Before the Flood

While London had been building up the embankments along the Thames since the late nineteenth century, the 1953 storm galvanized Westminster to ensure that Britain’s first city was adequately protected. It took thirty years to build the Thames Flood Barrier, a 520-metre safety valve located about five kilometres east of the Isle of Dogs. Clearly visible in satellite photographs, the barrier consists of nine conch-shaped piers, between which swivel twenty-metre-high, steel-plated flood-gates. Engineered to withstand a storm that would only be likely to occur once in 1,000 years, it has been closed more than 100 times.

The Dutch, who have spent centuries building extensive dikes and canal networks to protect a country carved out from the sea, responded to the 1953 disaster with similar gravitas. Between the 1960s and the 1980s, the government built numerous protective barriers in strategic locations, including an extraordinary three-kilometre-long sluice gate across the Eastern Scheldt, a flood-prone river delta in Zeeland, south of Rotterdam. The Dutch engineer their barriers to withstand a 10,000-year storm. “They don’t mess around,” says Bowman. “It’s a question of national security.”

New York, for its part, sits on a tropical hurricane path and has been repeatedly slammed by major storms over the past century, including the 1938 Long Island Express. But the city has done surprisingly little to protect itself, besides building seawalls around LaGuardia Airport, and producing a new emergency evacuation plan in the aftermath of 8/8. Why? Bowman tells a story about meeting senior engineers for the Port Authority of New York and New Jersey, the agency that manages the city’s airports, tunnels, bridges, and ports, and whose assets are highly vulnerable because they’re at or below sea level. “They were all very polite and interested in what we had to say about sea level rise and storm surge barriers,” he recounted. “But [they said] it’s long term and we have more immediate things to worry about.” The meeting took place at the World Trade Center, a week before 9/11.

In light of subsequent events — imagined (as in The Day After Tomorrow, a 2004 blockbuster that portrayed the cataclysmic submergence of Manhattan) and then real (New Orleans) — Bowman’s proposal has begun to attract more serious scrutiny from the climate change experts and media. Even Mayor Michael Bloomberg’s long-term climate change plan for the city, released in April 2007, openly acknowledges the risk posed by long-term sea level rise. But there is scant official enthusiasm for a barrier that would be both monumental and monumentally expensive.

Klaus Jacob, a Columbia University geophysicist who worked on the 8/8 report for the mta, shares Bowman’s unease about the city’s blithe resistance to the lessons of storms past and the threat of future flooding. He says the kind of infrastructure now being planned — e.g., a third tunnel into Penn Station — is based on maps created in the 1970s that show the theoretical upper extent of water infiltration in the event of a 100-year storm. “It’s outright inexcusable,” Jacob says, peering over his heavy black glasses. Yet he does not support the idea of a barrier. “It’s just not sustainable — not financially, nor from an engineering point of view.”

The Verrazano Narrows barrier, for example, would have to have a base as long as a football field anchored to the bottom of the harbour, which is 100 metres deep. (By contrast, the Thames Barrier sits on a riverbed that’s only six metres below the surface.) And if New York asks the federal government for funds to finance a series of storm surge barriers, other vulnerable cities — Boston, Miami, San Francisco — will demand equal treatment. Combined with necessary maintenance expenses, to avoid a New Orleans–type disaster, the costs are just too high.

Perhaps getting to the heart of the mta advisory panel’s ambiguous warning, Jacob adds that engineered solutions “freeze in the risk.” In other words, given the alarming but ultimately unpredictable acceleration of climate change, there’s no telling how long a given barrier would afford the necessary protection (even if it were properly maintained), and therefore such structures create a false sense of security and a heightened risk for those who depend on them.

In Jacob’s view, coastal cities won’t win the long war against an angry climate. He says the Netherlands, which relies heavily on engineered solutions, has adopted a pragmatic and flexible approach tailored to an uncertain future. Of course, the government closely regulates its seawalls and storm surge barriers, all of which are built to withstand storms of almost unimaginable severity. But in recent years, Jacob says, Dutch authorities have admitted that these protections have limitations: as the seas rise, it’s neither possible nor cost effective to continue building them up ad infinitum.

Instead, Dutch architects are now experimenting with dwellings moored to posts and designed to float on concrete pontoons, as a way of responding to the threat of flooding. Meanwhile, the government has opted to allow controlled “overtopping,” permitting the sea to breach existing shoreline dikes (covered in reinforced grass, to prevent erosion) and seep into nature reserves beyond. The aim of such approaches is to accommodate flooding, to work with rather than against climate change.

New York’s situation is obviously different, but Jacob nonetheless argues that his city must “put land use planning in the context of climate change.” In other words, when New York considers waterfront development or the deployment of subsurface infrastructure, it should anticipate where flood zones could extend decades or centuries hence. The city’s population will likely grow by a million within the next twenty-five years, and, Jacob says ominously, “When we try to look for places to put those million people, we must aim for areas we won’t have to give up soon.”