U.S. 17 Spring/Fishburne Drainage Improvement Project
The goal of this project is a significant reduction in the duration, frequency, and severity of flooding caused by moderate to heavy rainstorms along the Septima Clark Parkway and throughout the Spring Street and Fishburne Street drainage basins by Summer 2023.
Once complete, the system will be able to move 360,000 gallons per minute from the Charleston peninsula to the Ashley River.
As a result of the new outfall, the system will initially work under gravity, increasing the flow rate by up to 7 times its existing capabilities by the end of Phase 4. Following the installation of the pumps during Phase 5, the flow rate will be increased up to 10 times.
Phase 4 construction includes an outfall comprised of triple 8ft by 10ft box culverts extending 500ft into the Ashley River. The outfall will be below low tide so as to remain hidden from view and was designed to ensure that there would be no erosion.
Drop – Shafts
Eight drop shafts were installed in phase 2 to convey flow from the surface to the deep tunnel. The intent of these is to spin the water into a vortex as it enters the drop shaft to prevent air from entering the tunnel system.
Phase 4 construction includes a wetwell measuring 137ft long, 55ft in diameter, and 40ft deep.
75 million dollars of work will be awarded to local businesses.
Tunnel Boring Machine
Phase 3 used two tunnel boring machines to excavate the ground. The larger of the two was 15 feet in diameter and nearly 300 feet long with all of its components.
5400ft of 12ft tunnel, 2950ft of 8ft tunnel (which includes the drop shaft tunnels which connect the drop shafts to the tunnels).
Phase 3 construction included four shafts up to 30ft in diameter and 180ft deep.