Dorchester County adopts compensatory-storage rules for floodplain fill after staff, engineers and builders agree on revisions

Dorchester County Council on Tuesday approved Ordinance 25-15, which adds a compensatory-storage requirement to the county floodplain code to offset use of fill in the floodplain.

County deputy administrator Jason Formosano introduced the ordinance at third reading and said staff and outside engineers had worked on a revised draft after public comment and technical review. "We have provided for you all tonight as red lines in your packets, the proposed ordinance with revisions, based on really these collaborative discussions between staff and members of the engineering community," Formosano said.

Public works director Sunshine Traicus outlined substantive changes staff made after two weeks of review with the engineering community. Traicus said the red-line revisions (11 items in the summary) add a requirement for detailed hydraulic modeling for larger sites, allow limited relief for very small fills consistent with FEMA guidance, permit the use of stormwater best-management-practice (BMP) storage beyond the design storm when demonstrated by modeling, expand acceptable surveying approaches, require geotechnical verification of seasonal high-water tables, and clarify long-term enforceability and distinctions between public and private projects. "Item number 3 . . . is presented to allow for the use of BMP storage volume beyond the design storm events . . . subject to county approval, and it must be clearly demonstrated through some hydraulic modeling and engineering analysis," Traicus said.

Adrian Kane, CEO of the Charleston-Hilton Head Home Builders Association, urged council to adopt the ordinance and called for a broader watershed study. "I urge council to pass the proposed changes this evening so that we have a plan to move forward over the next coming years," Kane said, and said home builders and engineers supported a science-based approach to growth and compensatory storage.

Council members said the revised language responded to engineers' concerns while retaining county protections. One council member noted the draft drew from other jurisdictions' ordinances and that staff tightened language to reflect modern surveying methods such as drone-assisted surveys.

Council voted to adopt the red-line amendments, then approved Ordinance 25-15 on third reading as amended. The vote was unanimous; no roll-call vote with names was recorded in the public transcript.

The ordinance will require applicants building in regulated floodplain areas to demonstrate compensatory storage — generally through detailed hydraulic modeling — sufficient to preserve 100-year-event storage volume, subject to the county floodplain manager's review and FEMA-aligned standards. Staff also added explicit provisions for critical public infrastructure and for distinguishing public versus private project enforcement.

Councilmembers and staff discussed next steps including coordination with neighboring jurisdictions and a recommended regional watershed study to better understand cross-county flows and inform implementation.

The ordinance text, as amended, will be posted as part of the county code and staff said they will return with implementation details and permitting guidance as needed.