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Posted 7/16/2012

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By David Warren and Alisha Means
Charleston District

What is an oyster castle? An oyster castle is designed to be an instant habitat for oyster spat and growth. Oyster castle blocks are made of shell, limestone and concrete. The 12 inch by 8 inch square blocks are shaped in a tiered-structure that can interlock with each other to resist constant wave motion. It has been determined from previous studies that, in addition to providing immediate habitat for oyster growth, the placement of the castles fosters sedimentation behind them and encourages the re-growth of natural vegetation. This provides a shoreline erosion prevention benefit that is a mix of engineering and nature.

The Charleston District awarded a contract to Aerostar Environmental Service, Inc. in the amount of $178,000 to install oyster castles near the District’s disposal area just south of the Isle of Palms. On May 22nd, construction of the Atlantic Intracoastal Waterway (AIWW) Oyster Pilot Project commenced. The fully installed structure is 70 feet long by 6 feet wide and is constructed of approximately 800 blocks. The site will now be monitored for oyster recruitment and growth, the amount of sedimentation that occurs behind the castles and the degree to which vegetation is being reestablished behind the castle structure. Based on results of TNC projects, the Corps is optimistic that this type of project will provide a more cost-effective method of erosion control to protect dredge disposal areas along the AIWW while providing environmental benefits for oysters and other aquatic creatures.

Why is the Corps building oyster castles? As part of the Corps’ operation and maintenance responsibilities for the AIWW, the Corps must maintain disposal areas along the waterway for dredge material. These disposal areas have been experiencing growing impacts from shoreline erosion. Inspired by work done by the South Carolina Chapter of The Nature Conservancy (TNC) and the results they have seen from their oyster restoration work, Charleston District wanted to see if these types of projects could help protect our disposal areas while providing an added environmental benefit.

According to TNC, “oyster castles provide a viable alternative substrate for oyster restoration work in South Carolina and could prove to be a valuable assessment tool to determine optimal elevations, orientations and configurations of substrate for restoration and enhancement efforts prior to deployment of large- scale projects.”
Should this project prove successful, the Charleston District will look for future opportunities to partner with entities like TNC as a way to more cost effectively utilize our operation and maintenance money for the AIWW.

environment erosion oysters regulatory