A City at Sea
Published: September 25, 2005

As we read about the effects of Hurricanes Katrina and Rita on the Gulf states, we have to wonder if the same thing could happen to the metropolitan region. Scarily, it could.

New York City is not as low-lying as New Orleans, but much of it is less than 10 feet above sea level, including the perimeter of Manhattan's business district; the Lower East and West Sides; parts of the F.D.R. Drive; Bellevue hospital; coastal Queens and Brooklyn, including Coney Island, Rockaway, Jamaica Bay and La Guardia Airport; and the shores of the upper East River.

Across the Hudson River in New Jersey, Hoboken, Port Elizabeth, Newark Liberty Airport and Hackensack Meadows are particularly susceptible to flooding. During the December 1992 northeaster, ocean water flooded the Hoboken train station, short-circuiting the entire New York City subway system. PATH trains were stranded beneath the Hudson River. It was 10 days before the transportation system was brought back into full operation. The F.D.R. Drive was flooded. Sewers backed up. And this was not even a full-blown hurricane like the one in 1938 that devastated much of southern Long Island and the coast of New England.

Unfortunately, the 1992 storm is probably only a warning of worse to come. The scientific consensus had been that sea level is rising along the Eastern Seaboard at about one foot per century, but more recent predictions by NASA scientists at the Goddard Institute for Space Studies in New York City say that with climate change and global warming, sea level will rise as much as an additional one and a half feet by 2050.

What this means for New Yorkers is that in the future, relatively modest storms riding on an ever-increasing sea level will do as much damage as rare, once-in-a-century storms do now. New York City, New Jersey and Long Island, particularly the low-lying south shore, are at great risk.

So what can be done? European nations with low-lying coastal communities have grappled with this problem for years, but they have usually taken concrete steps only after serious, prolonged floods that caused catastrophic loss of life and property. Several countries have constructed storm surge barriers that can be raised to block off the ocean until the threat passes.

Storm surge barriers are giant floodgates that lie flat on the sea floor or retracted at harbor entrances, river mouths or coastal inlets. When an emergency is declared and before the storm surge hits, the barriers are rotated or slid into position and locked, acting as temporary levees.

The Thames Barrier near London has been used effectively more than 80 times since 1982 to hold back North Sea storm surges. And the Dutch are the masters of coastal engineering, dyke construction, reclamation of land and flood protection measures using surge barriers (half of the Netherlands, including Amsterdam and Rotterdam, lies below sea level). After debating the issue for more than 20 years, the Venetians are finally building inflatable barriers to close off the Venice lagoon, which opens into the surge-prone Adriatic Sea. And Russia is completing an extensive system of barriers to protect St. Petersburg from storm surges arising in the eastern Baltic Sea.

There are already some modest storm surge barriers in the northeastern United States in places like Stamford, Conn.; Providence, R.I.; and New Bedford, Mass. And a storm surge barrier could work for New York City, as well.

Three barriers would be needed to protect the city since storm surges can penetrate New York Harbor directly from the ocean, from behind Staten Island and from Long Island Sound. Barriers should be built across the Narrows, which is about one mile wide, under or near the Verrazano-Narrows Bridge; west of Staten Island near Perth Amboy, N.J.; and across the upper East River near the Throgs Neck Bridge where the river is about two-thirds of a mile in width. These three barriers, high enough (not less than 25 feet above sea level) to withstand any conceivable storm surge, closed before a major storm would provide a ring of shelter around the city.

But many questions remain. Such barriers would represent an engineering project of a scale rarely contemplated in the United States. The cost would be in the billions of dollars. Communities outside the barriers would remain exposed and unprotected, including Kennedy International Airport and Long Island's south shore. Wind, rain and upland flooding damage would still have to be endured.

Professional scientific and engineering societies, environmental groups and the City of New York should take advantage of the shocking images of the destruction of New Orleans and the Gulf Coast to start planning protection for citizens and services in a climate-changed future. The question is not if a catastrophic hurricane or northeaster will hit New York, but when.

Malcolm Bowman is professor of oceanography at the State University of New York at Stony Brook and head of the Stony Brook Storm Surge Research Group.