King County, WA Environmental Rules: Erosion Control (2026)
Key Facts
- Seasonal limitation period
- October 1 through April 30
- Repair deadline after citation
- 24 hours to fix runoff
- Governing standard
- King County Surface Water Design Manual
- Applies to
- Unincorporated King County only
Summary
King County requires erosion and sediment control on every clearing or grading site, with stricter seasonal limits from October 1 through April 30, in unincorporated areas outside Seattle and other cities.
A. A person who clears, grades or otherwise disturbs a site shall provide erosion and sediment control that prevents, to the maximum extent practicable, the transport of sediment from the site to drainage facilities, water resources and adjacent properties. Erosion and sediment controls shall be applied as specified by the temporary erosion and sediment control measures and performance criteria and implementation requirements in the King County Surface Water Design Manual adopted in accordance with K.C.C. chapter 9.04.
B. From October 1 through April 30, which is the seasonal limitation period, clearing and grading shall only be permitted if shown to the satisfaction of the director that runoff leaving the construction site will comply with the erosion and sediment control measures and performance criteria and implementation requirements in the King County Surface Water Design Manual adopted in accordance with K.C.C. chapter 9.04 through a combination of the following:
1. Site conditions including vegetative coverage, slope, soil type and proximity to receiving waters;
2. Proposed limitations on activities and the extent of disturbed areas; and
3. Proposed erosion and sedimentation control measures.
Full Breakdown
Anyone who clears, grades or disturbs a site in unincorporated King County must control erosion so runoff doesn't reach drainage facilities, waterways or neighboring properties, following the King County Surface Water Design Manual. During the seasonal limitation period, October 1 through April 30, the director can restrict or expand clearing and grading based on site conditions, disturbed-area limits and proposed control measures, and requires an approved erosion and sediment control plan before work proceeds. If silt-laden runoff leaves the site or approved controls aren't maintained, inspectors issue a citation and stop-work order. Seattle, Bellevue, Kent, Renton and other incorporated cities enforce their own separate codes, not this one.
Violations & Fines
A citation and stop-work order issue immediately if silt-laden runoff leaves the site; problems not repaired within 24 hours escalate to a notice and order under K.C.C. chapter 23.24, which can halt clearing and grading until April 30.
Frequently Asked Questions
Does this cover construction sites in Seattle?
What happens if erosion control fails during the rainy season?
Sources & Official References
Other rules in King County
Compare King County to another location·View the Washington environmental rules overview
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