Sullivan’s Island’s stormwater drainage system, installed decades ago by the South Carolina Department of Transportation, is now struggling to keep pace with modern environmental challenges. Much of the infrastructure is clogged, deteriorating or simply not designed to handle the increasing volume of rainfall and high tides the island has experienced in recent years—issues expected to worsen with climate change and vertical land subsidence.
To address these concerns, the civil engineering firm SeamonWhiteside (SW+) was tasked with developing an island-wide stormwater master plan and infrastructure improvement strategy. Aaron Aiken of SW+ presented the firm’s findings to Town Council on Tuesday, Jan. 28.
The report revealed that much of the island’s drainage infrastructure is significantly undersized, with large portions rendered ineffective due to clogging. As part of their research, the firm gathered photos and feedback from residents, which they say provided invaluable data for validating their findings and could bolster future federal and state grant applications.
Currently, Sullivan’s Island has approximately 55,000 linear feet of stormwater pipes. If SW+’s recommendations are fully implemented, that figure will nearly double to 92,000 feet. The proposed improvements are designed to extend the functionality of the island’s stormwater system through 2074, ensuring effective flood mitigation for the next 50 years. SW+ estimates an annual maintenance cost of $4 million in today’s dollars.
The plan recommends 18 projects, categorized into two groups: high-priority improvements that require immediate action and future extensions to expand the system’s surface area over time.
“It’s no surprise to me as an engineer that Osceola Avenue ranks high on this priority list,” Aiken said. “Much of that is due to tidal intrusion, which comes over the roadway—and as time goes on, it’s only going to get worse.”
To address this, SW+ recommends raising Osceola Avenue by 18 inches at its lowest point and installing a new stormwater collection system that will channel water to a pump station at Station 10. The estimated cost for this segment is $9.8 million.
Other high-priority areas include Station 22 ½ and Station 26 ½, both of which require upgrades to larger pipes and the installation of a tidal backflow preventer, estimated at $1.8 million and $7 million, respectively.