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New York City commuters have gotten used to bizarre delays. Falling tree limbs and trains that were invisible to controllers until a computer was rebooted are among the issues that have slowed down commutes. But visitors to Williamsburg’s Broadway station were recently met with an obstacle they couldn’t get around: a Kevlar cover over the entrance topped with several feet of water.

The artificial flood, it turned out, was a test of a Flex-Gate, just one piece of a massive effort by the New York state-run Metropolitan Transportation Authority (MTA) to defend the city’s subways from climate change-fueled storms. More than seven years after Superstorm Sandy made a beeline for the city and dumped hundreds of millions of gallons of water into its subway tunnels and caused billions of dollars in damage, New York is on a mission to see that it doesn’t happen again. The transit agency has spent years building and installing and testing an arsenal of custom-designed gates, doors, and assorted covers. The defenses are all but ready, but the true test won’t come until New York comes face-to-face with its next storm.


New York’s subway system has enabled the city’s spectacular growth. Its population more than doubled in the first 30 years after the first subway tunnels opened, largely by the development of land previously considered too distant for commuting. But the same subway is now the city’s Achilles heel in an age of sea level rise. Unlike Miami, which could be inundated entirely by the end of the century, much of New York sits on high ground. Unfortunately, that may not matter if there’s no longer a way to get around the city because the transit system keeps filling with water.

Even on a clear day, 13 million gallons of water must be pumped out to counter incursions from underground springs and other parts of the groundwater system that the subway tunnels were bored through. But Sandy made it clear the subway system is a drainage ditch waiting to happen. With most of the system underground, all it takes is a handful of access points for floodwater to pour in unabated.

During Sandy, only the quick thinking of some MTA engineers who raced into tunnels to relocate irreplaceable signaling equipment in the hours before the storm saved the city from an even worse transit disaster, Columbia University climatologist Klaus Jacob noted. As it was, much of the subway system was shut down for a week, and some lines are still facing service disruptions today to accommodate repairs of damage dating back to Sandy.

The problem with making the 245-mile subway system watertight is that there are an awful lot of ways for water to get in. Subway entrances are the relatively easy part to seal because there are only a handful per station. “Relative” in this sense has meant using technology designed for space missions to create the Flex-Gates. Currently, 64 of a planned 68 have been installed at 21 separate subway stations.

Far trickier are the thousands of ventilation grates that pepper city streets along subway lines. A novel engineering design when they were designed in the early 20th century to avoid the need for exhaust fans by allowing passing trains to draw fresh air into tunnels by differential air pressure as they zoom past, they’re now a massive sieve through which stormwater can pour into the system during a storm. In 2016, the MTA reported that it had identified 5,600 potential access points for water in Lower Manhattan alone, with thousands more scattered across the city.

Jacob, the scientist who in 2011 first predicted that the subways could face a flooding disaster from future storms (he has since consulted with the MTA on its flood prevention plans), is largely impressed by the job the authority has done. It’s used National Oceanic and Atmospheric Administration flood maps to project which parts of the city would be inundated by a 16-foot storm surge (three feet more than Sandy) on top of three feet of sea level rise (a level that could be reached as soon as 2050 at current rates of accelerating warming). The agency has also identified thousands of locations where water could enter the subway system, “from entrances to shafts to sidewalk grates to you name it, even manholes,” Jacob told Earther. And now it’s trying to plug those holes.

An MTA press release from the seventh anniversary of Sandy this October reported that about 3,500 “points of water entry” had received flood protection devices, including “24 doors similar to those used on submarines, each weighing 3,000 pounds; 2,300 waterproof gates deployed underneath sidewalk grates for station vents; 1,700 portable vent covers; and 68 flexible stairwell covers that can withstand up to 14 feet of water.”

The multiple designs—12 different ones, by Jacob’s count—have evolved over the years. An earlier effort to install self-deploying flip gates under ventilation grates that would slam closed in response to the weight of incoming water (and which Jacob and others had warned could become easily clogged by leaves or litter) have been swapped out for metal doors that must be lowered by hand. For vents where this isn’t an option, the MTA told Earther, it has invested in weighed fiberglass boards fitted with gaskets that will create a seal that should stave off floodwaters.

“If those devices perform as they were designed, then the MTA is in really good shape, out to roughly the year 2050 for Category 2 storms,” said Jacob. But he noted that’s a big “if” when you’re talking about an untested collection of engineering solutions being deployed against a 300-quadrillion-ton ocean roiled by Anthropocene-level storms.

“The reality is you must expect some failures—that’s part of engineering,” Jacob said.

The MTA has indicated that it has prepared three temporary walls that can be installed within key tunnels to provide redundant protection for especially low-lying sections of the system. Jacob said he would also prefer to see more redundancy measures so that the subways are still protected even if one set of gaskets fail. But those, he admitted, are “quite expensive and difficult to implement,” especially since they’d likely have to be put in place in the tunnels themselves, which are busy with trains running 24 hours a day.

There’s also the question of how long it will take for transit officials to deploy all of these gates, doors, and floodwalls as a storm approaches. The MTA indicated that all of its new flood-control measures are designed to be deployable in about an hour, including even temporary tunnel walls that must be fitted slat-to-groove by hand. But that assumes that MTA staff are already in place at each of the sites. Getting workers to 2,300 sites to turn a key to lower sidewalk grate covers will take time. And time will be of the essence in defending against future storms. (Asked about its available staff or how long it would take for them to move into place, the MTA replied only that this would “vary depending upon the severity of storm.”)

While shutting down a subway system a day or two in advance seems a small price to pay for saving billions of dollars in repairs, it’s worth remembering that even a couple of days before Sandy made landfall, forecasters were uncertain whether the storm would slam into the Eastern seaboard or drift harmlessly out to sea. In a city where public outrage over government inaction is only rivaled by outrage over action that turns out to inconvenience people unnecessarily, state and city officials will likely be under pressure to avoid shutting down the subway before they’re certain a storm will hit, while not waiting until its too late to put all the protections in place.

Ultimately, New Yorkers won’t know whether the MTA’s ongoing efforts to waterproof the subways are a winning strategy until the next big storm hits. That could be as soon as next year or not for a generation or more, though the odds of intense storms increase every year we continue cranking up the heat in the atmosphere and oceans. And when a storm inevitably hits, Jacob said it could only take a single breach to create another Sandy-like disaster. He pointed to some “critical entrances” to the system along Canal Street, the lower Manhattan thoroughfare named for a long-ago waterway that still follows its near-sea-level course across the entire width of the borough. The MTA has installed the most flood prevention measures, if only because it’s the section of the subway system with the most holes.

“If they were to fail or not perform as designed, then the other 3,000-plus measures are good for nothing,” Jacob said.

That water-covered Flex-Gate that greeted New York commuters, then, should come as a reassuring sign that the MTA is at work to ward off transit disaster during future storms. But the defense of the subways could ultimately hang on more mundane items like a rubber gasket.

“It’s the weakest link in the chain that really determines the fate of the whole system,” Jacob said.

Neil deMause has covered transit and climate issues for the Village Voice, City Limits, Gothamist, and other publications. He lives in Brooklyn, in an apartment at a high enough elevation to be outside the city’s designated flood zones (he checked before moving in).

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