Island County, WA Environmental Rules: Stormwater Management (2026)
Key Facts
- Applies to
- All development activity, unincorporated county
- Open-channel setback
- 7.5 feet from structures
- Closed-facility setback
- 5 feet from structures
- Major project threshold
- 5,000 sq ft or 2 acres
- Illicit connections
- Banned under § 11.03.350
- Enforcing agency
- Planning and Community Development Director
- Criminal penalty
- Up to $1,000 fine, 90 days jail
Summary
Island County's stormwater code regulates drainage from nearly every development in the unincorporated area, from single-family lots to major subdivisions, requiring a drainage plan, mitigation for downstream impacts, and setbacks between structures and drainage facilities before Public Works signs off on a building or grading permit.
A.Stormwater entry and exit. If drainage patterns currently exist on the site, drainage facilities must be designed so that stormwater enters and exits the site at the existing location(s) of entry and exit.B.Mitigation. Mitigation must be provided for drainage impacts resulting from changes in the flow rate and quality of stormwater runoff, and in the case of a critical drainage area from changes in the volume of runoff. ... F.Setbacks from drainage facilities.1.Open drainage facilities. A setback of at least seven and one-half (7.5) feet, measured horizontally, shall be provided between any structure, on-site or off-site, and the top of the bank of a constructed open channel or open retention/detention pond.2.Closed drainage facilities. A setback of at least five (5) feet, measured horizontally, shall be provided between any structure, on-site or off-site, and the nearest edge of a closed drainage facility.
Full Breakdown
020. 200 sets the baseline drainage system requirements for every project with a drainage plan or narrative: stormwater must enter and exit a site at its existing natural drainage points, and any impact on flow rate, water quality, or runoff volume must be mitigated, with extra mitigation required inside a designated critical drainage area. 5 feet from the top of the bank of an open channel or retention/detention pond, and at least 5 feet from the edge of a closed drainage facility. 030: "small residential development" and "other small development activity" create less than 5,000 square feet of new impervious surface, while "major development activity" hits that threshold or disturbs two acres or more.
130 before permit approval, reviewed for water quality, peak discharge, and flooding impacts. 190, and the Public Works Department administers the drainage manual referenced throughout the chapter. 350 separately bans using the county's stormwater system, natural or artificial, to dispose of anything but stormwater, and prohibits any connection to it from inside a building. 360 to verify compliance.
Violations & Fines
Island County Code § 11.03.340 routes every chapter 11.03 violation to the Planning and Community Development Director for enforcement under § 17.03.260, the same enforcement chapter that covers erosion and grading. A willful stormwater violation, including an illegal connection to the county's drainage system under § 11.03.350, is a misdemeanor carrying up to a $1,000 fine and 90 days in jail, and the Director can add a civil penalty of up to $500 per day and suspend or revoke the project's permits until the drainage deficiency is fixed.
Frequently Asked Questions
Do I need a drainage plan to build a house in unincorporated Island County?
How close can I build to a drainage ditch or pond in Island County?
Can I connect my roof drain or sump pump straight into the county's stormwater system?
Sources & Official References
Other rules in Island County
Compare Island County to another location·View the Washington environmental rules overview
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