These rock outcroppings in Central Park are quiet reminders that at one time – 18,000 years ago – there was over 2,000 feet of solid ice sitting on top of New York. That’s higher than any skyscraper. The stone was etched and polished by glaciers during the last Ice Age. Since so much of the earth’s water was in the form of ice, and that ice was sitting on dry land, the sea level was a few hundred feet lower than it is today. That meant the shoreline was considerably farther out with a lot more exposed territory above water.
And if you go back even further – say 92 million years ago – the Earth was substantially warmer with no ice pack at all and a much higher sea level than today. All of New York City, as well as most the the eastern seaboard, was entirely underwater. In fact, the interior of North America from Texas up through Canada’s prairies was a shallow inland sea.
The climate has changed repeatedly in the past and will do so again in the future. It just happens at a time scale that humans have trouble recognizing. We and our various civilizations just don’t last long enough to experience these long slow cycles directly. It’s a lot to ask someone working within a two or four year election cycle, or a thirty year mortgage, or an eighty year lifespan to take action based on a climate timetable. Hold that thought for a moment…
After Hurricane Sandy flooded low lying portions of New York in October of 2012 the city began to explore ways to protect the built environment from future storm surges. An unusually high tide paired with high winds pushed water into places it hadn’t gone in living memory. Fourteen feet of water doesn’t seem like a terribly high mark, but it’s enough to take down an entire city in a few hours. No one in New York wants to see a repeat of the same kind of flood damage. Talk of a changing climate gets no traction, but when your feet get wet in your living room it grabs your attention.
Bjarke Ingels of BIG proposed a U-shaped storm water barrier that would wrap around the southern tip of Manhattan and double as a series of public amenities rather than a brutal concrete wall that would cut the city off from the waterfront. It’s sometimes called the Dry Line riffing on New York’s High Line.
The High Line was an elevated freight rail line that delivered goods to warehouses in what used to be the meat packing district. Highways largely replaced rail in the 1950s. Suburban refrigerated warehouses replaced the facilities in the city center. The entire neighborhood went into deep decline for decades and the infrastructure and many buildings were left to rot or were torn down.
The reinvention of defunct rail infrastructure as a high quality linear public park was modeled in part by the Promenade Plantée, a similar arrangement in Paris. The addition of this kind of public amenity spurred new investment in surrounding real estate. The more valuable adjacent property became the more the city invested in extending the High Line further along the old surviving rail route. To be clear, no one in the city and very few of the nearby property owners were originally able to see the rusty steel weed covered structure as anything but blight that needed to be demolished. Funny how things work out.
One of the places that helped me understand what the Dry Line might look like (emphasis on might) is Roosevelt Island. Cornell University is currently building a satellite campus there with a comprehensive 500 year flood management design.
The concept is simple. Pedestrian promenades along the water also happen to be fortified embankments. The soil behind them is gently built up in a landscape of rolling berms. (It’s so tempting to call them grassy knolls.) Behind the berms are elevated plazas for casual outdoor dining and recreation. And finally the buildings are placed on water resistant raised platforms. All together the result is a gentle collection of passive techniques for keeping things dry during future floods.
The trouble, of course, is that all this magnificent public space is fantastically expensive. Bjarke Ingels described the Dry Line as a, “barrier with cappuccino.” It’s possible in this context since the larger Cornell campus cost $2B and there will be hotels and Class A offices to rent alongside the university buildings. And that takes us to the next interesting tidbit of urban flood protection.
BIG’s proposal for protecting New York is really a proposal to protect the most valuable real estate in lower Manhattan. The rest of the city that’s vulnerable to floods is evidently out of luck. That includes half of Brooklyn, Queens, Staten Island, the Bronx, and big chunks of New Jersey. If the Dry Line actually gets built does the entire region chip in to pay to save the wealthiest inhabitants of the city? Does the city create a special parcel tax for just the properties served by the Dry Line? Or does the city build the cappuccino versions in some places and plain concrete walls and sand bags in others? Anyone want to guess how things turn out in the South Bronx?
But here’s a more interesting question. How well will the city hold up if its critical infrastructure repeatedly fails to function as storms disrupt normal operations? JFK, LaGuardia, and Newark airports are all an inch and a half above the sea – just like all the sewerage plants. Will they become fortified enclosures that somehow connect to the financial district over miles of soggy neighborhoods? That’s a distinct possibility. Time will tell…