Next year, New York will break ground on the first section of a U-shaped wall around Lower Manhattan built to guard against the next Hurricane Sandy. Some believe so-called “gray” infrastructure projects like this one represent the future of climate resilience — imposing, impenetrable and decidedly humanmade. Others believe resilience should take on a greener hue.
New Orleans is preparing for storm surges by creating a series of wetland terraces that will absorb floodwater from neighboring streets. The state of Louisiana is working to resurrect coastal wetlands around the Big Easy that have been lost to the sea. These structures will supplement the city’s system of levees and canals.
Natural structures defend against storm surges more deftly than concrete barriers. Rather than throw up a shield against an oncoming wave, “living shorelines” feint and parry, absorbing the impact over a broad expanse. According to a 2012 study, a “sufficiently wide and tall vegetation canopy” can reduce flooding by up to 40 percent, meaning shorelines endure less damage and recover more quickly from severe storms. Natural defenses also support biodiversity by lending a home to birds, fish and other creatures.
Living shorelines offer another important advantage. Levees and dams, built to control flooding, have contributed to the loss of wetlands around New Orleans. Historically, the Mississippi River delivered silt to low-lying terrain, replenishing lands at risk of sinking below the water. Levees have since confined the path of river, guiding sediment away from disappearing wetlands and straight into the Gulf of Mexico.
Today, 14 percent of U.S. coastline is rimmed by concrete. The specter of rising seas will prompt the construction of even more expensive and obtrusive manmade barriers, like the embankment planned for Lower Manhattan. In an effort to cut costs and preserve ecosystems, the Army Corps of Engineers is looking to expedite the approval of living shorelines, making it easier to develop natural structures able to fend off storm surges.
This is a fundamentally different approach to infrastructure and one that will not work in all places. But, where possible, communities are nurturing shoreline ecosystems better suited to a changing climate — wetlands, swamps and mangroves that can keep pace with sea-level rise for decades to come.