Storm-Proofing Manhattan — Heaps of Dirt vs. Engineering Know-How.

FDR Drive at East 53rd St. Manhattan, flooded during Hurricane Sandy
FDR Drive at East 53rd St. Manhattan (looking south), flooded during Hurricane Sandy, October 29, 2012. Image: from YouTube by PaulY.

When Hurricane Sandy struck New York City on October 29, 2012, the accompanying 3 meter (10 ft) storm surge flooded about 51 square miles — 17% of the city’s land mass — and caused an estimated $19 billion in physical and economic damage across its five boroughs. Lower Manhattan, with its concentration of high value real estate and underground infrastructure, was particularly hard hit financially. The following map shows the extent of flooding along Lower Manhattan’s shore line.

Map of Lower Manhattan showing areas flooded during Oct 12, 2012 during hurricane Sandy
Areas of Lower Manhattan flooded by hurricane Sandy’s 3 meter storm surge. Image credit: ArcGIS

Despite the multitude of meetings held and reports written on ways to defend Lower Manhattan against future storm surges, nothing has yet been done. A plan, nicknamed ‘The BIG U’, developed by the Bjarke Ingels Group and others, formed the basis for much of the discussions. The plan concerns the low lying areas along Manhattan’s shoreline from West 57th St. down to The Battery, and up to East 42nd St. Discussions focused mainly on where best to build land-based berms and sea walls while, at the same time, preserving shoreline parks and recreational amenities. But earlier this year, Mayor Bill de Blasio announced a plan that departs radically from the BIG U concept. The following excerpt is from a piece by Mayor de Blasio in New York Magazine of March 19 titled My New Plan to Climate-Proof Manhattan:

“South Street Seaport and the Financial District, along the eastern edge of Lower Manhattan, sit so close to sea level — just eight feet above the waterline — and are so crowded with utilities, sewers, and subway lines that we can’t build flood protection on the land. So we’ll have to build more land itself. Over the coming years, we will push out the Lower Manhattan coastline as much as 500 feet, or up to two city blocks, into the East River, from the Brooklyn Bridge to the Battery. The new land will be higher than the current coast, protecting the neighborhoods from future storms and the higher tides that will threaten its survival in the decades to come.”

The following map of Manhattan’s southern tip illustrates the Mayor’s plan, which he says could cost $10 billion. The red line shows the extension of land by 500 ft. from the existing coast.

Map of Lower Manhattan
Mayor Bill de Blasio’s $10 billion plan to extend the Financial District into the East River by up to 500 ft (red line). Red arrow indicates where FDR Dr. becomes an elevated highway heading south. Image: Google Maps

Here’s the mystery:

Why, after five years of discussions about implementing the BIG U, has the Mayor suddenly decided that the only way to save the Financial District is to spend billions dumping dirt offshore? His justification — that the district’s edge is “so crowded with utilities, sewers, and subway lines that we can’t build flood protection on the land” — invites disagreement. First, the city’s tangle of underground infrastructure makes new construction expensive, not impossible. Second, the FDR Drive provides a ready made flood protection line of defense for much of Manhattan’s east side; it’s available to be built on (or under) today — no new land required.

Map of Manhattan - FDR Drive highlighted

The 0.56 mile section of FDR Drive from Old Slip St. in the Financial District  north to the Brooklyn Bridge, and a further 0.7 miles to Mongomery St. in the Lower East Side, consists of elevated roadway that is built above what is now the shore line. North of Mongomery St. the FDR Dr. runs at grade for about 7 miles to East 120th Street. South of Old Slip St. the FDR Dr. becomes the 0.7 mile Battery Park Underpass, which emerges to connect with the south end of West St.

South St. and elevated section of FDR Dr. NYC Financial District.
South St (at Wall St) showing elevated section of FDR Drive in the Financial District (looking North). Parts of East River and Brooklyn Bridge visible at far right. Image: Google

The mayor’s $10 billion land creation scheme would likely take at least 5 years to complete, assuming funds can be raised. The obvious alternative is to fortify the space under the FDR Dr (from Old Slip St. to the Brooklyn Bridge) with a concrete and steel surge barrier (+18 ft high if the vertical space is used to its maximum). Not pretty, but effective. As for Battery Park, there is no technical reason why a berm or sea wall cannot be built on that space from Old Slip St. to the Hudson River side of Manhattan. The cost to protect the Financial District using the combination of land based barriers described above: about $1 billion is my guess. That’s a tenth the cost of the Mayor’s plan. What’s more, the job could be done in a year, if placed on a war footing.

Another departure from the BIG U concept is the city’s new plan for East River Park, the 57 acre, 1.2 mile long strip of land between FDR Dr. and the East River. The original $770 million plan, developed in collaboration with community residents, called for flood walls and berms built alongside the FDR Dr. It was understood that the park itself could flood during a hurricane. The new $1.45 billion plan calls for raising the level of the entire park by 10 feet (requiring about 900,000 cu. yds of fill). The existing park amenities will of course be obliterated in the process. Lorraine Grillo, the city’s Commissioner of Design and Construction, is quoted in the press as saying that the new plan will avoid interfering with traffic on the FDR Drive. Apart from that comment, which puts the interests of motorists ahead of the interests of local residents, there is no apparent justification for the new approach.

Aerial photo of East River Park and Lower Manhattan
Aerial view of East River Park, FDR Driveway, and Lower Manhattan, looking SW. Image: U.S. Gov (FEMA)

A previously considered idea was to cover the FDR Drive by enclosing it in a tunnel (much in the manner used by subterranean termites to protect their above-ground roadways). This would reduce noise and pollution from car traffic, and provide additional green space on the tunnel’s flat roof. The tunnel, fortified on its east side, would act as the surge barrier. It’s time for the city to reconsider the idea before it squanders money on unnecessarily destroying the existing East River Park.

It isn’t easy to plan for potential storm surges. Considering the lack of international action against global warming, the prudent course is to assume that storms will become stronger and that the rate of sea level will continue to speed up. Another superstorm, one even more destructive than Hurricane Sandy, could strike next year. The threat is existential. Therefore, the city’s available flood protection funds should be spent first on structures of concrete and steel such as walls, barriers, bulkheads, that can be built and installed quickly in tight places, and that provide immediate and positive flood protection. In these climate fraught times, the survival of dense maritime cities will depend increasingly on engineering innovation and the technologies involved in building and living on soggy ground, not on piling up ever higher heaps of dirt.

Photo of termite tunnel
Termite tunnel. Image credit: Orkin Co.

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