Rising waters set stage for more sea walls in US future

Gerald Herbert/AP/File
Joe Marshall, of the Southeast Louisiana Flood Protection Authority-West, secures a recently closed floodgate in Harvey, Louisiana, just outside New Orleans, in advance of Tropical Storm Marco on Aug. 24, 2020. Levee improvements since Hurricane Katrina in 2005 have improved the city's defenses.

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When Louisiana’s levee system held firm in August, protecting New Orleans residents from the risk of significant flooding during Hurricane Ida, it bolstered the notion that engineered defenses are a feasible way to mitigate some of the harshest coastal impacts of climate change. 

The complications are myriad – from challenges with funding and public support to questions of whether human engineering simply alters threats rather than removes them. 

Why We Wrote This

In past ages, conquering the seas meant venturing out toward known or unknown lands. Humans still do that, but today’s rising focus is on a defensive game – guarding coastal communities from storms and floods.

Yet in the minds of flood-risk experts, sea walls work – most of the time. U.S. coastal communities and the federal government have begun recognizing the changing risks. 

In Charleston, South Carolina, city leaders endorsed a $2 billion federal proposal to build an 8-mile-long sea wall to protect the city’s historic district. In Miami, the Army Corps of Engineers is researching the feasibility of an estimated $8 billion, 13-foot-high sea wall. Near New York City there’s a similar proposal that would cost up to $119 billion. And Texans are weighing a so-called Ike Dike system to protect Houston and the surrounding area.

William Merrell, an expert on coastal defenses at Texas A&M University at Galveston, says, “These large barriers are just going to be part of how we adapt to rising sea level.”

When Hurricane Ida made landfall on Aug. 29, the storm’s fierce winds left fallen trees scattered across southeast Louisiana like lawn clippings, while its heavy rains and storm surge threatened severe flooding. But in New Orleans a sense of relief was palpable: The city remained largely dry. 

Sixteen years to the day earlier, when Hurricane Katrina made landfall on Louisiana’s and Mississippi’s Gulf Coast, the aftermath was different. More than 1,800 people died due to structural failures in the region’s levee system, and tens of thousands of people who hadn’t evacuated found themselves flood bound in their New Orleans homes.

Why wasn’t Ida equally catastrophic? 

Why We Wrote This

In past ages, conquering the seas meant venturing out toward known or unknown lands. Humans still do that, but today’s rising focus is on a defensive game – guarding coastal communities from storms and floods.

Residents and experts alike say one big reason is the $14.5 billion in post-Katrina federal investment to expand and fortify the region’s levees and other flood walls. The effort worked. Where Katrina left a staggering $179 billion in damage in today’s dollars – making it the costliest U.S. weather disaster – this time levees staved off the worst of Ida’s predicted 12-foot surge. The result may be to confirm a model of flood preparedness that will be increasingly followed nationwide.

“It’s definitely a proof of concept,” says Nicholas Cali, the regional director of Southeast Louisiana Flood Protection Authority-West, which plays a role in maintaining the region’s flood risk management system. The system went “above and beyond what, I think, people had anticipated.”

Simply put, the success of southeast Louisiana’s levee system reinforces the notion that constructing sea walls is a feasible way to mitigate some of the harshest coastal impacts of climate change. 

Proposals rising from Gulf Coast to New York 

The complications are myriad – from challenges with funding and public support to questions of whether human engineering simply alters threats rather than removes them. Even well-designed systems can ultimately fail. 

Yet in the minds of flood-risk experts, sea walls work – most of the time. U.S. communities from the East to the West and Gulf Coasts have begun recognizing the changing risks and are pursuing defensive strategies, even as the federal government proposes action of its own. For many localities, it feels like the only choice. 

In Charleston, South Carolina, sea levels have already risen by 10 inches since 1950, according to estimates from the National Oceanic and Atmospheric Administration. Earlier this year, Charleston city leaders endorsed a $2 billion federal proposal to build an 8-mile-long sea wall to protect the city’s historic district. In Miami, where sea levels are expected to rise by 15 inches in the next 30 years, the Army Corps of Engineers is researching the feasibility of an estimated $8 billion, 13-foot-high sea wall. Near New York City, where Hurricane Sandy created a 13-foot storm surge in 2012, a similar proposal up to $119 billion would build a massive sea wall between Sandy Hook, New Jersey, and Queens, New York. 

“These large barriers are just going to be part of how we adapt to rising sea level,” says William Merrell, a professor at Texas A&M University at Galveston. Dr. Merrell is credited with being the first expert to propose the idea of building what’s become known as the Ike Dike, an estimated $26 billion project that would wall off the region from Galveston up to the shipping ports and refineries of Houston. 

David J. Phillip/AP/File
William Merrell, a professor in the Marine Sciences Department at Texas A&M University at Galveston, sits along Galveston Bay as he talks about the proposed Ike Dike project, on Sept. 4, 2020. Conceived in response to Hurricane Ike in 2008, the project is a coastal barrier that, when completed, would protect the Houston-Galveston region including Galveston Bay from hurricane storm surges.

Hurricane Ike tore into the Texas coast in September 2008, razing homes on Bolivar Peninsula when it made landfall due to a 20-foot surge in some areas. Nearby Galveston, while not spared from damage, was mostly still intact thanks to its own line of defense – a sea wall. 

That wall traces its roots to a devastating 1900 Galveston hurricane that cost as many as 6,000 lives. Many storms later, it’s in part the reason the city of Galveston still stands today. 

SOURCE: US Army Corps of Engineers
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Jacob Turcotte/Staff

The promise and the challenges

Building walls to protect humankind from the unforgiving seas is an ancient idea. In the first century B.C., Herod the Great of Rome ordered the people of Caesarea – in modern day Israel – to build an artificial sea wall and harbor that would serve as a trade port, by filling wooden barges with concrete and sinking them into the shallow water.  

The process worked, until Earth’s geology decided otherwise. (Unbeknownst to the Romans, there was a fault line under the harbor.) 

For all their potential, engineered barriers aren’t a fix-all solution for rising seas, some researchers say.  

A recent study by researchers at Stanford University’s Natural Capital Project, published in the journal Proceedings of the National Academy of Sciences, demonstrated how “gray” approaches to combating sea level rise – human-made infrastructure, like sea walls – can create unintended consequences for areas outside protected zones. The researchers used San Francisco Bay, where hydrodynamics differ from an open coastline, as their primary example. And by dividing the shoreline into small pieces, the researchers were able to model changes in the flood depth, coupled with the theoretical economic impacts. Their findings were concerning.  

“Our modeling showed that communities around the Bay could face additional flooding” after the addition of one large sea wall to the bay – with an estimated $723 million in added flood damage from just one high tide during spring, says Anne Guerry, a lead scientist in the study and chief strategy officer with the Natural Capital Project. 

After all, Dr. Guerry says, the water “has to go somewhere. It’s going to flow somewhere else.” 

The researchers’ findings are also applicable to closed bay water systems elsewhere in the U.S.

“There needs to be a regional conversation about who wins and who loses,” Dr. Guerry says. “Instead of making flooding worse for overburdened communities, let’s take a more regional approach where we think about using a combination of gray … and green infrastructure – natural systems like marshes and oyster reefs, and sea grasses and various types of coastal habitats.” 

Charting a future 

Climate-mitigation thought leaders find themselves daydreaming about what that future might look like, and what it will take to maintain functioning coastal societies. 

In Dr. Guerry’s view, the nuances of combining human-made and natural mitigation elements will increasingly become common knowledge – including plans to allow contained flooding inland rather than walling the sea off. She envisions a world where new communities are developed, but only after hard conversations are had about managed retreat. 

For Dr. Merrell, the construction Texans began on Galveston’s sea wall in 1902 will continue in new forms. First the Ike Dike. Then perhaps an extension of it farther down the Texas coast. Eventually, Dr. Merrell suggests, a series of climate-adaptive sea walls will dot their way along the Gulf and up the Atlantic and Pacific coasts. 

“I think what you’ll see is a concentration of wealth and population behind these barriers, and you’ll see relatively less building outside,” Dr. Merrell says. “It’s more like the medieval idea of you having this kind of walled in city and everybody runs in when the hordes come charging.” 

In the meantime, it’s about instilling confidence in the folks who are already behind the walls, says Mr. Cali, the SLFPA-West’s regional director. “The flood wall’s great. It worked. The levees are great. They worked. But every foot of real estate you put between that flood wall and the Gulf of Mexico makes it work better. It extends the life,” he says, of the protection we currently have.  

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