Flood-proofing New York City with storm barriers

in Queens — would give additional protection (this was the idea proposed by the Halcrow Group’s engineers). Halcrow described the estimated $5.9 billion project at a March conference at New York University’s Polytechnic Institute; three other firms aired conceptual designs for pieces of the estimated $9.1 billion three-barrier network.

All would have gates, navigation locks, or other mechanisms to let water and boat traffic flow under normal conditions — but block a 25-foot storm surge when needed. Some would have substantial walls or berms visible all the time, but one concept, from New York-based Parsons Brinckerhoff, is a wall that would lie flat and virtually invisible on the bed of the East River, pivoting up when needed. The wall would jut out of the water at an angle to block storm surges.

Deputy emergency management commissioner Kelly McKinney said the barriers were as yet too theoretical for the city to analyze but “an intriguing idea.”

If (experts) came back with more concrete details and costs and things like that, we’d be interested” in exploring it further, he said. Meanwhile, the city is taking smaller steps to prepare for potential flooding, such as moving critical pumps to higher spots in wastewater treatment plants.

Engineers say the barriers are technically feasible, but questions remain about their environmental and political viability. Structures that constrict the flow of water could alter fish migration, shellfishing beds and the salinity in the harbor, said Robert “Larry” Swanson, a Stony Brook University oceanographer. Bigger problems could lie outside the barriers. No one has suggested yet how to pay for them, but a sizable public investment could be hard to sell to a city that would be only partly protected - let alone to a federal government that might then face similar requests from other vulnerable communities.

At least one scientist questions whether the barriers would be the best choice even for those inside. Given the unknowns of climate change, any system designed now could prove inadequate in the future, said Klaus Jacob, a Columbia University climate-risk researcher. Some scientists say London’s Thames Barrier, finished twenty-six years ago, may not be able to keep up with rising tides.

If New Yorkers relied on a barrier system, they might be forced to raise it indefinitely — or, worse, unable to do so, Jacob fears. New Yorkers could instead prepare to “live with the water, rather than fight it,” he said, by taking such steps as making tunnel entrances sealable and moving buildings’ electrical and other vital equipment from basements to higher floors.

Hill and Bowman are skeptical that such measures can do enough, but for now, their goal is a full-fledged study of the barriers and possible alternatives - work they say can’t afford to wait. “We’re going to have to do something,” Bowman said. “Or else you retreat, and that’s inconceivable. How are you going to retreat from New York City?”