News
03.12.2013
Going Dutch
New draft report suggests ways to protect against rising tides in New York City.
The Oosterscheldekering, a storm surge barrier in the Netherlands.
vtveen / Flickr

Shoot-from-the-hip statements by politicians and what appear to be radically opposing solutions from experts have only added to the confusion over how best to prepare for the next hurricane. Certainly, the most controversial flood-protection debate in Hurricane Sandy’s aftermath is the question of whether New York City needs floodgates.

To help clarify what the different scenarios involve, a 72-page draft report titled “Cost Estimates for Storm Surge Barriers and Flood Protection in New York City” has just been completed by several academics in Holland, along with Malcolm Bowman, a professor of oceanography at Stony Brook University and a member of the New York City Panel on Climate Change.

The draft surge-barrier report provides detailed estimated costs of three different floodgate scenarios, as well as additional waterproofing measures and levee systems that will be necessary whether or not the city decides that floodgates are actually required. Jeroen Aerts, a professor of environmental studies at the Free University of Amsterdam, and one of the report’s authors, said it will stimulate a more informed discussion.

“Right now in the media, they act like there are only two options,” Aerts said, “but we can start on the ‘no regret measures’ and study the big barriers for later.”

The report lays out three different plans for floodgates. One, called “Environmental Dynamics,” would close off New York City’s waterways at the Arthur Kill, the Verrazano Narrows, and the East River. Based on historical analysis, the plan is projected to cost $7.5 billion to $10.5 billion to build, and $77.5 million in annual maintenance costs. An additional gate, to protect Jamaica Bay, would add $4.1 billion to $6.1 billion to the costs of this option.

A two-gate option, “NY-NJ Connects,” would seal the city’s harbor with one gate across the East River and another running from Breezy Point to Sandy Hook. This plan would cost an estimated $7.3 billion to $10.1 billion to build and another $104 million in annual maintenance costs.

In addition to the expense, a major concern about floodgates is their environmental impact. Aerts said that a two-gate solution would be the simplest and most inexpensive to build and maintain. However, the water displacement of such a system could change the ecology of the Hudson River’s estuary and cause environmental damage to the Jamaica Wildlife Refuge, one of the largest and most productive eco-systems in the northeastern United States.

The report also describes 10 different types of flood protection measures to augment floodgates. Several involve fixing or replacing existing manmade infrastructure. One consideration here would be the bulkheads around the city originally designed to prevent soil erosion but in poor condition today since many are more than 50 years old. Another such “soft” measure would fix the harbor’s natural flood protection systems by ramping up wetland and salt marsh restoration in places such as Jamaica Bay, to help protect the bay’s surrounding homes from hurricanes and erosion.

Some of the suggested measures also could dramatically change the appearance of the metropolitan region’s coastlines. Seven-foot-high to 30-foot-high reinforced concrete walls with steel cut-offs could be deployed in outer-lying areas. Armored dikes with woven textiles and steel-sheet piles for support are also proposed. Along coastal stretches and the FDR Drive, the report suggests the possibility of returning to the days of elevated highways, raised on embankments or stilts.

Of course, spoiling the majestic views in places like Lower Manhattan with unsightly floodwalls and dikes would be unacceptable. Accordingly, the report suggests elevating and changing the grade of parkland in places such as Battery Park City. Another “no regret” strategy, which could be employed in the Rockaways, for example, would hide dikes inside dunes augmented with extra sand.

Although the surge-barrier report explores many different protection strategies, one that is not addressed is the “retreat” option, whereby communities would be resettled from flood-prone areas. “Retreat is not an option, but what we can do is build more resiliently,” declared Aerts. “Coastal cities remain attractive, and the only option we have is to protect ourselves.”

Alex Ulam