Kiawah Island council, planners and residents workshop stormwater rules after county, conservancy and KICA briefings

Kiawah Island town staff convened a joint Town Council and Planning Commission workshop to review stormwater management, hear technical briefings from Charleston County and local specialists, and seek guidance on possible supplemental stormwater standards.

Charleston County stormwater official Chris Wanamaker told the group the county’s delegated MS4 program focuses on water quality and applies more stringent controls than the baseline state standards (DHEC/DES). Wanamaker said county practice includes peak-rate and volume controls, downstream analysis for development, and requirements tied to impervious-area triggers; he noted MS4 designation depends on census urbanized-area criteria and state decisions and that Kiawah currently does not qualify for MS4 status.

Kiawah Island Community Association engineers described the island’s drainage network and operations. Matt Hill, lakes supervisor, said the island has roughly 122–125 ponds (about 350–360 surface acres) connected in ~15 drainage basins; two major outfalls (near Beachwalker Drive and the Canvasback/fire-station area) convey about 70% of the island’s runoff. Ryan Elmer, KICA senior civil engineer, said KICA performs routine maintenance, bathymetry surveys and spot dredging, and has increased annual drainage maintenance spending from roughly $300,000 in earlier years to about $1,000,000 in 2024.

KICA described gate operations and upgrades: many old aluminum flap gates have been replaced with Tideflex valves, and two large outfalls already have remote-control motors so staff can raise and lower gates from an app. Elmer and Hill cautioned that gate timing is constrained by tides (draining is possible only around low tide windows), automation requires reliable communications, and pre-storm drawdown can trade increased stormwater capacity for ecological risks on the ponds.

“KICA’s analysis suggested we need to begin pond drawdown operations for roughly a 25‑year design storm to provide appreciable storage,” Elmer said. Hill added that rapid mixing from drawdown and inflow can reduce dissolved oxygen and can cause fish kills; he said lowering ponds can also mobilize sediment and contribute to erosion around outfalls.

On water quality, presenters described routine testing with SCDNR’s algal ecology lab (algae abundance and fecal‑coliform monitoring) and periodic fish‑tissue sampling (including emerging contaminant screens such as PFAS). Lee Bundert of the Conservancy summarized recent state shellfish-area assessments showing restricted shellfish harvesting in parts of the Kiawah watershed and said bacteriological and turbidity impairments have been documented in some basins.

The Conservancy presented land‑cover analysis showing Kiawah’s upland impervious cover at roughly 18% (hand-digitized estimate), above the unadjusted NOAA CCAP estimate of ~15%. Bundert noted ecological research showing that watershed imperviousness above roughly 10–20% begins to produce measurable water‑quality and habitat changes, and that moving past ~20–30% often produces larger, less‑reversible impacts; he said the island has roughly 70 upland acres of impervious capacity left before crossing the Conservancy’s modeled 20% threshold.

The workshop closed with policy discussions. Staff said the planning commission had forwarded a recommendation on draft supplemental stormwater standards (covering pervious elements and on‑site retention) and that the item now sits with council. Participants debated “carrot and stick” approaches — incentives, education/outreach, and mandates for new development — and discussed implementation questions such as how to enforce BMPs, require on‑site retention, or provide incentives for pervious driveways.

Next steps: staff will post slides and materials online, the planning commission will continue discussion at its next meeting, and council will decide whether to formalize the draft supplemental standards into an agenda item for further consideration.