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October 24, 2014updated 20 Jul 2021 3:06pm

Manhattan’s trying to stop itself from going underwater by extending 500 feet into the East river

By Barbara Speed

On 29 October 2012, a storm surge from Hurricane Sandy hit New York City, and flooded streets, tunnels and subway lines. The power went out. A building collapsed in Chelsea. A carousel along the Brooklyn waterfront was semi-submerged, leaving horses hovering eerily just above the waterline.

City officials had previously estimated that floods severe enough to have a 1 per cent chance of occurring in a given year would cover about 33 square miles of the city. But Sandy covered 51 miles, or 17 per cent of NYC’s total land mass. In Brooklyn, an area double the size of the supposed-floodplain was waterlogged.  And the situation looks set to get worse: the New York City Panel on Climate Change estimates that New York City’s sea levels will rise by up to 75 inches by the 2100s.

So, with the appropriate amount of umming, ahhing and bureaucracy, the municipal government has decided to do something about it. In Staten Island, they’re doing clever things with oysters. Mostly, however, action so far has taken the form of several long reports and a list of 257 proposed measures to flood proof the city.

But one of those reports – pithily titled the “Southern Manhattan coastal protection study: evaluating the feasibility of a multi-purpose levee” and authored by the New York City Economic Development Corporation (NYCEDC) – proposes a plan that would actually be quite dramatic: a new “multi-purpose levee”, to be built along the Lower East Side.

What that means in layman’s terms is that they are planning to build a new bit of land on the Southeastern edge of Manhattan, spanning 1.3 miles from the Manhattan Bridge down to just shy of Manhattan’s southern tip. As to its width, the report suggests several different options for the levee’s width. Under some versions of the plan, it’d be 250 feet wide; the more dramatic version would see the city expanding 500 feet into the river.

The yellow area shows the maximum area the levee would cover:

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Most levees are like huge sea walls, with steep edges to keep out flooding, but the one proposed for New York would have a very gradual slope up from the river’s edge so residential or commercial buildings could be built on top of it.

The report says the new development would fit seamlessly into the city’s existing transport grid. If the plans for a 500 foot levee are carried out, it’d would offer two extra blocks of city streets plus an open space at the water’s edge.

The report concludes that the development would be “financially, legally and technically feasible”. Which is quite impressive when you consider that they’re talking about creating a new bit of city 500 feet by 1.3 miles, at a cost of $3.6bn.

The NYCEDC has a cunning plan to overcome these obstacles: the land infill and infrastructure would be part-funded by a “master developer”, and developers would commit to buying up the new land once it’s built and constructing new buildings. By this reckoning, they believe the levee could actually net the city $700m, as the project could bring in $4.3bn in land sales and taxes.

What this means is that the most dramatic option is actually the only one which could leave the city government in the black, as it offers by the most in terms of revenue.  NYCEDC conclude that the plan to extend by 500 feet would “likely have the most significant impact on community and economic vitality of Southern Manhattan”.

This all sounds pretty exciting: we’d all like a bigger Big Apple. But even if the plan goes ahead, it won’t be finished anytime soon. NYCEDC predicts that for the 500 foot development, the first section of landfill and flood protection could be finished 1 to 5 years after the project gets the go-ahead. Some sections, though, would take half a century. The first buildings on the levee would be completed a 22 years after the project’s start; the last would be finished about 40 years later.

The report’s authors looked at similar examples in Japan and the Netherlands when working out the New York project’s feasibility, but it also looked at examples closer to home: Manhattan’s shoreline has been routinely extended as the city grew, most recently in the form of Battery Park.

Unfortunately for the city’s flood defences, these previous expansions  weren’t brilliantly thought through (perhaps 73-page reports weren’t so fashionable back then). According to the report, they were carried out through “a cycle of building shipping piers, then filling in the land between them and extending new piers further into the water.” These areas were built to be accessible from the river – making them low-lying and, of course, at risk of flooding. It’s these earlier expansions which have made flood protection measures so necessary today.

This 1776 map of Manhattan shows its original, relatively puny size: 

Who knows, maybe by 2500 there won’t be a river at all.  

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