Isle of Palms Phase 3 Drainage Study and Improvements
Isle of Palms, SC
Thomas & Hutton completed studies and recommendations to improve drainage within the City’s Phase 3 area. Hydrologic and hydraulic modeling was performed using Advanced Interconnected Channel and Pond Routing (ICPR). Outfall improvement alternatives and internal basin improvements were developed with consideration of tidal intrusion and sea-level rise.
The drainage study resulted in the recommendation to improve the area’s three outfalls. All the outfalls discharge to the Intracoastal Waterway (ICWW) on the eastern edge of the island. The outfall improvements included larger diameter pipes and one-way check valves to prevent tides from penetrating inland and causing “sunny day” flooding. Two of the three outfalls are currently under construction and the third is in the permitting phase.
Recommendations for the study also include five internal drainage improvement projects that represented high-impact, low-cost improvements. The internal projects improved drainage to the outfall projects by removing “bottlenecks”, which allow stormwater to flow more easily to the outfalls. The internal drainage improvements ranged in size from a dual 42-inch diameter culvert to a local pipe system consisting of 18-inch pipes. Thomas & Hutton provided design (including utility relocations), permitting, bid support, and construction services for both the internal drainage projects, which are complete.
