Coastal challengesFor Flood-Prone Cities, Seawalls Raise as Many Questions as They Answer
The U.S. Army Corps of Engineers, whose mission includes maintaining waterways and reducing disaster risks, has recently proposed building large and expensive seawalls to protect a number of U.S. cities, neighborhoods and shorelines from coastal storms and rising seas. As a scientist who studies the evolution and development of coastlines and the impacts of sea level rise, I believe that large-scale seawalls, which cost billions of dollars to build, are almost certainly a short-term strategy that will protect only a few cities, and will protect only selected portions of those cities effectively.
The oceans are rising at an accelerating rate, and millions of people are in the way. Rising tides are already affecting cities along low-lying shorelines, such as the U.S. Atlantic and Gulf coasts, where sunny-day flooding has become common during high tides.
The U.S. Army Corps of Engineers, whose mission includes maintaining waterways and reducing disaster risks, has recently proposed building large and expensive seawalls to protect a number of U.S. cities, neighborhoods and shorelines from coastal storms and rising seas. Charleston, New York City and the Houston-Galveston metro area are currently considering proposals to build barriers in response to hurricane surges and sea level rise, and the Corps recently published a draft proposal for a seawall for Miami.
As a scientist who studies the evolution and development of coastlines and the impacts of sea level rise, I believe that large-scale seawall proposals raise important long-term questions that residents, urban leaders and elected officials at all levels of government need to consider carefully before they invest billions of dollars. In my view, this approach is almost certainly a short-term strategy that will protect only a few cities, and will protect only selected portions of those cities effectively.
Coastal Flooding Is Here
The extent of high tide flooding in low-elevation Atlantic coastal cities is well documented, and so are future trends. In a 2017 study, the Union of Concerned Scientists assessed chronic flooding risks in 52 large coastal cities and found that by 2030, the 30 cities most at risk can expect at least two dozen tidal floods yearly on average. The study defined tidal flooding as seawater encroaching into at least 10% of a city.
These cities include New Haven, Connecticut; Boston; Philadelphia;, Washington, D.C.; Baltimore; Wilmington, Delaware; Norfolk, Virginia; Charleston, South Carolina; Savannah, Georgia; Jacksonville, Florida; and Miami. Cumulatively, they are home to about 6 million people. The study projected that by 2045, most of them will experience over 100 days of flooding annually.
This flooding won’t just become more frequent – it also will become deeper, extend farther inland and last longer as sea levels continue to rise. Greater encroachment will cause increasing harm to infrastructure, development and property.
