January 30, 2013 - "From Salt Marshes to Sea Barriers, Preparing for the Next Sandy Defense"
Duration: 5 minutes 38 seconds
SBU investigator Malcolm Bowman begins speaking at approximately 3 minutes 51 seconds into the broadcast
Jamaica Bay, a 40-square mile bird sanctuary in southern Brooklyn and Queens, is a testing ground for some of the soft edge approaches being discussed by politicians, planners and environmentalists as future protections against another Sandy.
Dunes line its beaches—or lined them until Sandy came and flattened them and about 180 acres of salt marshes have been restored.
For the most part, officials say these features proved their worth in the storm, although others doubt whether they can be replicated in other parts of the city’s shoreline.
On a recent tour of the bay, Elizabeth Jordan, a landscape architect at the New York City Parks Department, pointed to a low ridge of sand along Plumb Beach. It used to be a line of 12-foot-high sand dunes. Now, that sand is scattered across the bike path, about 50 feet further inland.
Photo caption (at upper left): Lower bay storm surge barrier. NY-NJ Outer Harbor Gateway, Halcrow Group Ltd, UK
“Where other places that don’t have dunes further down, like Rockaway Parkway,” Jordan said, “the actual bike pathway was undermined and we lost part of it because the water wasn’t stopped by dunes.”
The Plumb Beach dunes were constructed by the city and the U.S. Army Corps of Engineers as part of a $6.5 million project just two weeks before Sandy hit. Marit Larson, the director of the wetlands restoration team for the Parks Department, said they did their job.
“If Sandy had happened three weeks before when it did,” she said, “we would have lost the Belt Parkway.”
Jamaica Bay is an odd place to talk about “natural barriers.” It is has been extensively engineered. In the past 150 years, it has at once been made smaller and deeper: channels were dredged so that ships could pass through for a port that was never built; the inlets along its shores have been turned into hard-edged marinas; and much of the dredged sediment was used to raise neighborhoods like Canarsie and Howard Beach out of the marshland and onto terra firma. Plumb Beach as we know it today was actually underwater.
“The whole coastline of Brooklyn and Queens was a series of salt-water marshes, inlets, and different types of sea farming,” Jordan said. “We were the biggest oyster producers in the United States in the 1800s.”
Now, about 300,000 people call the Jamaica Bay environs home and live within 15 feet above sea level. Many of those who lived in the former swamp—in Canarsie, Howard Beach, Gerritsen Beach—got flooded.
Oddly enough, it is engineers who are now in the process of restoring “natural” barriers. Not just the dunes, but the salt marsh too.
Realted YouTube clip ... WNYC: How Can We Save NYC from the Next Sandy? (January 2013)
Video by Jennifer Hsu, WNYC Radio
At the next stop of the tour, Gerritsen Creek, Larson showed off about 20 acres of wetlands that were restored as part of a larger $7.2 million project, also done with the Army Corps. Unlike the dunes along Plumb Beach, the salt marsh survived Sandy well, she said. In fact, the storm “flushed” the stiff reeds of the trash that had built up there.
If protecting the coast were a game of chess, sand dunes would be pawns: cheap, plentiful and easily dispensable. Salt marshes, meanwhile, are more like knights: more resilient, but they also play a specific, limited role.
“It has a very stiff stalk for a grass,” Larson said of salt marsh. “It’s resistant so that it really forms an energy dissipation structure. It attenuates waves as they rise up over it.”
'Not a rosy picture'
But while salt marshes may slow the force of a storm surge, even their advocates admit they do little to actually stop the water. According to one rule of thumb, it takes a mile of wetlands to absorb a foot of storm surge.
For Sandy, which had a 14-foot surge, that means 14 miles—which is about the entire length of Manhattan.
One 1963 study by the U.S. Army Corps of Engineers (click here for more info) arrived at an even more ominous figure: it takes 14 kilometers of wetlands to decrease a storm surge by just one meter (or 2.7 miles for every foot).
"People think that if you add a fringe of wetlands, you can stop a storm surge," said Phil Orton (click here for bio), a research scientist at Stevens Institute of Technology in Hoboken. "And the reality is, it's not a rosy picture."
Still, Orton said that restoring Jamaica Bay to something like it once was is worth it: the bay is large enough, at about 7 miles wide, where it could mitigate surges by at least a few feet. He also said that wetlands restoration will have other benefits, such as protecting wildlife.
“There’s this opportunity with Jamaica Bay to restore a system that’s not really being used for shipping any more,” he said.
Orton has studied the hydodynamics of Jamaica Bay and says the shipping channels may well have intensified Sandy's damage in neighborhoods like Canarsie and Howard Beach.
"They dredged out the entrance channel to Jamaica Bay and made it much deeper and the tides come in a lot stronger, and the high tides are higher," he said.
A $20 Billion Solution
But Jamaica Bay may be just about the only place in New York City where salt marshes could have an impact. Malcolm Bowman, professor of oceanography at Stony Brook University, says most of the city's shoreline drops down too quickly to foster vegetation.
"You’ve got 520 miles of coastline, most of it’s bulk-headed seawalls, wharves, docks ventilation shafts, etc., and there’s very little space to grow anything,” said Malcolm Bowman (click here for bio), professor of oceanography at Stony Brook University.
Bowman is an advocate of what could be called the rook, or maybe the queen, of the coastal chess board: a steel and concrete hurricane barrier. Already in use in London, Rotterdam and St. Petersburg, Russia, these barriers will stop the surge, but they are also very dear to build and maintain.
Bowman has proposed building a barrier that would stretch across the mouth of Lower New York Harbor, between Sandy Hook, N.J., and Breezy Point on the Rockaway Peninsula in Queens. Another barrier would stretch across the very top of the East River in the Bronx to protect the harbor from surges entering from Long Island Sound.
The barriers would have gates to let ships and water pass through during normal weather, then close up for heavy storms. Such a barrier system could cost around $20 billion, though Bowman says it could also generate revenue if a toll road or light rail were constructed on top of it.
Mayor Michael Bloomberg has criticized the barrier, pointing out it wouldn’t protect the Rockaways, which sustained some of the worst damage. New York Governor Andrew Cuomo has also expressed doubts, but has agreed to study it. A spokesman for the U-S Army Corps of Engineers meanwhile, says such a study could take years to complete.
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