Seattle, WA Environmental Rules: Stormwater Management (2026)
Key Facts
- Governing section
- SMC 22.805.020, Stormwater Code
- Max civil penalty
- $5,000 per violation per day (SMC 22.808.050)
- Enforcing agencies
- Seattle Public Utilities and SDCI
- Applies to
- All projects, even without full drainage review
- Cross-referenced rules
- Chapters 23.60, 25.06, 25.09 for flood-prone sites
Summary
Seattle's Stormwater Code requires every development project to maintain natural drainage patterns and prevent adverse impacts to receiving waters, under SMC 22.805.020. Discharge points must preserve natural pathways and match downstream drainage capacity. Seattle Public Utilities and the Department of Construction and Inspections jointly enforce the code, and violations draw civil penalties up to $5,000 per day under SMC 22.808.050.
22.805.020 - Minimum requirements for all projects A.Minimum requirements for maintaining natural drainage patterns. For all projects, natural drainage patterns shall be maintained and discharges shall occur at the natural location to the maximum extent feasible and consistent with subsection 22.805.020.B. Drainage water discharged from the site shall not cause a significant adverse impact to receiving waters or down-gradient properties. Drainage water retained or infiltrated on the site shall not cause significant adverse impact to up-gradient or down-gradient properties. B.Minimum requirements for discharge point. The discharge point for drainage water from each site shall be selected using criteria that shall include, but not be limited to, preservation of natural drainage patterns and whether the capacity of the drainage system is adequate for the flow rate and volume.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Municipal Code: Supplement 44 Update 1).
Full Breakdown
020, part of the Stormwater Code (Title 22, Subtitle VIII), sets the baseline drainage-management standard for every construction and land-disturbing project in the city, not just projects big enough to trigger full drainage review. Subsection A requires that natural drainage patterns be maintained and discharges occur at the natural location to the maximum extent feasible; discharged water 'shall not cause a significant adverse impact to receiving waters or down-gradient properties,' and water retained or infiltrated on site must not harm up-gradient or down-gradient neighbors either.
Subsection B controls where a site's discharge point may be located, requiring SPU/SDCI to weigh preservation of natural drainage patterns against whether the receiving drainage system has capacity for the added flow rate and volume; projects that trigger drainage review must show the discharge point on an approved drainage control plan. 09) rules. Subsection D requires a construction stormwater pollution prevention plan for every project, covering marking of clearing limits, retaining topsoil and native vegetation, and other temporary erosion controls, with the Director able to demand additional controls when the baseline measures aren't enough.
807 sets the drainage-review thresholds that determine which projects need a full drainage control plan versus simplified compliance, and the Seattle Stormwater Manual (a joint SPU/SDCI Director's Rule) supplies the technical BMP standards referenced throughout.
Violations & Fines
Stormwater Code violations are enforced under SMC 22.808, which lets the Director assess a civil penalty of up to $5,000 for each violation, with every day a violation continues counted as a separate violation. Penalties are scored against a matrix covering public-health risk, environmental damage, willfulness, and repeat offenses; the Director may instead refer significant-harm cases to the City Attorney to recover the violator's full economic benefit, plus a 15 percent administrative surcharge on any damages owed.
Frequently Asked Questions
Does Seattle's stormwater code apply to small residential projects?
What happens if my project's stormwater discharge harms a neighboring property?
Who enforces Seattle's Stormwater Code?
Sources & Official References
Other rules in Seattle
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Stormwater Management in Nearby Cities
How other cities in King County handle stormwater management.