The East Coast Is Extremely Vulnerable to Hurricane Flooding

Hurricane Joaquin could be headed right for the U.S. East Coast this weekend. Models so far fail to agree on where the storm might make landfall, but shorelines from North Carolina to Massachusetts are possible targets for the high rise of ocean water, or surge, that hurricanes push ahead of them. Even if the storm veers east in the Atlantic Ocean, an unusually large atmospheric pressure gradient near the storm is destined to push strong winds onshore for many hours, bringing an extended period of high surf and heavy rain, forecasters say.

Either scenario could cause flooding because many large cities and valuable beachfronts along the coast are situated only a meter or two above sea level. The map below, developed by Scientific American, shows how far inland a surgethat is one meter high (red) or six meters high (yellow) would reach. Although a six-meter surge would be rare, one to three meters is common for Atlantic hurricanes; the biggest surges from Superstorm Sandy were four to five meters high.

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The map shows how sea level rise could affect the coast over many years. But a storm surge of the same height would reach just as far inland. And it would come in the course of a day.

The most practical way to protect long stretches of shoreline between cities is to pump sand from offshore deposits onto beaches every five to 10 years to replace the sediments that tides, common storms and hurricanes wear away. It is unclear, however, whether enough deposits exist with the right grain size to hold a beach or dune, for repeated reconstruction for more than a few decades. And as the map shows, much of the East Coast is also slowly subsiding, making flooding more likely over time.