Sandy was predicted to be a large storm, but no one had anticipated the height of the storm surge. Originally predicted to be up to 11 feet, it finally crested at 13.88 feet in Battery Park in Lower Manhattan. That's over three feet above the previous record, set in 1960. Since then, the water level in New York Harborhas risen four to six inches, meaning the city will likely have to endure similarly threatening surges in the coming years.
Though the word "surge" evokes a tsunami-like wall of water, storm surges are comparatively calm events. As hurricane winds whip over the surface of the ocean, they pile up water on the leeward side of the storm. A surge is essentially a bulge of water that slowly creeps above normal levels, similar to flooding on a river like the Mississippi. Storm surges may lack the brutal physicality of a tsunami, but their destructive power shouldn't be underestimated.
Much of New York City is built right up to the water's edge, making it especially vulnerable to storm surges. New Yorkers are coming to grips with this, and, as a result, are starting to ponder how best to adapt the city to the new reality. Proposals run the gamut from quick and dirty—inflatable plugs to seal off subway tunnels—to expensive and permanent—a massive storm barrier that will cost billions of dollars.
Perhaps the most captivating proposal is a storm surge barrier, like the sort Malcolm Bowman advocates. "What I've been proposing over the last five, six years is a barrier system like they have in Europe," says Bowman, a professor of physical oceanography at SUNY Stony Brook. "If it was in place, there would be no damage now within the harbor proper."
Bowman's system would consist of earthen barriers separating the New York Harbor from the Atlantic Ocean, interrupted at intervals by gates that could close in advance of threatening conditions. The majority of the earthwork would span the five mile gap from Sandy Hook in New Jersey to Breezy Point in Brooklyn. Running along the top would be rail lines and a highway.
Barriers for New York Harbor have been proposed in the past, but Sandy has breathed new life into the idea. New York City wouldn't be the first to consider such a vast project. New Orleans is a city surrounded by extensive levees, and though they famously failed after Hurricane Katrina in 2005, they have been rebuilt since and this year during Hurricane Isaac passed their first major test. London has the Thames Barrier, which was completed in the 1980s but was planned after a surge flooded the city in 1953. The Netherlands started planning their defense against the North Sea after that same storm. Called the Delta Works, it is a collection of dikes, dams, and barriers, each of which would be considered a large undertaking on its own. The system took nearly 50 years to complete and separates hundreds of square kilometers of water from the ocean.
By all accounts, the Delta Works' barriers have been successful. So, too, has the Thames Barrier. But no one knows whether they'll stand the test of time. Despite being built to last hundreds of years, not all of the Delta Works' barriers were built to accommodate sea level rise caused by climate change. The same is true of the Thames Barrier, which will need to be upgraded and supplemented over the coming decades in order to cope. As for New Orleans, the new system has held up so far, but there are thousands of people who live outside the walls. They still get flooded.
Which is to say that while manmade barriers are useful—and sometimes indispensable—tools for dealing with storm surges, they aren't the whole answer. "It's really about hybrid solutions, it seems to me," says Denise Reed, a professor of earth and environmental sciences at the University of New Orleans. "It's really about using some of the characteristics of the natural environment to contribute towards risk reduction."
Kate Orff feels the same way. Two years ago, Orff, a landscape architect and assistant professor at Columbia University, proposed rehabilitating New York Harbor's once-extensive oyster beds. Called "Oyster-tecture," her plan was part of an exhibition on rising sea levels at New York's Museum of Modern Art. "I was interested in the idea of scaling as a strategy," Orff says. She was drawn to the idea of using a small organism on a wide scale—"the oyster as a unit of change," as she puts it—rather than relying solely on a monolithic structure. Individually, each oyster may not make much of a difference, but collectively, they might. The beauty of her plan, she says, is "you could start now and begin to build over time."
Reed agrees. "Why not do it?" she says of Orff's Oyster-tecture and other such proposals. "They're what you might call 'no regrets' actions. They don't necessarily cost us a lot of money, they might help a little bit, and there are other benefits out of them, so then why not?"
Given that a storm surge barrier could take 15 years or more to complete, New York City will need other ways to cope with surges in the meantime. Oyster reefs could be one of many adaptations, including trap doors on tunnel openings, elevated subway station entrances, and roof-mounted back-up generators.
But just as storm barriers aren't a complete solution, neither are oyster reefs. "Are oysters enough?" Orff says. "No. Is a storm barrier enough? No. Are making trap doors to our tunnels enough? No."
That's in part because we've built many of our cities right up the the water's edge, where they are most vulnerable. We've filled wetlands that had historically acted as mops during storm surges. We've placed important pieces of infrastructure under sea level. And we're changing the climate in a way that's causing the sea level to rise, which compounds all of the problems listed above.
In the past, people adapted to storm surges by, for example, moving to higher ground or placing their houses on stilts, as Reed and her neighbors southwest of New Orleans have done. But those adaptations are unrealistic for a city of more than 8 million people, especially one built so closely to the water's edge. "New York Harbor, if you add it all up, is 520 miles of coastline," Bowman says. "A great amount of it is bulkheaded. In other words, it's docks, piers, vertical walls." In other words, it would be difficult and expensive to modify such a shoreline to deal with storm surges.
"There will never be a year 15 if there is never a year one."
"I think the idea of multiple lines of defense is something that should be introduced into the conversation in New York," Reed says. That means a storm barrier, oyster beds, restored wetlands, elevated entrances at subway stations, tunnel plugs, and so on.
Figuring out how to pay for all that will be a challenge, as will determining the proper balance between small adaptations, rehabilitated natural defenses, and large constructed works like a storm barrier. But we need to answer those questions soon, Reed says. "It might take 15 years to study, plan, design a major structure, but there will never be a year 15 if there is never a year one."
"It's going to be expensive to build anything like this, and it's also going to take a long time," she adds. "But we have to really think of the cost of the construction, of whatever we want to do, in relation to the damage that occurs if we don't do it."