As summer comes to an end, and if you enjoyed Lake Michigan this summer, you might have noticed lower water levels. While you may wonder about lower water levels, the higher water levels in the past decade continue to have a major impact.
In response to higher water levels, many property owners resorted to protecting their properties against erosion and water damage. This process is known as shoreline armoring, which refers to the construction of synthetic structures to slow or stop erosion and wave damage along the coast. But how effective are these structures and do they pose threats to the environment?
New research from Michigan State University Assistant Professor Ethan Theuerkauf, a coastal geomorphologist with the Department of Geography, Environment and Spatial Sciences, decided to document the increase of shoreline armoring in response to rising lake levels and its associated effects on coastal erosion.
The study, published in the Journal of Great Lakes Research, is the first to track the changes in the percentage of armoring, despite the prevalence of armoring throughout the Great Lakes region.
Shoreline armoring
Starting in 2014, Lake Michigan, like the other Great Lakes, experienced increasingly high-water levels, peaking in 2020. As water levels and wave energy increased during this time period, so did beach, dune and bluff erosion.
For home and business owners, as well as lakefront communities, the desire to protect their properties increased. In many instances, coastal property owners responded to these hazards by using a variety of hard structures, such as seawalls, revetments and groins.
- Groins are shore-perpendicular structures that are built to trap sand that is moving along the coast and slow beach erosion.
- Seawalls are concrete, steel or wood walls that are built along the shoreline to stop erosion of the beach or bluff.
- Revetments are like seawalls in that they are built along the shoreline to slow or stop erosion but are built to mimic the slope of the coast rather than being a vertical wall. The aim of this is to disperse the wave energy rather than deflecting it down to the lakebed, which can cause more problems.
While these structures can successfully prevent water damage, there are other unintended consequences, such as disrupted sediment transport or harm to the environment.
Study background
Theuerkauf focused his study on the entire open-coast shoreline of Michigan’s Lake Michigan coast, extending from the Indiana state line north to the Straits of Mackinac, a distance of nearly 370 miles.
The extent of shoreline armoring prior to the high-water period beginning in 2014 was determined using datasets through the National Oceanic and Atmospheric Administration’s, or NOAA’s, Office for Coastal Management and digitized coastal imagery from 2014. These datasets were compared to a 2021 map of armored shoreline Theuerkauf created using Google Earth Pro.
After analyzing the data, Theuerkauf determined that shoreline armoring had increased fivefold during the period of high-water levels. The southern section saw the most armoring with an increase of 351% between 2014 and 2021. The middle section had the next highest increase, with 5,195 meters (around 3 miles) of shoreline armoring in 2014 before increasing to 28,268 meters (just under 18 miles) by 2021. The northern section had 1,754 meters (around 1 mile) of shoreline armoring in 2014, which increased to 8,945 meters (around 6 miles) in 2021.
In total, the amount of armored shoreline increased 376% from 23,421 meters (around 15 miles and 4% of the coast) in 2014 to 111,458 meters (around 69 miles and 19% of the coast) in 2021.
“Despite the protective intent, this widespread armoring raises concerns about its long-term effects on coastal ecosystems and geomorphology, highlighting the need for further research and informed policy decisions to balance protection needs with ecosystem function and integrity,” Theuerkauf said.
Theuerkauf’s study found that the increase in shoreline armoring can lead to negative impacts on the coast, making it important to understand the extent of armoring in response to higher lake levels to inform policy management actions.
