Artificial Reefs Can Mitigate Coastal Erosion in the Great Lakes. Will Cities Agree to Adopt Them?

Illinois boasts 63 miles of coastline along Lake Michigan’s southwestern shore, nearly all of which is fortified by metal breakwaters, concrete seawalls and even swaths of land built out into the lake.

These structures are meant to protect the city of Chicago and its suburbs from coastal erosion. But according to Hillary Glandon, a scientist at the Lake Michigan Biological Station in Zion, Illinois, this fortification is “part of the problem.”

“You have protection structure after protection structure after protection structure, and it has really disrupted the natural flow and processes that occur in these coastal zones,” Glandon said. 

With water levels that can vary by several feet from year to year—and climate change making these variations even more unpredictable—cities across the Great Lakes are working to fortify their coastlines and prevent erosion. But traditional coastal infrastructure like breakwalls can cost tens of millions of dollars, making them a heavy financial lift for local governments. And while these breakwalls help retain sand and build up the coastline directly inland of where they’re constructed, they also block currents from carrying sediment farther down the coast, compounding the effects of erosion downstream.

Glandon and her team have a solution: Install artificial reefs in the lake’s shallows to temper the intensity of waves and preserve the shoreline directly inland. Through two federally funded pilot projects, the team is studying two artificial reefs—one at Illinois Beach State Park in Zion, and another at Fort Sheridan in nearby Highland Park. They’re hoping to collect data on how these reefs impact the local shoreline to see if artificial reefs are a scalable solution to coastal erosion in the Great Lakes.

“This project was hoping to come up with some softer designs, not necessarily fully stopping that movement of sand and water, but also a more cost effective design,” Glandon said. The two reefs she’s studying are both made entirely of natural materials and built by the U.S. Army Corps of Engineers. The reef at Fort Sheridan was built in 2020, while the one at Illinois Beach State Park was built the following year, designed as part of the University of Pennsylvania’s Healthy Port Futures program. Their approach, called “rubble ridges,” involves building limestone reefs close to shore, redirecting wave energy and retaining sand.

While artificial reefs have been used around the world to bolster biodiversity, their use for erosion control is new. Lake Michigan is already home to a handful of artificial reefs, most of which are located farther from shore as a habitat for marine life. 

Some researchers in the U.S., though, say these could serve the dual purpose of boosting fish populations and preventing erosion, disrupting waves so that they’re less intense when they crash ashore. 

“It’s a hydrodynamic optimization to get the wave energy that’’s coming into these reef structures,” said Ansel Garcia-Langley, a graduate student at the Massachusetts Institute of Technology who’s working on another architected reef design. “As the waves hit these pillars, it forces the waves into different directions, so that they spin off into these vortices. So a lot of the energy coming in is dissipated in on itself.” 

Garcia-Langley and his colleagues at MIT wrapped up their initial study of architected reefs last March, and found promising results. His team, headed by ocean science and engineering professor Michael Triantafyllou, created a unique cylindrical reef design that is intended to maximize drag on wave energy, forcing the waves through cracks in the structure to lower that energy before it hits the coast. 

Reefs like these help preserve the natural flow of sand and sediment along coasts. Structures like seawalls can create what Garcia-Langley called “dead zones,” where this flow reaches a standstill, redirecting increased wave energy to the surrounding areas. 

For local governments jockeying for control over the Lake Michigan shoreline, avoiding these dead zones is critical.

“The lake is valuable, right? People want to live near the lake. They want to be able to go to the beach,” Glandon said. “And so removing that possibility from a landowner due to actions upstream tends to cause some real tension.”

In Illinois, there are dozens of municipalities that border Lake Michigan, and hundreds of private landowners. Because the towns and property owners with a slice of that shoreline control their own infrastructure, shoreline protection can get heated. Sediment flows from north to south in Lake Michigan, so when one town installs a seawall, it can prevent sediment from reaching shores directly south, leaving those places more vulnerable. 

This has led to heated debate between some shoreline towns, said Cody Eskew, a specialist in coastal studies with the Illinois Sustainable Technology Center. Eskew, who works closely with the Illinois Department of Natural Resources, has helped run IDNR’s Shoreline Management Working Group since 2015, holding biannual meetings with local governments who share Lake Michigan’s coastline to work through their shoreline protection plans.

“At first, I think there was just a lack of understanding of what the shoreline dynamics were in our region, especially the North Shore region,” Eskew said. “At Illinois Beach State Park, there’s a ton of sand there, but when you go a little bit farther south toward those North Shore neighborhoods, we found that there’s just not much naturally occurring sand on that piece of the shoreline. So communities are really limited in terms of, you know, what they can expect from their neighbor and getting sand from updrift.” 

That makes artificial reefs particularly alluring in the Great Lakes—they’re a way to block wave energy without making erosion worse for neighbors, and they’re far cheaper than traditional infrastructure. For instance, the Illinois Department of Natural Resources recently funded a project building 22 breakwalls off the coast of Illinois Beach State Park, which cost about $73 million. Installing the beach’s rubble ridges cost $1.4 million, according to Eskew. 

“The typical community is not going to have in their capital budget to be able to install something that large,” he said of the breakwalls. “So they are really looking into those more hybrid structures.”

The costs aren’t set and can vary widely, said Juliet Simpson, a coastal ecologist with MIT’s Sea Grant program who also works on their architected reefs project with Garcia-Langley. Last year, the team estimated their model to cost about $6 million per mile, while Simpson noted that other reef models can cost upwards of $10 million per mile. The team is hoping to slash that cost even further to make these protections affordable for coastal communities.

So what’s keeping this new approach to artificial reefs from taking off? According to Sean Burkholder, who heads the UPenn Healthy Port Futures team that helped design the rubble ridges, it’s simply a lack of familiarity.

“We’ve lived on shorelines that have been protected by seawalls for hundreds of years, and we kind of know that they work,” Burkholder said. “We also kind of know when they fail, and how they’re going to fail. Any type of nature-based infrastructure, they’re not super well proven.”

To prove the concept, Glandon and her team are meticulously collecting data on how the artificial reefs at Illinois Beach and Fort Sheridan impact their respective shorelines over the course of five years. 

The data is already showing promising results—and according to Eskew, it’s been drawing attention from officials working on shoreline management all over Lake Michigan. If all goes well, these rubble ridges could soon appear beneath the surface of many of the Great Lakes.

“Often these types of structures are built, and there’s very few requirements for post construction monitoring.” Glandon said. “I think this is a really quantitative picture of shoreline change and aquatic habitat creation as a result of these nearshore breakwaters.”