November 27, 2012

NYC flood protection a complex task

Many changes large and small can help, but even then some areas will be vulnerable, experts say.

By Adam Geller, The Associated Press

 

click image to enlarge

A raised ventilation grate doubles as street furniture installed to limit subway flooding from rain on Hillside Avenue in the Queens borough of New York. The raised grates were designed to deal with flooding from rain, not the deluge generated by Superstorm Sandy.

The Associated Press/Metropolitan Transportation Authority

NEW YORK - Inside tunnels threading under a Houston medical campus, 100 submarine doors stand ready to block invading floodwaters.

Before commuters in Bangkok can head down into the city's subways, they must first climb three feet of stairs to raised entrances, equipped with flood gates.

In Washington, D.C., managers of a retail and apartment complex need just two hours to activate steel walls designed to hold back as much as a 17-foot rise in the Potomac River.

If metropolitan New York is going to defend itself from surges like the one that overwhelmed the region during Superstorm Sandy, decision-makers can start by studying how others have fought the threat of fast-rising water. And they must accept an unsettling reality: Limiting the damage caused by flooding will likely demand numerous changes, large and small, and yet even substantial protections will be far from absolute.

Sandy's toll is overwhelming. But finding the money and political will to build a proposed system of giant storm barriers at the mouth of New York Harbor will likely be very difficult. Even at a cost of up to $27 billion, such barriers would leave large parts of the region unprotected.

So government, businesses and property owners will need to consider taking smaller steps -- on land -- to minimize the impact of flooding, with or without sea barriers.

The good news is that many cities have already learned much about how to limit the damage from floods. Researchers are working on still other strategies, like 16-foot-wide inflatable plugs being developed at West Virginia University to seal off subways and tunnels from water.

But there's no single cure-all.

"You really have to go with a series of levels of protection. You can't just buy into one engineer's dream of building" a 5-mile-long barrier for New York Harbor, said Phil Bedient, a flood expert at Houston's Rice University whose research was key to shoring up that city's defenses after it was swamped by Tropical Storm Allison in 2001. "So you have to pick your spots carefully. And you really can't protect everything."

Sandy's destruction in the New York area highlights a host of weaknesses that must be addressed, experts said. But the region's size, density and geography will complicate the task.

"It's hard to predict what's going to happen, where it's going to happen and what magnitude, and that leads to a quandary of what makes sense to do," said William Coulbourne, a Delaware structural engineer specializing in flood plain design and construction. "New York City is unique in the number of people who live there, the age of the buildings, that it's on islands and it's a hub of U.S. commerce."

That could force people to make trade-offs they might have been unwilling to consider before Sandy.

When city officials met with real estate and construction industry representatives starting in 2008 to look at making New York buildings more environmentally efficient, the conversation included whether to move flood-prone electrical equipment out of basements in apartment buildings and office towers to higher floors, said Rohit "Rit" Aggarwala, former director of the city's Office of Long-Term Planning and Sustainability.

"One of the people from the real estate industry said, 'Rit, you're crazy. That's rentable space up on those floors,' Aggarwala said. "That's the problem of thinking in the near-term of losing revenue vs. the long-term certainty of needing it."

Now New York needs a wide-ranging discussion, considering not just how to limit damage to high-rise districts like lower Manhattan that are critical to the region's function, but about whether and how to rebuild in residential neighborhoods along the shoreline, said Larry Buss, a recently retired hydrologic engineer for the Army Corps of Engineers who for many years led its committee on non-structural flood-proofing.

(Continued on page 2)

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