Marion County panel approves broad stormwater, floodplain code amendments with technical tweaks

The Marion County Land Development Regulation Commission on July 2025 approved a consolidated set of land development code amendments that revise stormwater, drainage and floodplain requirements across the county.

Stephen Cooney, Marion County engineer, and Jason Cambry, the county stormwater engineer, presented the package and walked commissioners through changes that affect when a major site plan or stormwater compliance is required, design-storm standards, culvert and pipe sizing, and recovery/attenuation requirements for open and closed basins. Chair (not named in the record) called for public comment after the presentation; no members of the public spoke. A board member made a motion to approve the grouped items with two modifications discussed in the meeting; the motion passed unanimously.

The measure bundles multiple specific technical edits intended to clarify applicability and to align county code with state and federal practice. Key changes highlighted by staff include new thresholds that apply the “lesser of” standard (35 percent impervious cover or 9,000 square feet) to major-site-plan applicability; explicit stormwater compliance when improvements “have the potential to adversely impact drainage, worsen flooding, or otherwise increase stormwater discharge to adjacent property;” and an exemption of existing single-family and farm parcels from major-site-plan review, while requiring stormwater compliance in their place.

The revisions adopt or reference external standards and data sources. Staff said the county is aligning some hydrologic inputs with NOAA Atlas 14 rainfall intensity data and moving away from an FDOT Zone 7 intensity reference. The code changes also incorporate Water Management District language for grandfathering improvements built before Oct. 1, 2013; FEMA requirements and Code of Federal Regulations criteria were cited in describing when a Letter of Map Change is required.

Technical and numeric highlights included in staff presentation and reflected in the adopted language: - Design storms: 100-year, 24-hour frequency-duration for open and closed basins; closed basins also incorporate a 25-year volume restriction and a 14-day recovery modeling period. Staff explained open basins are volume-restricted for the 24-hour event but may discharge beyond 24 hours because a positive outfall exists. - Exemptions and thresholds: parcels 10 acres and greater meeting five specified criteria may be exempt from certain requirements; bona fide agricultural uses remain exempt per the cited Florida statute; single-family lots within previously approved developments may qualify for simplified approval if five conditions are satisfied. - Shallow-area language: the commission agreed to a drafting clarification that “shallow areas” be defined as less than 1 foot in depth and less than 2 acres in size for waiver considerations. - Fees: staff said the county charge for stormwater compliance is $200 and the waiver request fee is $300. - Pipes/culverts: privately maintained storm pipes were reduced to a 15-inch minimum diameter, while publicly maintained systems remain at 18 inches; driveway culverts were set at 15 inches; minimum yard-drain diameter is 8 inches. Minimum easement and pipe-depth references of 10 feet were reaffirmed in the details. - Pond/berm design: minimum berm widths of 5 feet were adopted for proposed public stormwater facilities; steeper slopes for wet ponds (2 feet below water-surface elevation) may be approved by the county engineer; dry ponds retain a typical 4:1 slope unless otherwise approved.

Commissioners and staff spent extended time clarifying the closed-basin restrictions, how the 14-day recovery is used in models, and how documented downstream flooding would be validated by field observation before the county applies the more stringent closed-basin requirements. Commissioners expressed concern about removing narrowly defined waiver categories from the draft; staff responded that the language was changed so the county engineer may determine other limited waiver cases beyond the three prior examples.

Before the final vote, the commission agreed to two drafting clarifications made on the record: (1) the shallow-area waiver language change to less than 1 foot depth and less than 2 acres in size (agenda item 1.5); and (2) added language clarifying turn-lane lane-spread treatment in the lane-spread section (agenda item 1.6). A board member moved approval of the grouped items with those two modifications; another board member seconded. The motion “passed unanimously.”

The commission closed the meeting with no public comments and no further business noted. Staff said maps of county flood-prone areas used for these requirements will be maintained on the county GIS site and reiterated that certain applicants will be responsible for filing Letter of Map Change requests with FEMA “as soon as practicable but no later than six months after the date of availability of required technical or scientific data” when a floodway or BFE is affected.

The adopted amendments are technical in nature and staff said some elements will require further administrative interpretation (for example, whether modeled downstream flooding is validated by field observations). The changes also reference external approvals and federal standards, meaning some measures will be contingent on FEMA mapping, state water management district rules and other agencies’ criteria.

Votes at a glance: The commission approved the consolidated land development code amendments, with the two drafting clarifications noted above; the motion passed unanimously. The meeting record does not attribute the mover or seconder to a specific named commissioner in the transcript excerpt provided.

Looking ahead, staff and commissioners said implementation will follow existing permitting procedures; applicants with projects that change base flood elevations or floodways will remain responsible for pursuing required FEMA actions before final permits are issued.