Environmental Rules in Williamson County, TN (2026)
5 county-level rules, plus city-specific rules for 1 city in Williamson County, Tennessee.
Verified from official government sources
Stormwater Management
Williamson County runs a Phase II MS4 stormwater program under a TDEC permit, protecting the Harpeth River watershed. Every development must detain excess runoff on-site so post-development flows do not exceed the natural rate.
Williamson County Stormwater Management Rules
Some RestrictionsWilliamson County Zoning Ordinance, Art. VII, Sec. 7220.A
Each development shall provide for the on-site or off-site detention of excess stormwater runoff resulting from that development.
Erosion Control
Williamson County requires erosion plans for significant earthwork and forbids development from sending more stormwater onto downstream neighbors. Post-development flows cannot exceed the peak rate, volume, or velocity of the land in its natural state.
Williamson County Grading & Drainage Rules
Some RestrictionsWilliamson County Zoning Ordinance, Art. VII, Sec. 7220.B
No development shall cause downstream property owners, water courses, channels, or conduits to receive stormwater runoff from proposed developments at a higher peak flow rate, at higher volumes, or at higher velocities than would have resulted from the same storm event occurring over the site of the proposed development with the land in its natural, undeveloped condition.
Coastal Development
Williamson County is landlocked in Middle Tennessee, so coastal rules do not apply. Development near its streams and drainageways is instead governed by open-space buffers, floodplain limits, and erosion controls protecting the Harpeth River system.
Williamson County Waterway & Buffer Rules
Some RestrictionsWilliamson County Zoning Ordinance, Art. VII, Sec. 7113.A
Fifty (50) percent of the drainageway shall be maintained as open space. Drainageways shall be protected in such a way that the entire length can continue to function and be used for drainage purposes.
Flood Zones
Any development in a Williamson County Area of Special Flood Hazard needs a development permit before work starts, under Zoning Ordinance Article 19. The rule reaches only the unincorporated county, and its flood maps rest on FEMA's Flood Insurance Study dated December 20, 2024, an amendment date confirming the standards are current, not the county's 2012 baseline.
Williamson County Floodplain Development Permit Rules
Significant RestrictionsWilliamson County, TN, Zoning Ordinance § 19.02(A)-(D)
(A) APPLICATION: This Ordinance shall apply to all areas within the unincorporated area of Williamson County, Tennessee. (B) BASIS FOR ESTABLISHING THE AREAS OF SPECIAL FLOOD HAZARD: The Areas of Special Flood Hazard identified within Williamson County, Tennessee, as identified by FEMA, and in its Flood Insurance Study (FIS) dated December 20, 2024... are adopted by reference and declared to be...
Flood Elevation Requirements
New construction and substantial improvements in a Williamson County AE flood zone must have the lowest floor, including any basement, built at least one foot above the Base Flood Elevation. Section 19.04(B) applies the same one-foot freeboard to residential buildings and to elevated or floodproofed non-residential buildings alike.
Williamson County Base Flood Elevation Freeboard Rule
Significant RestrictionsWilliamson County, TN, Zoning Ordinance § 19.04(B)(1)(a), (2)(a)
a) In AE Zones where Base Flood Elevation data is available, new construction and substantial improvement of any residential building (or manufactured home) shall have the lowest floor, including basement, elevated to no lower than one (1) foot above the Base Flood Elevation... a) In AE Zones, where Base Flood Elevation data is available, new construction and substantial improvement of any comm...
Environmental Rules by City in Williamson County
1 cities in Williamson County have their own environmental rules rules. Each link goes to that city's dedicated page with code citations.
All Williamson County ordinances
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Williamson County Ordinance Hub →