CNN
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By 2025, New York's Staten Island will be fortified by a towering seawall running 5.3 miles along the coast, an engineering feat designed to ward off a growing threat. The climate crisis is predicted to create more powerful and extreme weather systems all over the world, and coastal engineers are racing to respond with structures to reduce their impact. The first seawalls were built centuries ago, though there are now, arguably, greater assets to protect and more people living along vulnerable coastlines than ever before. A recent report by the Center for Climate Integrity estimated it could cost the US more than $400 billion over the next 20 years to protect coastal communities.
"Where you have these public and private interests colliding in a contested space, like the coast, that faces ordinary weather events being compounded by climate change, people will look for a solution that gives them as much security as they can hope to achieve," said Tayanah O'Donnell, a senior lecturer at the Australian National University (ANU).
Seawalls are not only expensive to install but need regular maintenance if they are to withstand the prolonged barrage of pounding waves. But in many places they are considered vital to protect land and property that would otherwise be swept out to sea.
When Hurricane Sandy smashed into the US East Coast in 2012, Staten Island was overwhelmed by massive waves that swept away properties and killed 24 of the dozens of people who eventually died in the storm. With a population of almost half a million, low-lying Staten Island was no match for the waves whipped up in New York Harbor, one of which reached a record 32.5 feet high.
Seven years later, $615 million in funding has been secured for the ultimate defense -- a levee, buried seawall and vertical floodwall reaching 20 feet above sea level. Topped with a public walkway, it's officially being called the "Staten Island Multi-Use Elevated Promenade." Graphic visualizations of the wall, released by New York Governor Andrew Cuomo's office, show happy cyclists riding along a wooden deck near an ice-cream stand and coin-operated telescopes pointed out to sea.
The seawall will be built to withstand a 300-year flood event -- a water height two feet above the highest levels recorded during Hurricane Sandy, said Frank Verga, a project manager at the New York District of the United States Army Corps of Engineers (USACE). "The project is a proven engineering solution to withstand multiple storms, with adaptability to be modified in future to address sea level rise, if required," said Verga in an email.https://edition.cnn.com/style/article/snohetta-underwater-restaurant-construction/index.html
The design of seawalls has evolved over time, from rock -- which is still used -- to interlocking concrete units, including the Tetrapods commonly seen in Japan. When rock isn't available, concrete can be more cost-efficient, allowing large numbers of correctly-sized parts to be produced. In recent years there's been a greater push towards natural solutions -- using dunes, mangroves and man-made reefs alongside man-made walls to help calm the sea. "We're not only building a structure that is functional in an engineering sense but it's functional in an environmental sense," said Matt Eliot, a coastal engineer and direct of Seashore Engineering based in Perth, Australia. "We're using that to look for what habitats we can encourage to make it better for the plants and animals in the area."
More modern designs combine a number of protective features to create sheltered habitats for marine animals and plants. At Fort Pierce Marina in Florida, designers at Tetra Tech built a series of curved breakwater islands and tee-shaped groins to repair some of the damage caused by Hurricane Frances in 2004. The hard engineering is complemented by 21 acres of new habitats for oysters, mangroves, dune grass and seagrass, as well as a nesting ground for birds.
In New York, the first contracts for the Staten Island seawall are expected to be awarded next summer, with work to begin soon after, according to the USACE. The design also includes wetlands, and is part of the New York Mayor Bill de Blasio's $10 billion scheme to "climate-proof" New York City, an investment he says is needed to tackle a "national emergency."
"New York doesn't have a choice but to prepare for what's coming. Neither does Miami, Houston, Charleston or any of the coastal cities facing an existential threat to their future," De Blasio wrote in an article in March for a New York magazine.
And it's not just US cities facing the threat of rising water. Major international cities including Jakarta in Indonesia and Ho Chi Minh in Vietnam -- home to a combined 18 million people -- are under urgent pressure to act. With so many people living so close to the sea, the potential losses are staggering-- and the financial cost of creating a durable solution is rising by the day.
"The longer we take to mitigate against climate change, the more expensive it's going to be to adapt to a changing climate," O'Donnell said.
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