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…