A collaborative push to address flood-prone areas of Isle of Palms and beach erosion on the back side of the island has seen SeamonWhiteside (SW+) pour their energies into recommending effective resilience measures.
On the heels of offering a final presentation of their sea level rise strategy at the March Isle of Palms City Council meeting, SW+ reps Ryne Phillips and Colleen Williams have identified a key factor causing coastal erosion — septic systems.
These residential wastewater treatment and disposal mechanisms that are not connected to a public sewer system occupy most of the lowest areas on the island. It's in these parts, said Phillips, where much of the flooding and tidal inundation happens.
"You've got to get rid of septic systems so that they don't overflow and [bring] sewage. It's not just the flooding, it's a water quality public health issue," stated Phillips who serves as the SW+ Water Resources Team Leader.
The architecture and civil engineering firm is currently interfacing with the Isle of Palms Water & Sewer Commission in securing federal funding to get the island off septic systems and linked to a sewer network.
In addition to septic systems, recounted Williams, the City is working off its 2023 Master Plan focusing on drainage improvements. The plan features a multi-use path elevation project on Waterway Boulevard, as the City is in the process of acquiring a release from each abutting homeowner prior to breaking ground.
"So, what we tried to recommend were improvements that supported these ongoing efforts. So — three categories: programs, policies and projects. We talked about every new development be tapped into a sewer line, and not a septic field," Williams continued.
The SW+ Land Planner went on to detail green infrastructure solutions in terms of advising the City to require increased tree canopy to stabilize the soil and create pervious surfaces. In addition, Williams and her colleagues have recommended living shorelines, rain gardens and private incentive programs, all in the pursuit of dissipating flood water in an aesthetically pleasing manner.
SW+'s blueprint — formally adopted by City Council in March — projects what the firm "absolutely needs to happen" by 2040 in order to line up their stormwater infrastructure solutions by 2050.
Activities in progress to mitigate erosion include the constant replacement of lost sand spearheaded by Steven Traynum of Coastal Science & Engineering (CSE).
On that front, CSE is working alongside the US Army Corps of Engineers (USACE) to renourish the beach, particularly along Breach Inlet.
"The USACE is currently placing sand along the south end of the island as part of a beneficial use project to improve navigation of the intracoastal waterway," said Traynum in a email to the Moultrie News.
"They plan to place 550,000 cy (cubic yards) of sand over the course of several months, with most of the material being placed along the mid to low-tide beach. The project is likely to continue through most of the summer. The City has secured another contractor to redistribute some of this material into a restored dune between Breach Inlet and 10th Avenue. That work is ongoing and will likely be completed in early May."
One issue with that, Phillips noted, is the Army Corp's unique requirements for contractors to redistribute their sand. Those specifications from the federal agency have driven up prices for contractors "astronomically," according to Phillips.
"If you want to live on the beach, on the salt, on the Isle of Palms, where it erodes, they're going to invest millions and billions," reported Phillips. "The sea level rise, on the backside of the island and the marsh ... I think the real solution is preventing that tidewater from coming inland through pipes."
The Clemson grad went one step further in arguing in favor of prohibiting people to build in low-lying areas or, at the very least, require them fortify and elevate before construction.
On that note, Phillips credited the City for its earnest attempts to elevate, enhance land mass and preventing water from penetrating the island's interior.
"But you can't protect one little point, right? Like if there's one crack in the wall, the wall fails as a whole. And that's with most coastal cities, not just Isle of Palms," he explained. "We just randomly keep putting our finger on the cracks and more cracks keep forming."
Both Phillips and Williams suggested that the continued implementation of new gray infrastructure (roads, buildings, pipes) and green infrastructure will be instrumental in handling high tides.
Or more specifically, as Phillips observed, their mission will demand a balancing act of using traditional pipes to remove tidal water and green infrastructure (rain gardens, bioswales, etc.) to keep water from pooling and ponding along local roads.
Added Williams: "If we can reestablish some marsh on the backside of the island that helps prevent erosions, that helps slow down the influx of water."
To view SW+'s Sea Level Rise Adaptation Plan, visit https://www.iop.net/sea-level-rise-adaptation-plan.