WATCH: Living shoreline project aims to prevent erosion, provide habitat in Apalachicola Bay
A day after Florida experienced its second major hurricane in two weeks, I was shown one of the less dramatic – but not unimportant – effects of one of those storms.
Two weeks earlier, Hurricane Helene veered east, sparing Apalachicola Bay a direct hit. When a hurricane enters the Gulf, what we most fear and pay attention to is the eye of the storm. And rightfully so. We’ve seen the damage caused by a storm’s strongest winds and waves. Many of the people reading this have experienced it directly.
As we zoom out from the worst of it, we can see that the storm surge of a hurricane affects all of the Gulf coast in some way. Helene caused flooding and damaged homes in coastal areas over 100 miles from where it made landfall. Further out, the effects were more subtle, and will likely be felt more in the long term. It will be felt in every grain of sand that washed away.
The National Oceanic and Atmospheric Administration (NOAA) estimates that coastal erosion is responsible for about $500 million dollars of property damage annually in the U.S. It’s not near the cost of 2024’s two major storms, Helene ($78.7 billion) and Milton ($34.3 billion), but it’s not insignificant.
Coastal ecosystems prevent erosion by holding sediments, but in much of Florida, buildings and roads have replaced marshes and mangroves. That’s why, in one such stretch of U.S. 98, the Apalachee Regional Planning Council (ARPC) has installed a “living shoreline” to specifically address erosion. Hurricane Helene tested the effectiveness of the system.
Protecting Scenic Highway 98 in Franklin County
In 2020, I visited a nearby stretch of this highway with FSU oceanographer Dr. Jeff Chanton. Parts of the road had washed away during Hurricane Michael, and had been replaced. He showed me where, a year later, a smaller storm had caused the shoulder to erode away.
In Franklin County, Highway 98 hugs the coast. As we drive, we may see dolphins, diving pelicans, eagles and ospreys perched in trees. It’s scenic, but exposed. If we drive over the Ochlockonee River bridge into Wakulla County, the road runs behind the St. Marks National Wildlife Refuge, and thousands of acres of salt marsh habitat. That marsh protects the coast from day-to-day wind and waves, and offers from storm surge.
Using relief dollars from Hurricane Michael and the Deepwater Horizon Oil Spill, in 2019 the ARPC started looking at sites where they could install living shorelines along the more exposed stretches of 98. The site we visited is phase one of the project.
“This project is intended to cut down on the day-to-day the chronic erosion,” said Josh Adams. He’s ARPC’s Environmental Planning Manager. “It’s not going to stop a category-three storm.”
It takes time to see how effective this kind of system is at mitigating erosion, but Helene gave us an accelerated look. After 3-5 feet of storm surge washed over the system, it captured about a foot of sand. It seems like a small thing, but it shows what the system can do.
How does a living shoreline protect the coast compared to something like a seawall?
It’s the difference between brute force and friction.
I learned about this after a visit to the University of Miami’s SUSTAIN Lab. People kept telling me that coastal ecosystems were more effective at protecting the coast than seawalls, and I wanted to know if that was true, and if so, why. Using a hurricane simulator that generates category-five conditions, SUSTAIN studies the physics of waves and how they interact with different surfaces.
Before we take a closer look at how the Apalachicola Bay system was constructed, I’d like to review some of what I learned at SUSTAIN: the basics of wave motion and its interaction with the coast.
The Physics of Waves and the Texture of the Coast
- Seawalls may protect the land behind them, but they don’t remove any energy from a wave. Instead, waves are reflected from hard, flat surfaces with their energy intact. This could send destructive wave energy elsewhere on the coast, and it causes erosion in nearby areas.
- Barrier islands protect a coastline, but their soft, sandy surfaces don’t reflect waves. They absorb the hit, and they heal. They are always changing shape; sand will wash away in one place and collect in another. Many of Florida’s barrier islands are built up with human structures, hardening what had been a shifting landscape.
- Salt marshes, intertidal oyster reefs, and mangroves slow wave action through friction. Marsh cordgrass (Spartina alterniflora) or oysters act like velcro on a wave, the myriad individuals destabilizing wave action. Seagrasses and coral reefs affect the below-the-surface part of the wave energy. This doesn’t mean a salt marsh or seagrass bed will halt a category-five storm, but it will slow storm surge and protect the coast from waves.
In this video, I mention a solution developed by the SUSTAIN Lab called SEAHIVE. SEAHIVE is a concrete hexagonal tube system that can be configured in different ways. Large holes in the tubes cause friction, and can be used as planters for cordgrass, mangroves, or corals. The hard surface of the tubes could also recruit oysters. In theory, the system could become a coastal ecosystem over time.
SEAHIVE is currently being tested at a few locations in South Florida. I wanted to introduce it here because it has some similarities to this Living Coastline, and I thought it would be instructive to compare and contrast the two.
The Design of the Apalachicola Bay Living Shoreline- Phase 1
“The living shoreline concept has really got two main components, especially for our design,” said Will Mather. He’s an Environmental Scientist with WSP in the US, an engineering form specializing in sustainable projects. He designed the Apalachicola Bay system. “We have the marsh and the reefs. As the waves come crashing into the shore here, they hit the reefs first, get slowed down, and then they hit the marsh. And the marsh is what pulls the last bits of energy out and settles down the sediment.”
I visited with Josh and Will at low tide, which allowed us to walk around. It also kept me from seeing the system in action, so I returned at the midway point between high and low tide. That day, I could see white-capped waves hit the outer reef structures. Behind them, calmer waves drifted into reefs and marshes.
Let’s break down the living shoreline into its components:
1. Reef Balls
The instant I saw the reef balls, I thought of the SEAHIVE. Both have holes to cause friction on waves, and both can serve as a landing spot for oysters. Their different shapes of each system might make one or the other a better fit at different types of sites. For instance, SEAHIVE has been installed where seawalls have traditionally been used in large coastal cities. It has also been deployed off the coast of Miami Beach, fully submerged.
Reef balls look more at home on this living shoreline, in which the reefs have an organic shape. The look of the project was factored into the design. This section of U.S. 98 is part of the Big Bend Scenic Highway, and the living shoreline has to be incorporated into the scenery.
As we walked by the reef balls, we could see oysters had settled on them, both inside and out.
2. Rock Reefs
Oysters had also settled on the rocks they used to build the other reef structures. The texture of the rocks is intended to break waves, but the hope is that oysters will use the rocks as a substrate to build a living reef. As we walked, Will noticed that, “on some of these smaller pieces nestled in on the larger ones, the oysters have started to cement the reef together.”
A moratorium on harvesting Apalachicola oysters will end in December. The most harvested oysters in the bay are subtidal – always submerged. The oysters here are intertidal, which are exposed at low tide. While the oysters on this one site may not be a major factor in the recovery of the Apalachicola Bay oyster fishery, Will said that the fact that oysters are settling here is a good sign.
“We’re not spat-limited in the system,” Will said. “So that means when we put structure out like these reefs, over time, they will be naturally seeded, which is fantastic. There’s other systems around the US that are a little worse for wear because they don’t have that natural spat accumulating in their bays.”
3. The Layout of the Reefs
The reefs could have been laid out in a single, continuous line. The gaps between the reefs have a specific purpose.
“You’ll notice that there’s about a five foot wide break in between the reefs,” Will said. “That’s to allow for ingress and egress of manatees, dolphins, turtles.”
One reason those animals would venture behind the reefs is food. The salt marshes ARPC planted, and the oyster reefs forming on the rocks and reef balls are estuary ecosystems. Another estuary ecosystem was already present at the site, and that also affected the design of the reefs.
“We kind of had to adapt our reef design to mirror the shape of the seagrass beds,” Will said. They mapped the shape of the beds into a Geographic Information System (GIS) model to design the reefs around them. When they started construction, however, they found that the beds had moved and changed shape. “That’s what led to me and my team going out and actually designing these reefs all by hand.”
4. Seagrass Beds
Seagrass beds provide some of the same functionality as salt marshes. They both hold sediments with their roots, and they both filter pollutants from the water. Seagrass blades can slow waves action below water similar to marshes at the water’s surface. And, again, it is an estuary ecosystem.
Estuaries occur where a saltwater body meets land, often near a freshwater input like a river. They’re places where we find seafood species, either as larvae or juveniles seeking shelter or as adults on the search for food. The Florida Fish and Wildlife Conservation Commission estimates that 70% of commercially or recreationally fished species make use of estuary ecosystems.
5. Salt Marshes
The salt marsh is what Will calls the catcher’s mitt. It’s the component of the system that they intended to hold sediments. Marshes accumulate sediments from stormwater runoff coming from land. Also during a storm, as waves push sediments towards land, grasses catch sediment as the waves retreat.
I didn’t see the marshes grabbing sediment on my visits – can you see that with the naked eye on an average day? What I did see is that the marsh had accumulated dead seagrass and other vegetative matter. ARPC planted the marsh cordgrass in sand. Pure sand is nothing more than ground up rock. As that organic matter decomposes, though, it will turn into the muck we find in a natural marsh.
Marsh mud is the equivalent of topsoil in this habitat. It provides nutrients to the grass, and is home to many small critters. Invertebrates, of course, feed animals throughout the food web, and I could see plenty of wading birds and terns hunting for food, mullet jumping, and fiddler crabs colonizing the marsh.
Meet the Plants and Animals in North Florida’s Estuaries
When the WFSU Ecology Blog started in 2010, our focus was entirely on marine biology. The following pages helped us introduce the many plants and animals featured in the research we covered.
How Will the Apalachicola Bay Living Shoreline Grow Over Time?
Marsh cordgrass expands via rhizomes, an individual plant spreading as much as ten to twelve feet a year. Portions of the marsh may die as seagrass wrack lands on it at the end of summer, when new seagrass growth pushes out dead leaves. Will and Josh expect that a strong storm might further alter the shape of the system.
“The marsh will change over time,” Will said. “The seagrass obviously changes extremely rapidly… So the system is extremely dynamic. And we anticipated that. We anticipated some of these reefs getting buried and some of them getting unearthed again. It’s all part of the plan.”
The project itself is expanding as well. This site was phase one of three; the second site will be installed in front of Tate’s Hell State Forest. Apalachee Regional Planning Council is also looking west of Apalachicola for living shoreline sites unrelated to this project.
As with any restoration project I cover, I wonder what this will look like in 10-15 years, and beyond. Multiple sites, each with a few years to reshape themselves and perhaps lose the look of a human-made system. At that point, it would be easier to measure the effectiveness of the systems. It will be measured in the amount of sediment the systems gather, the richness of wildlife, and how far they grows outward – much of which you can gauge as you drive by it on the way to the beach.
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