluff. High Lake Michigan water levels allow erosive waves to reach higher elevations on the shore, accelerating shoreline recession and bluff failure processes. Other factors that contribute to bluff failure include elevated groundwater, which reduces the stability of the slope; stormwater runoff, which erodes the bluff surface soil: and freeze-thaw cycles, which weaken the soil.
Beach Erosion
Coastal Assets at Risk
Wisconsin has 110 public access beaches (DNR, 2021), which provide valuable recreational lake access to millions of visitors per year, a significant driver of a tourism economy that brings $35 to $50 to the local economy per beach visitor (Song et al., 2010).
Hazard Processes
Waves can erode beach sand, leading to a narrower beach. High Lake Michigan water levels inundate portions of the beach while also allowing waves to erode higher up on the beach. Beach erosion can be accelerated by the interruption of sediment transport along the coast by increased armoring of the shoreline. In addition to erosion, beach function can also be impaired by water quality issues.
Port, Harbor and Marina Damage and Navigation Impairment
Coastal Assets at Risk
Wisconsin is home to commercial ports, recreational harbors, and numerous marinas, which contribute hundreds of millions to Wisconsin’s economy through commerce (Martin Associates, 2018) and tourism (Southwick Associates, 2020).
Hazard Processes
Low water levels and sediment deposition can lead to insufficient water depths for safe navigation at these facilities, requiring costly dredging to maintain function. Low water levels also expose normally submerged timber and rock infrastructure to air, accelerating the deterioration of these materials. High water levels and large storm waves can damage or destabilize infrastructure. Both low and high-water level extremes can lead to operational and safety issues if a large elevation difference exists between vessel and dockage.
Coastal Flooding
Coastal Assets at Risk
Many of today’s coastal cities occupy low-lying areas like river mouths and natural harbors that provide valuable access to the lake for commerce and water infrastructure. In other low-lying coastal areas, only a beach, dunes or low banks lie between the lake and residential or commercial development.
Hazard Processes
Coastal storms with strong winds and atmospheric pressure gradients cause large waves and a “piling up” of water along the coast known as a storm surge, which can combine to inundate low-lying areas of the coast. High lake water levels will contribute to an increase in coastal flooding by allowing waves and storm surge inundation to reach higher elevations.
The Interconnected Coast
Bluffs, beaches, and waterfront infrastructure are interconnected through regional sediment transport and nearshore processes like waves and currents. Oftentimes, actions taken to reduce risk at one location on the coast can produce unintended negative consequences at surrounding areas. For example, armoring the shoreline at one property to protect against erosion changes the sediment and wave dynamics of the area and may cause an increase in erosion to nearby shorelines. The complexities of the bluff-beach-infrastructure shoreline system in Wisconsin illustrate how uncoordinated actions to reduce risk locally can lead to exacerbated issues regionally.
References
- Martin Associates. 2018. The Economic Impacts of Maritime Shipping in the Great Lakes-St. Lawrence Seaway Region. Retrieved from: https://greatlakesseaway.org/wp-content/uploads/2021/07/2018-glsls-study-en-hr.pdf
- Song, F., Lupi, F., and Kaplowitz, M. 2010. Valuing Great Lakes beaches. Agricultural & Applied Economics Association Meeting, July 25-27, 2010.
- Southwick Associates. 2020. Sportfishing in America: A Reliable Economic Force. Produced for the American Sportfishing Association by Southwick Associates via Multistate Grant #F20AP00183 awarded by the Wildlife and Sport Fish Restoration Programs of the U.S. Fish and Wildlife Service. Retrieved from: https://asafishing.org/wp-content/uploads/2021/11/Sportfishing-in-America-Economic-Report-March-2021.pdf
- Wisconsin DNR (DNR). 2021. 2021 Wisconsin Beach List. Retrieved from: https://dnr.wisconsin.gov/sites/default/files/topic/Beaches/2021BeachList.pdf
- Wisconsin Emergency Management. 2021. State of Wisconsin Hazard Mitigation Plan. Retrieved from: https://wem.wi.gov/state-planning/
