Union County, NC Environmental Rules: Stormwater Management (2026)

170 governs drainage and stormwater management for every project in unincorporated Union County, meaning land outside the corporate limits and extraterritorial jurisdiction of Monroe, Indian Trail, Waxhaw, Weddington, Stallings, Wesley Chapel, Marvin, Mineral Springs, Unionville, Wingate and Marshville. The section opens with natural drainage systems: development must conform to the natural contours of the land, and natural or pre-existing human-made drainage ways must stay undisturbed unless the county expressly approves otherwise. Lot boundaries have to line up with those drainage ways so a lot cannot be built only by altering them.

General drainage standards require every development to carry a drainage system adequate to prevent undue retention of surface water, and they bar channeling surface water into a sanitary sewer. Drainage systems must connect to surrounding drainage ways or streets wherever practicable, and drainage swales, curbs, gutters and storm drains must meet NCDOT construction standards. No fence or structure may be built across an open drainageway in a way that reduces or restricts water flow, and the administrator can require a stormwater facility to sit inside a recorded drainage easement wide enough for maintenance.

The core numeric limit sits under the Stormwater Management heading: a development cannot impede natural flow from higher adjacent land, cannot redirect its own surface water's natural flow to a different location (added by the 5-18-2015 amendment), and for any project disturbing more than one acre of land or more than a quarter acre of impervious area, the post-development discharge rate at the property boundary cannot exceed the pre-development rate for the 2-, 10- and 50-year storm events (added by the 10-21-2024 amendment). 180 before construction, building permits or final plat approval can proceed.