Saving New York's Subway from Sandy

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The water just kept flowing. It streamed through the streets of lower Manhattan, pouring into subway entrances, cascading into ventilation grates and pooling inside tunnels.

Hurricane season is here, and for active storm seasons that means hearing the names of many systems whipping their way across the world's oceans.
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When Superstorm Sandy hit New York a year ago, it caused a massive, 14-foot storm surge, the likes of which the city had never seen. Nine out of the 14 subway tunnels beneath rivers around the city flooded, and the subway was shut down for days. But the Metropolitan Transit Authority (MTA) took precautions to head off the worst impacts, experts say.

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Before the storm hit, the MTA moved its trains out of flood-prone areas and took out the electric signals in the tunnels. The tunnels flooded. Afterward, subway workers pumped the water out and replaced the electric signals. Within a week, 80 percent of subway service had been restored, newspapers reported. (On the Ground: Hurricane Sandy in Images)

The MTA's preparations saved the city significant time and money in getting the system up and running again, said Klaus Jacob, a climate scientist at the Lamont Doherty Earth Observatory at Columbia University in New York, one of the people perhaps most responsible for showing how such epic flooding would affect the city's subways.

"Instead of the one to 10 days that much of the system was down, it would have been down at least three weeks, which saved the city on the order of $10 billion," Jacob said. That's two-and-a-half times the daily economic output of New York City, he added.

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A 100-year flood

Jacob models the risks of extreme weather events and how climate change exacerbates them. He has been involved in long-term planning for sustainability, working with New York stakeholders including the MTA, New Jersey Transit and others.

Two years before Sandy, the NY governor's office commissioned areport on how the state should adapt to climate change. That report forecast the impact a 100-year flood— an event that has one-in-one-hundred odds of a occurring in any given year — would have on the city's infrastructure.

The study predicted that most of the city's subway tunnels would flood, probably in less than an hour. And if all 14 tunnels under the river were to flood, it would take about five days per tunnel to pump all the water out.

The MTA took these threats very seriously, Jacob said. "It was clear," in the run-up to Sandy, he said, "that the MTA really had taken notice of the risk and started to prepare."

Before Sandy hit, MTA employees moved their rolling stock (all vehicles that move on a railway) out of areas known to flood. Workers blocked off flood-prone subway entrances with plywood and sandbags.

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