What’s in a Wall?
Rising seas, strengthening storms and eye-popping real estate growth have forced Charleston to consider extreme steps to protect its downtown peninsula, the engine of the state’s relentless tourism industry.
To do nothing is a nonstarter, and would risk billions of dollars in storm damage and gamble the city’s priceless cultural history.
But, a leading alternative poses many of the same risks: Forking over billions of dollars, all with an unknown impact on the city’s landmark coastlines.
By the end of March, the U.S. Army Corps of Engineers is set to deliver an updated $1.75 billion plan to protect the Charleston peninsula from storm surge for 50 years using an 8-mile sea wall. It’s a drastic measure that even some critics admit is needed in some form. Others believe it could do more harm than good.
One thing is for sure: Bigger, more frequent storms won’t stop, regardless of whether there’s a wall in Charleston to meet them.
Naturally Wet
Perimeter defense proposals for the peninsula figure prominently in the findings that came from a series of meetings and workshops in 2019 called Dutch Dialogues. The resulting study, endorsed by Charleston City Council in early 2020, depicts a system of measures designed to help drain water quickly to minimize negative human impacts in all parts of town, from the Eastside and hospital district to rural Johns Island.
Proposed changes to the Low Battery sea wall have been part of the city’s response to sea level rise
“The final report urges local governments, businesses, developers and residents to make a coordinated effort to work with water instead of against it,” City Paper reporter Heath Ellison wrote in October 2019.
A holistic approach to managing water, according to the report, would require a layered system to harness natural topography, store surface water runoff and reengineer critical low-lying infrastructure to minimize problem areas.
Mentions of rigid flood-prevention measures in the Dutch Dialogues report are paired with suggestions to find multiple uses for new man-made water-control features — not-so-subtle reminders of nature’s humbling inevitability.
“Land that was once naturally wet, will be again,” the 252-page report states, at one point.
Studying Feasibility
City of Charleston and Army Corps officials are upfront that a potential sea wall would primarily be aimed at mitigating damage from storm surge downtown, not preventing nuisance flooding.
But, that’s not to say there won’t be any secondary, everyday benefits.
“You can’t put a wall up around a city to keep water out, if you get 3, 4, 5, 6 feet of sea level rise, and say that it’s not going to be helpful,” said Mark Wilbert, the city’s chief resilience officer.
Currently, the Corps is working through a three-year, $3 million feasibility study that began in 2018 to find out exactly what it would take to protect a city like Charleston from flooding events. It all comes down to money — potential damages must exceed the cost of a project to prevent them. The Corps’ draft analysis estimates its $1.75 billion sea wall system could prevent $4.7 billion in damage over the estimated 50-year lifespan of the project.
Federal funds could cover up to 65% of the cost, leaving the city on the hook for the balance — more than $612 million. Local funding sources have not yet been determined.
By the end of March, the Corps is also slated to present new findings and account for potential negative impact of added infrastructure downtown on surrounding communities.
“Right now we’re working on the optimization … refining our tentatively selected plan,” said Wes Wilson, project manager for the U.S. Army Corps of Engineers. “Reducing the uncertainty and risk and doing our due diligence on our analysis on that tentatively selected plan.”
The current proposed barrier is intended to protect downtown from a storm surge of up to 12 feet. Storm surge refers to water driven onshore above natural water levels by powerful storms. That flooding can be compounded if a storm rolls in during high tide, which can drive sea level increases of more than 7 feet on its own.
(The draft plan does not call for a 12-foot wall in all locations, according to the Corps. Some higher-elevation areas might only need shorter barriers to prevent local flooding.)
Army Corps modeling shows a 12-foot wall would protect from the 9.39-foot storm surge downtown experienced during Hurricane Hugo in 1988 and Hurricane Matthew, which pushed 6.15 feet of water onshore in 2016.
The 8-mile protection barrier would be built in three phases around the peninsula, from northern Morrison Drive to Wagener Terrace. Outlying communities like Bridgeview Village and Rosemont would get help from “non-structural measures,” according to the Corps. Raising homes when possible in those communities and floodproofing vulnerable structures that can’t be raised are all in the cards.
A breakwater proposed to sit just offshore has been deemed unfeasible and will be eliminated from the Corps’ plans going forward, according to Wilson.
Early-stage renderings that depict utilitarian, military-grade perimeter protection will likely change with local input as the process moves into its engineering and design phase in the coming months.
Still, some are skeptical that the proposed plan could deliver on the promise of helping stop flooding catastrophes without significant trade-offs.
Have a Say
To civil and environmental engineer Joshua Robinson, there are unanswered questions about the Army Corps’ proposal, but the community needs to weigh in on fundamental questions before moving on to specifics.
“I think the biggest, the most important issue for Charleston, at this stage, isn’t so much about what it’s going to look like, or specifically where it’s located,” Robinson said. “I think the bigger question, and the fundamental question is, what’s it going to do?”
During the Corps’ spring 2020 public comment period, Robinson’s firm used downtime during the pandemic to assemble its own report critical of the agency’s draft study, pointing to data that showed the wall could very well be too short in a major storm. In a Post and Courier op-ed, Robinson said the wall plan was a wrongheaded response to the Dutch Dialogues.
“Where we have the capacity to work with nature on the peninsula, we must,” he wrote.
Options for Battery storm surge measures
Since then, a separate analysis of the Corps’ plan drafted by the engineering firm Waggonner & Ball also shows an 11.8% risk that a storm would come close to overtopping a 12-foot wall by 2040 — within a decade of its completion. That risk increases each decade, up to 37.1% by 2080, the end of the proposed project’s lifespan. (Robinson’s firm assisted on the Waggoner and Ball analysis.)
For the past decade, residents downtown have wrestled with how to deal with sea level rise and increasing nuisance flooding. Winslow Hastie, the leader of the Historic Charleston Foundation, said the impacts of the changing climate make a perimeter protection plan “non-negotiable.”
His group helped fund and organize the Dutch Dialogues and the most recent Waggonner & Ball study, and Hastie said it’s imperative that local groups push the sea wall plan to be as effective as possible.
“The Army Corps, let’s be honest, is not really well known for designing beautiful things that people like to hang around,” Hastie said. “It’s utilitarian. They’re really looking at this from a cost-benefit ratio and risk reduction.”
Once the project does enter the design phase, Hastie believes Waggonner & Ball’s analysis will give the city the flexibility it needs to go back to the Corps with changes and end up with a favorable outcome.
“My advice is simply to stay engaged because it is a big deal,” Robinson said. “It’s a big deal financially, it’s a big deal in terms of the future of the city.”
“It doesn’t have to be a take it or leave it sort of proposal,” he said. “But it’s a partnership between the city and the federal government. And so that means we have a say in making edits and changes based on what serves our community.”
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