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Charleston needs to better plan how Army Corps wall fits into the city, consultant says

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Consultants hired by Charleston to review a proposed seawall around downtown said the city needs to be more proactive about making sure the structure works over the long term, or risk being disappointed by the end result.

The project will work best if leaders map out how the hurricane surge barrier fits with drainage projects and other work, said Andy Sternad, an architect and the project manager for consultant Waggoner & Ball.

"The city doesn't really have that visibility right now," Sternad said.

Sternad's firm is leading a team hired by Charleston to respond to the $1.75 billion Army Corps of Engineers proposal. The Corps unveiled a first-draft study in April proposing an 8-mile looping wall around much of the Charleston peninsula, a breakwater in the harbor south of the city and high-powered stormwater pumps. It's the largest-ever proposal to handle flooding in the city.

The plan, which would go through years of adjustments before construction, spurred questions: Will it trap rain inside the city? Will it push hurricane-surge waves to nearby suburbs and islands? What will it look like?

Some of those questions won't be addressed until the official design phase, which could come in a few years with a fresh round of congressional funding. Some will be addressed for the first time in the coming months, as the Corps releases an "optimized" plan. A Corps spokeswoman said those results will be presented to the public in February or March.

But the Waggoner & Ball team told the city at the end of 2020 that it needs to be more assertive with the Corps. The firm wrote that the adjusted wall alignment as of December did "not function in the City’s long-term interest for adaptability and internal storm water management," including waves that might make it over the wall.

Waggoner & Ball was instrumental in the recent Dutch Dialogues process, which explored how to manage water in four flood-prone sections of Charleston.

As to whether Charleston can make the Corps project fit with its overall goals, "I’m not sure that the city is on that path today, but the door is still open," Sternad said. 

The analysis suggests a delicate balancing act for the city, in part because the Corps is only tasked with fixing one problem: the surge of ocean water that hurricanes send onto land. Charleston faces multiple flooding threats, including chronically poor drainage, excessive rainfall, and rising tides driven by climate change. 

"I will continue to encourage the Corps to further partner with us to consider the drainage aspect of all this, in addition to the surge and sea-level rise aspect," Charleston Mayor John Tecklenburg said.

But if the project ever comes to fruition, it requires not just the consent of the city but the Corps itself. The engineering group has its own set of cost-and-benefit determinations and mandates from Congress to follow before it can approve the proposal and ask lawmakers to fund it. Their involvement has so far provided a fully paid-for study, and would cover 65 percent an approved project's costs.

"The city is aware of Waggoner & Ball’s concerns," said Mark Wilbert, chief resilience officer for the city of Charleston. "We’re actively working with the Corps on all of their concerns."

Gates and canals

Waggoner & Ball's analysis unveiled an early tension in the wall design: whether to closely follow the edge of the peninsula, or place the barrier in marsh and water. Aligning the wall too tightly to land "potentially cut(s) off opportunities to solve storm water problems in the future," Sternad said. 

But there are environmental implications to putting the wall farther out. During last summer's public comment period two federal agencies worried the plan would damage marshes that serve as a nursery for fish and other animals.

The wall's path directly affected an estimated 26 acres of salt marsh, in particular as it sliced through pluff mud along the Ashley River. Placing a wall there, even with some openings to allow tides in and out, could cause erosion and the disappearance of cordgrass, the U.S. Fish and Wildlife Service said in a letter to the Corps. 

The Joe.JPG

Marshland seen behind Riley Park on Wednesday, Jan. 6, 2021 in Charleston. Andrew J. Whitaker/Staff

Causing marsh damage also adds to the cost of the project, because every acre must be paid for in mitigation credits from a bank that restores the same type of wetland. 

The Corps' updated alignment now avoids more marsh. But for Sternad, building the wall tight to land raises other issues. It makes it harder for the city to manage rainfall, which wouldn't be able to run directly into the harbor (the Corps has proposed high-powered pumps for this purpose). Moving the wall out, and effectively creating an interior canal, would make it easier to drain water, Sternad said. 

A tighter alignment also means the wall could cut across Lockwood Drive. The low-lying thoroughfare is one of the first streets in the city to flood and in moving the wall closer, the Corps now suggests crossing the road just south of the James Island expressway, and creating a gate that would be closed during the most severe tidal flooding. 

But the dozens of gates that the Corps has already suggested in other areas for tidal flow, vehicle traffic and pedestrian crossings all add to the cost over time, Sternad said, because the city will be responsible for closing, opening and maintaining them. In its first draft report, the Corps said operations and maintenance for the protection system would cost almost $5.6 million a year.

"There should be an ambition to have no vehicle gates and no rail gates," Sternad said.

Rising tide

A wall that sits on high ground also provides less wiggle room if a hurricane wave overtops it. The water would wash directly onto the city behind it, instead of flowing into a canal or holding area first, Sternad said.

It's a possibility that the wall might be overtopped. The height selected by the Corps — 12 feet above mean sea level, or about 3 feet above the High Battery — would protect against most storms, but not the highest surges of 1989's Hurricane Hugo, which landed north of the city. The Corps has said making the wall higher is cost-prohibitive, because it would require lifting or gating overpasses for U.S. 17 and Interstate 26. 

But at its current proposed height, the wall faces not only hurricanes but also a moving baseline. Future sea-level rise will make it even more likely that surge waves wash over. 

High Battery

People walk and tour the High Battery Wednesday, January 6, 2021. Brad Nettles/Staff

Waggoner & Ball analyzed this possibility in its review. According to the firm's preliminary simulations, a 12-foot wall would have a roughly 6 percent chance of being overwhelmed between now and 2030, a 24 percent chance between now and 2040, and a 37 percent chance between now and 2080. The Corps is only designing a wall to last for 50 years, but even if the project is eventually funded, it may not be completed for many years after that. Thus, it would have to last well beyond 50 years from today.

This means it's crucial that the wall is designed so it can be added on to in the future, Sternad said. "As the water's coming up, the wall has to rise with it," he said. 

Corps spokeswoman Glenn Jeffries said the wall will be "adaptable," but to what extent is undecided. Only in the next design phase would project managers decide how much the wall could be altered after it is built, she said.

The public square

Although the public is eager for information, the Corps has offered few updates since the summer on its revised plan. 

That's led to a recent call for a citizen group to track the project's progress. Susan Lyons, a founder of the flood advocacy group Groundswell, said she's contacted several members of City Council and the mayor to ask for such a panel. 

"There was this huge vacuum in the public square between April (when the plan came out), and the wintertime," Lyons told The Post and Courier. "It's just been very much behind the scenes, and it's not right."

Tecklenburg said he thought a citizens group was "a great idea," and that he wants one to be formed. He said that the Corps' coming update is "a great time for everybody to dig in and focus on it."

There will be more opportunity for input, too. The Corps' has promised to hold another public comment period after it officially presents its adjusted plan in late winter or early spring. After that, Charleston will have to make a commitment to move forward with the project, including indicating how it may pay for its share of the cost. Charleston's deadline to do that was originally in May but will likely be pushed back, said Jeffries, of the Corps.

If the feasibility study is signed by high-level Corps officials after that, most of the details will come in the next phase, which rounds out the design, including the look of the barrier and its exact location.

More public engagement is exactly what needs to happen, Sternad said. Most importantly, the city needs to lay out how the wall fits with drainage work and other flood projects in each section of the peninsula.

"If the city can organize that process and create a framework plan before this next (design) phase, then it can take charge of its destiny," Sternad said.

Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.

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