Shelter from the Storm

Now: The current appearance of the East River waterfront, just south of the Brooklyn Bridge, with no flood protections in place

The administration of Mayor Bill de Blasio is formulating short-term strategies to protect the South Street Seaport and the Financial District from sea-level rise and future extreme-weather events.

These “interim flood protection measures” (or IFPMs) are intended to serve as placeholders, while City Hall embarks on the decade-long process of planning to extend the Lower Manhattan shoreline by several hundred feet into the East River, in order to create a permanent barrier that will hold back the deluge from disasters related to global warming.

Soon: A rendering of the same location, after Hesco barriers have been set in place, providing partial protection against rising waters.

These interim measures were the topic of discussion at the April 26 meting of Community Board 1 (CB1), in which Alice Blank (who chairs that panel’s Environmental Protection Committee) explained, “one of the strategies being used by the Mayor’s Office of Resiliency to address resiliency concerns Downtown is Hesco barriers.” These are a combination of heavy duty fabric liners with collapsible wire mesh containers, which are filled with sand, soil or gravel. They can be installed relatively quickly, stacked or placed side by side, and left in place for years at a time. “These are four-by-four foot concrete barriers that would stay in place for about five years,” Ms. Blank observed.

Later: An illustration of this site during storm conditions, after tiger dams have been deployed to supplement the Hesco barriers.

Also being considered, Ms. Blank noted, “are tiger dams” — cylindrical rubber bladders that are inflated with water, forming an immobile barrier that can contain flooding. “The City held a deployment exercise last June for tiger dams,” she recounted. “This showed that it takes about an hour to put up 50 feet of barriers. And people have to be trained to do it. So it’s an expensive proposition. But it’s doable.”

Finally, she noted, a third set of anti-flood devices being considered by the Office of Resiliency is flood panels, which are rigid barriers placed in front of especially critical facilities, like government offices.

Ms. Blank added that the City’s Office of Emergency Management is also considering a beautification initiative, “to decorate these structures and make them more palatable.”

Someday: Aqua Fences being tested at One World Trade Center.

She also acknowledged that, “the unpleasant look of Hesco barriers and cost and time needed for tiger dams has led the City to look at another strategy: aqua fences.” These are foldable, interlocking panels that flip upward as a torrent approaches, using the weight of the oncoming water to hold back the flood. This system has been tested at several Lower Manhattan buildings, such as One World Trade Center, 17 State Street, 80 Pine Street, and Two Water Street.

While any of these measures could theoretically provide at least partial protection against a future surge of water from the East River, a briefing book prepared by the Mayor’s Office of Resiliency warns that IFPMs do not protect against severe storms like 2012’s Hurricane Sandy, offer any relief from flooding caused by rainfall, or provide security against Nor’Easter storms, “due to current limitations in forecasting timelines and confidence.”