"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."