Brunswick County to seek public comment on proposed stormwater ordinance updates including larger buffers and 100-year design standard

Brunswick County commissioners on Oct. 6 directed staff to update the county stormwater manual with new rainfall data and scheduled a public hearing on broader ordinance changes for Nov. 17.

County stormwater staff told the board the county could replace its existing, countywide rainfall values with site-specific estimates from NOAA Atlas 14, the National Weather Service’s authoritative precipitation-frequency dataset. “NOAA Atlas 14 is the authoritative source of precipitation frequency data for the U.S. … it uses historical precipitation data to generate its frequency estimates and is specific to actual locations in the county,” the presenter said.

The presenter said the Atlas 14 values are generally higher than the county’s current figures, which date to the ordinance that went into effect in February 2002. Staff asked for permission to update the manual immediately with the Atlas 14 data so designers could use the most recent, location-specific values when sizing stormwater controls.

Why it matters: staff said more current, location-specific rainfall data will give engineers more accurate inputs for stormwater-sizing calculations. Commissioners and residents previously have raised concerns about uneven rainfall across the county; staff noted Atlas 14 produces values specific to a project’s location rather than a single countywide number.

Major proposed ordinance changes discussed include: • Making the 100-year, 24-hour design storm a required standard (rather than a recommendation) for pond sizing in many developments; staff warned that requiring the 100-year standard could increase the footprint and cost of stormwater control measures and could make very small sites difficult to develop unless exemptions are provided. Staff said exemptions for small commercial sites could be considered if engineers demonstrate an inability to meet the standard. • Increasing riparian buffers from 30 feet to 50 feet measured from intermittent and perennial streams, ponds, lakes and other water bodies, and prohibiting stormwater control structures inside that buffer. Staff noted the current 30-foot requirement is written into both the manual and the ordinance, so any change would require an ordinance amendment and a public hearing. • Adding a 20-foot horizontal buffer for delineated, regulated wetlands measured perpendicular to the wetland boundary. Staff said regulated wetlands are delineated and approved by the U.S. Army Corps of Engineers during design and permitting.

Commission discussion focused on implementation and equity across the county. Commissioners asked how Atlas 14 handles widely varying local rainfall patterns and were told the dataset uses station-specific historical measurements so a project in Leland would use Leland’s Atlas 14 values rather than those for a different part of the county. Commissioners also asked how to treat small sites if the 100-year requirement were adopted; staff suggested a minimum-size threshold and said they could craft an exemption process that still required a designer to demonstrate the constraint.

The board voted to schedule a public hearing on the ordinance changes for Nov. 17 and directed staff to proceed immediately with updating the stormwater manual to incorporate NOAA Atlas 14 rainfall data. The public-hearing scheduling was approved by voice vote; the record did not include a roll-call tally.

Next steps: staff will prepare ordinance language and supporting materials for the Nov. 17 public hearing and will return to the board with the proposed ordinance changes and any recommended exemptions or minimums for small sites.

Speakers quoted in this article are identified from the meeting record and appear as named in the transcript.