Crews are closing in on completion of the last phase of the $70 million Low Battery Seawall Repair in Charleston, South Carolina, as officials already report earlier sections have protected property along the lower peninsula from storms and high tides.
“It ended up successful and popular,” said Matthew Fountain, Director of the Department of Stormwater Management for the city, explaining that it helps everyone to better enjoy the area while offering flood protection for residents.
“We’ve seen no flooding since we started work on the project, which is a huge improvement,” said Laura Boisclair, Project Manager for designer Johnson, Mirmiran and Thompson (JMT), an employee-owned company with offices in Charleston. “Not only does it look nice, it actually works.”
The city originally built the Low Battery in two stages as part of a development project, one stage opening in 1911 and the other in 1919. The developer built into marshland, filling behind the seawall to create an upscale neighborhood. Timber deck and timber pilings supported concrete panels.
The city completed a structural assessment after some hurricanes came through several years ago. Some of the timber was still good, and others had been over drilled and needed replacement.
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“There were some structural issues with the [existing] wall — nothing at the point of imminent failure but showing clear signs of deterioration from 100 years of impacts on the seawall,” Fountain said. “The city knew we needed to do something to restore and repair or make it more resilient and improve the corridor.”
The Stormwater Management Department teamed up with other entities, including the water and sewer utility and the city Parks Department, to support the mile-long project, which will feature a linear park, bicycle lanes, speed tables, and additional water outflows. The team used tourist tax dollars.
“We did a lot of things for not nearly as much money as if we had done the individual things [separately],” Fountain said. “It was still an expensive project.”
JMT surveyed the area to determine what was needed and then designed a new Low Battery seawall. Included in the city’s requirements was to plan for an expected sea level rise of 2.5 feet and the Americans with Disabilities Act guidelines for sidewalks and handicap parking.
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The new seawall sits a consistent 9.5 feet above sea level. Different parts of the wall needed raising more than others, from about 1 foot to 2.5 feet.
The city divided the project into four phases to limit the negative effects on traffic and residents of the area. The road, Murray Boulevard, provides the only access to homes adjacent to the project.
“It made for a longer overall project but a shorter impact on the road and those along the road,” Fountain said. “You have to balance what you can do.”
Gulf Stream Construction of Charleston received the contracts for all four phases. They began by installing the concrete micro-piles, using core machines, through the existing foundation. JMT selected the micro-piles to avoid the noise and vibration associated with pile driving so close to the historic homes in the area. Crews then grouted the small-diameter piles into the ground. The team used glass fiber reinforced polymer (GFRP) material rather than steel reinforcing bar for structural support.
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“Utilizing fiberglass has been huge,” said Jerry Martin, Superintendent at Gulf Stream. “It’s easy to use and a lot lighter [than steel].”
While lighter, GFRP provides as much support as steel. It can be carried around, not needing an excavator or crane to move it. That speeds up installation time, according to Martin.
“The guys can pick it up and carry it with their hands,” Boisclair said. “This is one of the first projects that the City of Charleston allowed the product.”
In the first phase, the contractor used a mixture of GFRP and steel, but in later phases, just GFRP was used. It costs about the same as steel. However, it cannot be bent in the field; everything must be prefabricated at the plant. That did not create any issues on this project.
“The city and the contractor were happy with it,” Boisclair said.
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Crews placed shotcrete on the front of the wall. Then they created the walking platform and removed the old seawall, including taking out the old timber piles. The contractor brought in sandbags and used a silt bag to protect the water in the harbor. The city monitored water quality throughout the project.
Work on the 5,000-foot-long seawall took place in 100-foot sections to reduce the area’s exposure from storms or high tides. Crews cut the existing seawall at the foundation, then at low tide, the contractor used an excavator to remove each section of wall and haul it off site. Sometimes two weeks could pass without a low enough tide to work on the wall, said Paul Capps, Senior Project Manager at Gulf Stream.
The project has included replacing the old water main, installing a sanitary sewer, completing other utility work, and creating a linear park with benches and look-out areas.
During construction, the city converted the two-way road to a local-traffic-only, one-way road, removing the grass median to give crews more room to work and ensure access for residents in the area. Then they built back the one lane. Once that finished, traffic switched to the new lane and work commenced on the other lane.
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“During this last phase, everyone involved on the entire project learned a little something in all of [the] previous phases, and all worked together on the last phase to make sure everything was as perfect as we could make it,” Capps said. “Our core team has been together.”
Gulf Stream has completed Phase 4 work on the seawall and will focus this year on making road and utility improvements and installing decorative elements for the complex park. Crews are paving with asphalt. This last approximately $20 million section was let using a construction manager at risk contract.
“[Gulf Stream] has been a great partner and has done excellent work on the project,” Fountain said. The company “has done it as a point of pride to do something for the community.”
The project promotes resiliency, improving drainage and protecting residents from flooding. Crews added an outfall and added filtering water quality devices and check valves in all of the updated outfalls. Water quality filtration units that flow into the Charleston Harbor were added in the road.
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“Overall, the construction went very well,” Martin said. “Every phase has been on time and under budget.”
This last phase sits in front of the entrance to the public park, White Point Gardens. The new park will have a bus loading area, parklets, additional landscaping, and a new streetscape.
“One of the biggest elements the city is proud of is how many things we were able to leverage with one project,” said Fountain, explaining that the department tried to build the best project possible that was beneficial as well as cost effective.
The project was designed and built to extend the Low Battery seawall higher in the future.
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“It’s designed for today’s problem with an eye toward what might be needed in the future,” Fountain said.
Boisclair calls it a “once in a lifetime” project and added that “it will be around for hundreds of years.”
Capps, a Charleston native, considers it an honor to have worked on the project. He said it will be a jewel for the city.
The city and contractor expect the current project to complete by mid-year 2025. The Low Battery is now the same height as the older High Battery.
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“People go out there and say, ‘This is great, beautiful,’” Fountain said. “One of our points of pride about the project is building something that everybody is excited about.”
