Oyster castle built near Isle of Palms helps curb erosion

  • Monday, July 29, 2013

The U.S. Army Corps of Engineers Charleston District built an oyster castle north of the Ben Sawyer Bridge and south of the Isle of Palms Connector to help with erosion. COURTESY OF SARA CORBETT, USACE

There’s a castle across from the Isle of Palms. It’s probably not what you’d expect, though.

It’s 75 feet long, six feet wide and three feet tall. And, it’s made out of oysters.

The U.S. Army Corps of Engineers Charleston District built an oyster castle, which gets its name from the castle-looking structure that the oysters grow on, in late May 2012. Today, it’s thriving as an environmentally friendly way to curb erosion.

Alisha Timmons, a district biologist, volunteered to lead the project. “I was excited about it,” she said, “because I was born and raised here, so I wanted to do whatever to help our environment and keep it functioning properly.”

Once the castle was placed on the site, which is north of the Ben Sawyer Bridge and south of the Isle of Palms Connector, it took about three months for the spat, or baby oysters, to attach. The castle is a structure made from a mixture of shell, silica, concrete and limstone. “They (oysters) basically do all the work once you place it and lay it out for them,” Timmons said. “They find it – I don’t know how they find it – but they find it.”

The project assumed a risk of not working at all, though. The spat might not have attached and barnacles could have populated the area instead. But, Timmons was careful to make sure the spat had ideal growing conditions, which is between May and November.

“Once the oysters get established, the structure and the oysters attached to it, they’ll take the force of the waves and stop it from hitting the land,” she added. “Then, the sediment will accumulate behind the structure. It promotes the establishment of native species.”

The bank being protected by the oyster castle has improved by 0.29 of a foot. The oysters are not harvestable now, and might never be the centerpiece of a neighborhood oyster roast. The castle is marked by two signs 50 feet in both directions parallel with the bank that read: “Danger: Submerged Rock.”

“So far, this project is doing what it’s supposed to do,” Timmons said.

David Warren, a Charleston District project manager, oversaw the oyster castle development. Using leftover funds from previous years, he came up with six locations that could benefit. But, there was only enough money for one. The project cost was $178,000, which included regular monitoring of the site.

“We’d love to do more of these,” Warren said. The Army Corps of Engineers receives its budget from the federal government. Right now, the balance for the Atlantic Intracoastal Waterway (AIWW) is $0.

Warren makes a wish list for “budget defense” meetings and usually asks for $11-15 million of funding for the AIWW. But, because the waterway is used primarily for recreation and the annual cargo tonnage is less than 1 million, it isn’t prioritized.

The most recent figures for AIWW tonnage are from 2010 and it was 178 tons, according to a Charleston District spokesperson.

The alternative to curbing erosion is excavating, laying fabric and placing various sized-stones down, Warren said. For a price comparison, a project completed that way last year for a site of about 200 feet cost about $1,000 per foot. The oyster castle’s total construction cost – without monitoring and paying biologists which was $178,000 – was about $125,000, Warren estimated.

“Comparatively speaking, yes, this was more expensive, but the outcome was better,” he added. The excavating, fabric and rock method isn’t as environmentally friendly.

Warren pleaded his case for AIWW funding at a budget defense meeting last May. “We tout these little successes (the oyster castle),” he said, “but we don’t make the decisions about what we get.”

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