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Future levees: higher, stronger and better for marine life

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Levees, despite more natural innovations like “living” shorelines, go nowhere in Florida – except uphill.

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 increased standard levee heights. And many of the breakwaters to come in the coming decades promise to be different – not only stronger and more durable, but better designed to absorb waves and reduce damage to the adjacent sea or bay floor.

A new approach being developed by the University of Miami is even specifically designed to provide habitat for corals, mangroves and other marine life.

“We have to stop doing things the way we have done for the past few decades,” said Esber Andiroglu, an associate professor at the University of Miami who specializes in building the levees of the future. “Now is the time to innovate”

He is among university scientists and private companies designing new technologies to improve levee construction, which is expected to be a booming business in the coming decades. According to one estimate, it could cost $75 billion to raise and repair all existing walls in Florida by 2040.

HARDER, BETTER, FASTER, STRONGER

The first thing you’ll notice about the brand new seawall along the Treasures on the Bay Condominium in North Bay Village is that it’s taller than it was before. The other major change is impossible to detect because it’s locked in concrete.

About 50 feet of the levee cap is not interwoven with the usual steel rods, called rebar, which reinforce the vast majority of buildings. Instead, it uses fiberglass reinforced polymer bars. It is twice as strong as steel, weighs approximately 75% less and above all, it does not corrode.

This is a common weakness with rebar used in projects exposed to salty air and water. This is why so many older coastal buildings begin to show menacing cracks if left unattended.

“Reinforcement with polymer fibers would completely eliminate this problem,” said Andiroglu, who designed the new seawall. Polymer rebar is well tested, he said, and increasingly used by the Florida Department of Transportation on projects vulnerable to salt air.

The initial cost is about 10-15% more than steel, he said, but in the long run it will be cheaper because it has a much longer lifespan – 100 years or more. , according to some studies. And the price is likely to come down as its use becomes more common.

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

“People always say ‘but if I build it too high I’m wasting my views’ and ‘it won’t happen in my lifetime,'” he said. “The modular features allow people to add height to the dikes as they go. It will also reduce the financial burden over several decades.

CORAL-FRIENDLY CONCRETE

The main ingredient of dikes – 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 widely used material in the world,” said Prannoy Suraneni, an assistant professor at UM dedicated to finding better concrete, not only for engineering, but also for the environment. .

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

“How to make concrete resilient or coral-friendly is much more difficult,” he said.

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

Perhaps the most revolutionary change would be to use salt water rather than fresh water in concrete dykes – a change that would reduce costs and be particularly useful in countries where drinking water is depleted. .

After several years of research and experiments, Suraneni said he was convinced that seawater could be used in concrete, as long as the steel rebars inside were also replaced. Steel and salt just don’t mix.

“There is no doubt that you can use seawater in concrete. The main problem is that the steel we use in concrete is susceptible to corrosion,” he said. “So don’t use steel in these circumstances. Use fiberglass reinforced polymer.”

PRESENTATION OF SEAHIVE

Although seawalls protect the land, they are not so good for marine life. When a wave crashes into a mangrove forest, or even a pile of rocks, it breaks that force. But when a wave crashes into a straight levee, all that energy is channeled downward, eroding the adjacent seabed and marine life.

In Miami-Dade, that’s why new levees must have a pile of rock — known as rip rap — at their base. In some places, rocks are piled high enough to stick out of the water, and mangroves and other coastal plants will take root there.

This is what inspired a group of UM scientists to design a rockfill replacement, designed with mangroves and other plants in mind. They call it SEAHIVE, a reference to the six-sided tubes that stack together to look like a beehive honeycomb.

“Think of it as an airbag. It dissipates energy by allowing water to enter it,” said Landolf Rhode-Barbarigos, assistant professor at the University of Miami School of Engineering and leader of the SEAHIVE research team. .

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

The plan is to plant mangroves and corals on SEAHIVE structures in the sunken park so residents – especially children – can swim and experience nature firsthand.

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

Once they’re in place, Rhode-Barbarigos said his team will measure everything from the reaction of fish and plants to how well the structures work to break up the waves. To guard against corrosion and crumbling, they will be constructed with the same plastic polymers as the North Bay Village condominium seawall. If all goes well, he said this technology could be an easy-to-deploy solution for South Florida’s waterfront towns.

“We wanted something robust, easy to implement, easy to manufacture, accessible,” he said. “You can always push the limits of very high technology later. We need the low-tech solution to have sustainable and equitable development.