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How to stop the Big Apple from floating away

Images of the destruction were stark. Seven metro tunnels flooded, Lower Manhattan blacked out for five days, 46 New Yorkers dead and many more injured.

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But what is probably more worrying is that the same thing almost happened a year earlier, when Hurricane Irene’s storm surge was just 50mm short of flooding Lower Manhattan. Faced with those facts, New York State governor Andrew Cuomo commissioned a report on the state’s infrastructure and how it can be protected against future storms and natural disasters.

“We have an enormous harbour and extensive shoreline. After that is the Atlantic Ocean and I don’t think anyone is trying to keep that out”

Michael Bloomberg, Mayor of New York

The NYS2100 Commission’s 205-page report was published last week, with a series of recommendations including a thorough feasibility study into a flood barrier to protect the city (News last week). The report is clear that changes are needed.

“Superstorm Sandy destroyed any lingering perception that the New York Harbour shoreline is sufficiently robust to withstand a storm surge,” it says.

Most experts agree with the report’s recommendation to develop soft infrastructure, such as wetlands and barrier beaches to protect the coastline, but opinion is defi nitely split on hard infrastructure options such as a flood barrier.

Regional Planning Association chairman Bob Yaro - one of the 27 members of the NYS2100 Commission - certainly thinks a barrier is needed and argued the case for a thorough feasibility study in the report. “It’s my belief that it’s the only way of dealing with the storm surge,” he says.

But, despite the devastation caused by Sandy, Yaro acknowledges that a full flood barrier is low on support. “There’s enormous scepticism, particularly amongst the chattering classes,” he says.

New York City mayor Michael Bloomberg is among the prominent figures unconvinced about the practicalities of constructing a barrier. “We have an enormous harbour and extensive shoreline,” said Bloomberg last year. “After that is the Atlantic Ocean and I don’t think anyone is trying to keep that out.”

Bloomberg favours the construction of soft infrastructure that will have a lower impact and much lower costs than a flood barrier. Initial cost estimates for the flood barrier are in the range of $7bn to $29bn (£4.4bn to £18.1bn).

New York would need barriers on the north and south sides of the harbour. The north side barrier would lie between the Bronx and Queens near the Whitestone Bridge. On the south side, barriers would need to be built at the Verrazano Narrows between Staten Island and Brooklyn, and at Perth Amboy between Staten Island and New Jersey, or a much larger barrier would have to be built between Breezy Point on the south western tip of Long Island and Sandy Hook barrier island in New Jersey.

All of these options will be considered by the United States Army Corps of Engineers (USACE), which will be co-ordinating the feasibility study.

The report also acknowledges that existing natural barriers against a storm surge have been slowly eroded. “As shoreline flats were filled and land was expanded, the harbour lost 80% of its historic tidal wetlands and virtually all of the 200,000 acres of historic oyster reefs,” it says.

“Superstorm Sandy destroyed any lingering perception that the New York Harbour shoreline is sufficiently robust to withstand a storm surge”

NYS2100 Commission

“The end result was a commercially accessible waterfront that fuelled the growth of New York City, but one that paradoxically left the city more vulnerable to storms.”

Yaro says removing the natural barriers, along with rising sea levels and more extreme weather events, means only a flood barrier can prevent New York facing similar chaos in the next major storm event.

But will a flood barrier pass the cost benefit analysis test?

Even flood barrier proponents realise sceptics will take some convincing. Mathijs Van Ledden, business development manager at marine infrastructure specialist Royal HaskoningDHV, says New York’s flood risk areas are very different to those protected by the St Petersburg and London barriers. “The nature of flood risk is large areas of low-lying land that could be better protected with smaller natural defences on any cost-benefit analysis; I think there is a long way to go,” he says.

Van Ledden, who is in discussion with USACE about how it will assess the barrier options, says that technically a flood barrier can be built, and would likely require gates to allow for the navigation of shipping traffic. He also welcomed improvements to the soft infrastructure, but warned that it would do little to help if a Sandy-like storm happened again.

The other major question is whether or not New York can afford to build the barrier. There is little information in the commission’s report about how any barrier could be funded, other than a recommendation to establish an infrastructure bank.

Credit Agricole CIB managing director and head of project finance for its global loan syndication group Liam O’Keeffe said a project of this magnitude will need government support. “The big problem for the barrier is that it is too big for banks to fund alone, and the United States has a poor track record in private financing,” he explains.

But Yaro is convinced the money will be found. “We’ve just had a $100bn storm,” he says. “How can a $20bn storm barrier not be cost effective?”

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