Future Seawalls: Higher, Stronger and Better for Marine Life

By Alex Harris | April 18, 2022

MIAMI (AP) — Seawalls, despite more natural innovations like “living” shorelines, aren’t going anywhere in Florida — except up.

With thousands of miles of coastline facing two feet of sea level rise by 2060, some cities and counties, including Miami-Dade, are already calling for raising the standard heights of seawalls. And many of the seawalls to come in the decades ahead promise to be different — not only stronger and more durable, but better designed to both absorb waves and reduce damage to the adjacent sea or bay bottom.

One new approach in development by the University of Miami is even specifically designed to provide habitat for corals, mangroves and other marine life.

“We’ve got to stop doing things the way we have for the last few decades,” said Esber Andiroglu, an associate professor at the University of Miami focused on building the seawalls of the future. “This is a time for innovation,”

He’s among the university scientists and private companies designing new technology to improve seawall construction, which is likely to be a booming business in coming decades. By one estimate, it could cost $75 billion to raise and repair every existing wall in Florida by 2040.

Harder, Better, Faster, Stronger

The first thing you’d notice about the brand new seawall alongside North Bay Village’s Treasures on the Bay Condominium is that it’s higher than it used to be. The other major change is impossible to detect because it’s encased in concrete.

About 50 feet of the seawall cap isn’t interlaced with the usual steel rods, known as rebar, that reinforce the vast majority of buildings. Instead, it uses bars of glass fiber reinforced polymer. It’s twice as strong as steel, weighs about 75% less and most importantly, it doesn’t corrode.

That’s a common weakness with rebar used in projects exposed to salty air and water. It’s why so many older coastal buildings start to sport menacing cracks if left unattended.

“Reinforcement with fiber polymers would completely take that problem away,” said Andiroglu, who designed the new seawall. The polymer rebar is well-tested, he said, and increasingly used by the Florida Department of Transportation on projects vulnerable to salt air.

The upfront cost is about 10% to 15% higher than steel, he said, but over the long term it will be cheaper because it has a far longer life span — 100 years or more, some studies suggest. And the price is likely to decrease as its use becomes more common.

Seawalls designed like LEGO bricks also could help reduce the costs of raising them in the future. Andiroglu’s lab is experimenting with modular pieces that could be added to as needed. That could be handy as rising sea levels push coastal building codes higher.

“People always say `but if I built it too high I’m wasting my views,’ and `it’s not going to happen during my lifetime,’ ” he said. “Modular functions allow people to add height to seawalls as it’s happening. It will also break down the financial burden across decades.”

Coral Friendly Concrete

The primary ingredient of seawalls — concrete — is also ripe for change. It’s a big contributor to carbon dioxide emissions, which exacerbate climate change, and it can deteriorate in humid, salty environments like South Florida.

“Concrete is pretty much the most used material in the world,” said Prannoy Suraneni, an assistant professor at UM dedicated to coming up with better concrete _ not just for engineering but also for the environment.

Suraneni said it’s relatively simple to switch out ingredients in concrete to make it more durable. There is already an option called ultra-high-performance concrete, and builders across the country are starting to use it more but it doesn’t solve every problem, especially on the environmental side.

“How we make concrete resilient or coral friendly, that is a lot more challenging,” he said.

Research already shows that a seawall with a variety of textures will attract different forms of marine life better than a completely smooth wall. His team is also studying how the chemical composition of different concrete mixes — alkalinity and other additives — encourages healthier growth of marine life, a still unresolved question.

Perhaps the most revolutionary change would be using saltwater, rather than fresh water in concrete seawalls — a change that would cut costs and would be especially valuable in countries where drinking water is depleted.

After several years of research and experiments, Suraneni said he’s confident that seawater can be used in concrete, as long as the steel rebar inside is also swapped out. Steel and salt just don’t mix.

“There is zero question you can use seawater in concrete. The main issue is the steel we use in concrete is likely to corrode,” he said. “So don’t use steel in these circumstances. Use glass fiber reinforced polymer.”

Introducing Seahive

While seawalls protect land, they aren’t so good for marine life. When a wave comes crashing into a mangrove forest, or even a pile of rocks, it breaks up that force. But when a wave crashes into a straight seawall, all that energy gets funneled straight down, scouring the adjacent sea bottom and sea life.

In Miami-Dade, that’s why new seawalls are required to have a pile of rocks _ known as riprap _ at their base. In some spots, the rocks are piled high enough to peek out of the water, and mangroves and other coastal plants will root there.

That’s what inspired a group of UM scientists to design a riprap replacement, designed with mangroves and other plant life in mind. They call it SEAHIVE, a reference to the six-sided tubes that stack up to look like a beehive honeycomb.

“Think of it as an airbag. It dissipates the energy by allowing the water inside,” said Landolf Rhode-Barbarigos, an assistant professor at the University of Miami’s college of engineering and head of the research team at SEAHIVE.

After three years of testing the structures in water tanks, the team is moving on to pilot projects in the real world. One will be placed near a seawall in North Bay Village, another will be offshore in Miami Beach as an artificial coral reef, and a third will be debuted this summer in Pompano Beach for a snorkel park project called Wahoo Bay.

The plan is to plant mangroves and coral on the SEAHIVE structures in the sunken park so residents _ especially kids _ can swim up and experience nature firsthand.

“We expect the major attraction will be school groups,” said Rob Wyre, chairman of Shipwreck Park, creator of another snorkel park in Broward County. “It’s a blank canvas insofar as what’s going to happen on the education side.”

Once they’re in place, Rhode-Barbarigos said his team will measure everything from how fish and plants react to how good of a job the structures do at breaking up waves. To guard against corrosion and crumbling, they’ll be built with the same plastic polymers as the North Bay Village condo seawall. If all goes well, he said this technology could be an easy-to-deploy solution for waterfront South Florida cities.

“We wanted something which is robust, which is easy to implement, easy to manufacture, approachable,” he said. “You can always push the envelope to really high-tech later. We need the low-tech solution so we can have sustainable, equitable development.”

About Alex Harris

Harris wrote this for the Miami Herald.

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