New York City urgently needs a flood barrier to protect it against further flooding and rising sea levels, leading engineers said this week.
Cornell University School of Civil and Environmental Engineering professor Tom O’Rourke led the calls for New York to beef up its flood defences.
Subway operator Metropolitan Transit Authority added its voice to the call, saying that greater protection for the city’s transport system was needed.
O’Rourke led the analysis of the impact of the 9/11 attacks on Manhattan and assessed critical infrastructure in New Orleans following Hurricane Katrina.
Earlier this month Hurricane Sandy’s 4m tidal surge wreaked havoc on the New York region (News last week).
“New York City has got to come to terms with it [increased flood risk],” said O’Rourke. “It’s no longer a possibility but a probability.”
“Hurricane Irene [last year] was a near miss,” he added. “You cannot say [the flooding] was a rare event when it happens two years in a row.”
Although O’Rourke agreed that Hurricane Sandy was not as “complete” a disaster as the impact of Katrina on New Orleans, he still urged city officials to take the issue seriously.
“It has to be part of the city’s commitments,” added O’Rourke. “It cannot afford the consequences if not.”
But New York City mayor Michael Bloomberg has repeatedly ruled out a storm barrier.
“We have an enormous harbour and an extensive shoreline,” said Bloomberg at a press conference last week.
“After that it is the Atlantic Ocean and I don’t think anyone is trying to keep that out.”
But New York State University physical oceanography professor Malcolm Bowman has been campaigning for many years to highlight the risks that rising sealevels, and tidal surges bring to New York City.
“I’ve been trying for years to get them [the New York City authorities] interested in barriers but they have not been interested,” said Bowman.
Bowman said he organised a seminar in 2009 predicting a Hurricane Sandy type event and that the New York City authorities sent just one junior engineer.
“I felt like a prophet crying in the wilderness,” added Bowman.
But Bowman was encouraged last week by New York state governor Andrew Cuomo’s positive comments about looking into a barrier.
“There needs to be a regional approach,” said Bowman, explaining that it was too big an issue for the city administration to deal with alone.
Bowman believes New York City would need two separate flood barriers. The largest would be between Breezy Point on the south western tip of Long Island in New York and Sandy Hook barrier island in New Jersey. A second barrier would be required to the north east of the city between Bronx and Queens near the Whitestone Bridge.
“The big question is will it be cost-effective.”
The outlay would be astronomical - with initial estimates putting the cost of both barriers at around $15bn (£9.4bn).
The largest barrier - between Long Island and New Jersey - would be about 8km long, according to Bowman.
“But the water is shallow - between 7m to 8m,” he added.
A shorter barrier across The Narrows between Staten Island and Brooklyn has been considered in the past, but experts believe the channel is too deep and the water too fast flowing to make construction practical. The seabed is up to 43m below sea level at this point, meaning the barrier would need to be at least 50m tall to offer flood protection.
“It is just too deep,” said Bowman, adding that a barrier in this location would also not protect Staten Island, which was badly hit by Sandy.
Marine expert Royal Haskoning DHV business development manager Mathijs van Ledden said the longer barrier is technically possible to build.
“It should be feasible,” said van Ledden. “The big question is will it be cost-effective.”
Van Ledden said the substructure below New York is well suited for construction as there is rock just below the sea bed. Van Ledden acknowledged any system would have to have lock gates - similar to the design used in St Petersburg in Russia - for the large amount of shipping traffic.
He also acknowledged potential drawbacks. Water quality in the Upper Bay could be affected and there could be localised coastal erosion.
Any construction within the waters around New York would be commissioned by the US Army Corps of Engineers under the guidance of the Federal government, said Bowman.
He added the protection was desperately needed.
“The water levels are rising 1 inch [25.4mm] every decade,” said Bowman. “That is a fact.”
“Any future tidal surge will be on top of that rising sea level.”