Drum Island Mitigation Site Design Peer Review
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Project Objective

To construct the new Hugh Leatherman Terminal in Charleston, South Carolina, the South Carolina Ports Authority (Authority) designed 22 acres of wetlands mitigation. The Authority hired ATM, a Geosyntec Company, to conduct a comprehensive peer review of this site design with a focus on value engineering to control costs and suggesting project enhancements to support successful mitigation.

Geosyntec’s Scope of Services

ATM reviewed and modified designs, data, construction plans, and specifications to create a more practical and successful project. Using numerical modeling, ATM showed how interior constructed waterways could bring tidal exchange to the 22 acres of enhanced, restored, and created saltwater wetland. ATM also reviewed coastal structures to consider improvements to their sections and materials. Major design modifications were recommended, resulting in possible significant savings, compared to the original construction estimate.
As part of the final construction project, the abandoned dredged material disposal island was restored by removing material, regrading to natural elevations and creating a tidal creek system, replanting with indigenous species, and protecting erosive shorelines with rock armoring and oyster-bag living shorelines. Centrally located in Charleston Harbor, the island will function as an intertidal marsh, helping to maintain water quality and provide a habitat for juvenile fish, other marine species, and birds.

Notable Accomplishments

A major reason the Authority sought a peer review was to reduce the overall costs of the project, especially the cost of rock armoring for the proposed inlets. ATM determined that one inlet was redundant and relocated the other inlet to a less erosive area, where much less armoring was needed. Long-term and short-term erosion hotspots were also identified for protection.
Construction was completed in July 2019 and the project was recognized by the American Council of Engineering Companies of South Carolina with a 2020 Engineering Excellence Award.