Williamson County, TN Environmental Rules: Erosion Control (2026)
Key Facts
- Plan Trigger
- 500 cubic yards earthwork
- Neighbor Drainage
- Cannot increase runoff
- Standard
- Match natural flow
- Retaining Walls
- May need permit
Summary
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.
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.
Full Breakdown
Grading is regulated through the same resource-protection article as erosion and stormwater. Earthwork above 500 cubic yards, fill over three feet, or excavation over four feet needs a soil erosion and sedimentation control plan (Section 7230). Section 7220 bars any development from discharging stormwater to downstream owners, watercourses, or channels at a higher peak rate, volume, or velocity than the undeveloped site would have produced. Drainageways must keep functioning, retaining walls and detention basins may be required, and the owner maintains on-site drainage facilities long-term.
Violations & Fines
Grading without a plan stops work and brings fines. Redirecting drainage onto a neighbor or downstream property requires corrective action; slope failures from bad grading leave the owner liable for repairs.
Frequently Asked Questions
Can my grading send water onto a neighbor?
Do I need a permit for earthmoving?
Sources & Official References
Other rules in Williamson County
Compare Williamson County to another location·View the Tennessee environmental rules overview
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