Climate Adaptation Climate Change Earth Science EarthSphere Blog Environment Hydrosphere Repost

Seawalls Are Not a Panacea

Climate Adaptation to Rising Seas

Published in The EarthSphere Blog. Cover Image: The Seawall by WM House; ArcheanArt)

Sea levels are rising, and the natural response of many people is to build walls and keep the water out. It sounds like a sensible idea on the surface, but the concept often frays under closer inspection. Financial issues like cost-effectiveness and availability of funds are usually the first barriers encountered. Then, there are the engineering aspects of any seawall project. A seawall that can’t keep out the sea is a failed venture from day one.

One thing seawalls have going for them is their conceptual convenience. Every voter can grasp the idea of a dam keeping water out. They are familiar with dams retaining water in lakes and reservoirs; surely, the process can work in reverse. Explaining to city residents how a big wall will hold back rising seas is easy, and everyone can get on board.

Well, maybe not everyone. Scientists and engineers familiar with the issues around enclosing large metropolitan areas with a series of seawalls and levees may raise some sticky technical issues. Then there are the suburban residents who might notice their communities are outside the wall, not inside. This observation will no doubt cause some consternation. They will not be comforted by an economic analysis showing how protecting their sprawling neighborhood is less cost-effective than protecting the inner-city urban areas.

Seawalls will probably form a partial climate adaptation strategy in some areas, but many other localities will need a different approach. Many cities along the Florida coast have eyed the possibility of protecting communities with seawalls. It’s an old idea.


Recent work at an archeological site off the coast of Israel uncovered the earliest known example of a seawall. A wall designed to keep back the rising tides. At a location currently several meters underwater, a Neolithic community battled the seas by building a 100-meter-long wall of boulders at the water’s edge. Our ancestors fought and lost this battle about 7,000 years ago.

More recently, Florida residents living at sea level have finally embraced climate change and are looking for solutions. A report by Resilient Analytics and the Center for Climate Integrity projects the State will need $76 billion for seawall construction by 2040. Ron DeSantis recently made a half-hearted commitment to provide $270 million, or 0.35% of the required funds.

But some scientists are skeptical that Florida can outrun climate change with walls and pumps. They point to the leaky limestone foundation much of the State is built upon. The technical problem is caverns and cracks in the limestone, allowing seawater to flow under most seawalls and flood the very communities the walls are trying to protect. It’s like constructing a boat with small holes in the bottom. Eventually, it will sink.

No one is willing to spend the required money on seawalls in other cases. Smaller communities always prefer building a seawall to abandoning their homes, but they can’t necessarily afford it. The Army Corps of Engineers has issued ultimatums to some localities: either force people from flood prone communities or forfeit federal funding needed to fight climate change and flooding in more concentrated urban settings, where money spent on protection makes sense. New Jersey has already taken action. The government recently bought seven hundred flood-prone homes in New Jersey, and the residents were required to relocate.


Large seawalls are expensive, and ultimately the benefits must justify the costs. The Center for Climate Integrity estimates that by 2040 seawalls to protect US coastal cities larger than 25,000 will cost $42 billion. This figure rises to $400 billion if we include the smaller communities.

The size of the community makes a difference in spreading the cost. Protecting Jacksonville, Florida, would cost $3,990 per capita, but the cost for protecting New York City drops to $231 per capita. Cost-effectiveness is why New York can consider a six-mile-long seawall to protect the city from storm surges like Hurricane Sandy. 

This mega barrier would take 25 years to complete, but some critics believe sea levels are rising so quickly the seawall would be obsolete soon after completion. The barrier also creates a series of new ecological problems and ultimately might trap the city’s sewage and waste inside the barrier for the entire city to enjoy.

There are no easy answers, and any proposed solution to the threat sea-level rise poses for our coastal cities will have its pros and cons. None of this makes seawalls impossible, but the idea of protecting all our coastal cities with seawalls is a non-starter.

Cities should include seawalls in their long-range planning process, but they also need to have a plan B.

Related Reads:

A Retreat From Climate Change (by WM House; Archeanweb)



U.S. Flood Strategy Shifts to ‘Unavoidable’ Relocation of Entire Neighborhoods (By Christopher Flavelle; The New York Times)

Trump Administration Presses Cities to Evict Homeowners From Flood Zones (By Christopher Flavelle; The New York Times)

Walls Won’t Save Our Cities From Rising Seas. Here’s What Will (By Joseph Bennington-Castro; NBC News) 

Who Will Pay for the Huge Costs of Holding Back Rising Seas? (By Jim Morrison; Yale Environment 360) 

Climate Costs in 2040 (Source:Center for Climate Integrity ) 

The $119 Billion Sea Wall That Could Defend New York … or Not (By Anne Barnard; The New York Times) 

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.