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How will New York keep out a rising sea? Dikes, huge sea wall, oyster beds?

After superstorm Sandy, New York officials look for long-term solutions against future floods from storm surges. Many options, little consensus.

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Mr. Yaro points to the Dutch, who keep building higher and higher dikes to keep the North Sea at bay. "They have gone from preparing for the worst storm in 10,000 years to preparing for the worst storm in 100,000 years," he says. "They are also building so they have more redundancy and so they function better with natural systems."

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One proponent of some form of sea wall is Malcolm Bowman of the State University of New York at Stony Brook, who heads the school's group that predicts and models storm surges for the New York area.

Professor Bowman uses as an example the Halcrow Group plan, which involves a long, tall causeway that would be built outside the harbor in water about 20 feet deep. Huge gates would allow ships in and out but would close during powerful storms to keep out the surge. Additional barriers would be built in western Long Island Sound and Arthur Kill, a waterway in Staten Island.

"The barrier could double as an interstate highway, a New York City bypass, and could also have a light-rail system to JFK [international airport]," says Bowman, who estimates the cost for the outer barrier alone could be $10 billion.

With the barrier, he says, the affected water would spread out to other areas, including Long Island and New Jersey, which would see sea levels rise by about an extra six inches during storms. Also, studies would need to determine the barrier's effect on migrating fish.

Architect Stephen Cassell, who participated in the MoMA event, says New York should consider "softer" approaches. Under his plan, the city would install freshwater and saltwater wetlands to absorb some of the energy of a storm surge. The marsh at the tip of Manhattan would look like a green beard surrounding the city.

Barrier islands could be built outside the marshes to act as another way to absorb a storm surge, he says. "That's the nature of a soft infrastructure: You are designing for redundancy," says Mr. Cassell, a principal in the firm Architecture Research Office here.

At the same time he envisions streets that absorb water, allowing large amounts of rain to reach the ground below. The water would flow into underground canals that go back to the harbor and rivers.

The Dutch, Cassell says, are adopting some of these ideas, as well. "They are realizing the hard infrastructure is not the only way to deal with the storms," he says.

Yaro, who favors some sort of storm barrier, says a combination of approaches is necessary. Take oyster beds, which used to fill New York Harbor.

"Oyster beds slow down the wave action, and secondly they help clean up the harbor," he says. "And then you can eat those babies once the harbor is cleaned up."


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