The cost of creating better protection
Low-lying New York City, with all of its coastal development, is particularly vulnerable to those higher waters. In areas such as the Gulf Coast and eastern Florida that see more hurricane activity, flood walls, levees and even engineered wetlands help lessen storm impacts. There are proposals, for instance, to extend a dike around Galveston, Tex., to protect it from storms similar in magnitude to 2008's Hurricane Ike.
To fully protect Manhattan would require a flood wall that is tall, long and continuous, wrapping around the island on both sides, similar to the 16-kilometer-long, five-meter-high and nearly five-meter-thick (at its base) sea wall along the Galveston shorefront. In the aftermath of Hurricane Donna in 1960, such a sea wall actually was proposed for Coney Island—but never built.
That is not to say such a wall would be a cure-all. Even if such a defense were built, the wall could also function to keep water in as well as out during severe flooding, much as happened in Galveston after Hurricane Ike. Such an approach isn’t always popular for other reasons as well: it blocks ocean views. "You also have an aesthetic issue," notes geomorphologist Chris Houser of Texas A&M University.
In theory, nature’s protections—wetlands, forests and barrier islands—could blunt storm impacts. "It's like a sea wall but it's made of sand," Houser says of barrier islands and their dunes, his primary area of research. The way that such barrier islands jut out—their convex shape—acts as a break to storm surges, compared to the funneling effect of concave-shaped bays and inlets, such as those in New York Harbor. But there isn’t sufficient available real estate around New York City to restore natural defenses such as wetlands or forests.
Blocking the effects of future superstorms will require bigger-than-natural barrier islands, in any case. In Louisiana, for example, manmade barriers will be three times higher than naturally occurring islands to shield coastal property and oil and gas infrastructure. A similarly outsized manmade barrier island would need to be raised in New York Harbor.
That leaves possibly too-expensive alternatives, such as tidal barriers like the one in the Thames River to protect London or a massive system of levees, dikes and other water control structures, such as those in the Netherlands. But the Thames Barrier cost nearly $2 billion to build and some $10 million per year to operate. That kind of tidal barrier has been a dream of some New York City planners for at least a century, or more.
Adapting to climate change
As if all that weren’t enough to manage, there's the additional trial of coping with sea-level rise. Two major factors are at work in New York City. First, land rebounding farther north after the removal of the massive weight of Ice Age glaciers has caused the island of Manhattan itself to slowly sink. Second, at the same time, the oceans have risen by nearly three inches locally over the course of the 20th century, according to the U.S. Geological Survey. These changes will make creating long-lasting protection from storm surges even more challenging. "You're starting from a new zero," Rhome says. "The exact same storm is going to produce an even worse storm surge in a future time."