Manhattan Goes Dutch: Guarding Gotham With Levees

Hurricane Sandy has a lot of serious people — including New York's governor — calling for New York City to follow New Orleans

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A woman walks along the 17th Street canal levee wall in New Orleans, Aug. 26, 2010.

There may be no species better at preparing for the last war than humans. We tighten airport security only after a tragedy like 9/11. We invest in better voting machines only after a mess like the 2000 election. Now, as a shocked and sodden New York struggles to recover from Hurricane Sandy, planners are once again considering the idea of protecting the city with sea walls, levees and flood gates — the kind of infrastructure that is at last in place in New Orleans and could have spared Manhattan and the other boroughs much of the recent storm’s damage. In this case, however, the urgency is even greater, since the just-past war is also a foretaste of the ones to come, as Sandy-like storms become the scary new normal.

The scope of the devastation Sandy left in terms of dollar-cost and property lost is hard to overstate — tens of thousands of people displaced and up to $20 billion in property damage. But overlooked in those human and fiscal figures are the truly alarming meteorological ones. Until last week, the highest flood surge ever to hit New York City occurred in 1960, when Hurricane Donna pushed sea water 5.3 ft. (1.6 m) above average low tide. Hurricane Irene, in August 2011, came close, at 4.8 ft. (1.5 m). But only three hurricanes besides Donna have cleared the 5 ft. mark since 1950. Sandy blew the doors off the other storms, cresting at a stunning 9.1 ft. (2.8 m) above low tide.

“Hurricane Sandy demolished the record books,” says climatolologist Ben Strauss, director of sea level studies for the research and advocacy group Climate Central. “It will take a long time for us to understand all of the dimensions of this storm.”

(MORE: The Lessons from New York’s Flooded Subways)

The dimensions of New York City itself are much better known — and they illustrate starkly why a storm like Sandy can do the damage this one did. The city, cut by the Hudson, Harlem and East Rivers and hard against both the Long Island and New York Harbors, has a snaking 520 miles (837 km) of exposed coastline, much of it just a foot or two above sea level. And the juxtaposition of the various waterways makes things more perilous still.

“The two harbors are like funnels pointed at Manhattan,” says Strauss. “They’re connected by the East River, and when a storm surge pushes in, the river overflows its banks. That’s why the lower east side [of Manhattan] was hurt so badly by Sandy.”

You’d think a city like New York would have been designed around such risks. Its earliest founders, after all, were the Dutch, who know a thing or two about building dikes, levees and sea walls. But Manhattan in the 17th century wasn’t like the Low Countries in Europe, because the ocean along the Atlantic coast was stable and predictable. Those couple of feet the city sits above sea level were enough. Not any more. “Sandy started from a one-ft. (.3 m) higher sea level than it would have a century ago,” says Strauss. “By the end of the century, we could easily see four additional ft. of sea-level rise around New York City. And that’s in the mid-range of projections.”

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The cause, of course, is climate change and ice melt, but for all the urgent talk about how we need to get that problem under control — and we do — a certain amount of additional warming and sea-level rise is now baked into the system. We can slow and ultimately reverse things over the course of many generations, but we can’t call back the greenhouse emissions that are already in the atmosphere or simply turn the switch off of the additional gasses we add every day. That means we have to prepare for the worsening environmental conditions that are sure to come.

In 2002, a research group at the State University of New York, Stony Brook, working with the state’s Environmental Protection Agency, to put together a plan for protecting the five boroughs of the city and the greater metropolitan area from storm surges. Such an undertaking, they concluded in a report they released two years later, would be neither easy nor cheap. It would rely on a mix of sea walls and levees, as well as three massive flood gates at the East River and near the Throgs Neck and Verrazano Narrows Bridges. They would all have to be supported by a finer infrastructure of pumps, piping, hydraulics and electrical systems, with the total project costing an estimated $10 billion — before the inevitable delays and cost overruns.

None of this is technically or financially out of reach. “Lots of cities have done this,” says Kate Ascher, a professor at Columbia University’s graduate school of architecture and planning and author of The Works: Anatomy of a City. “The funding, of course, is a huge issue because it would cost a ton. But you’re protecting assets that would be invaluable.”

But human — to say nothing of bureaucratic — nature being what it is, nothing came of the 2004 plan. That remained true even after Hurricane Katrina in 2005 and Irene last year. Now, however, Sandy has caused the Stony Brook proposal to get another look. In a radio interview after the storm, New York Gov. Andrew Cuomo called for serious consideration of  the levee system — and sooner rather than later. “The construction of this city did not anticipate these kinds of situations,” he said. “As soon as you breach the sides of Manhattan you now have a whole infrastructure under the city that fills — the subway system, the foundations for buildings.”

(MORE: Hurricane Sandy Will Put a Rickety Power Grid to the Test)

Hurricane Sandy may even help lower the cost of construction, if only by making it easier for designers to determine which areas of the city need the most coverage and which can get by with less. “A lot of Manhattan is not nearly as vulnerable as the area that flooded,” says Ascher. “In some ways this was a great exercise to show us where we’re vulnerable.”

But building a levee system means building it all the way, since any corner-cutting or partial implementation may only make things worse. Hoboken, N.J., for example, is protected by levees at its north and south ends, which is great, but only until those walls get overtopped by water. Without the necessary pumps and other infrastructure, standing water gets trapped inside. “You get a kind of lake,” Strauss says. “You saw this in New Orleans too.”

Manhattan, in many ways, is better equipped to handle rising sea levels than a lot of other coastal areas like Florida. While much of its waterfront is artificial, built on relatively porous landfill, the bulk of the island is made up of solid granite. As long as you keep the storm surges out, you don’t have to worry about the damage that the slow seep of higher, warmer sea water can do. Florida, built on spongy limestone, is at risk of crumbling away even if there were never another hurricane.

Hurricanes, of course, are not going away. Strauss now projects one Sandy-type storm every 15 years by the end of the century. That is the proximate result of the reckless way we’ve handled our environment. The very least we can do, as we slowly correct our self-made climate problem, is manage our infrastructure with more care.

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