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If you own property in unincorporated King County, you are required to maintain any privately owned stormwater drainage facilities on that property. Drainage refers to flow control and treatment facilities, and any conveyances to, between, and from the facilities. Maintenance is required to ensure that these remain effective at protecting the environment and properties as intended.

How to inspect your stormwater facility/facilities

For questions about inspecting your facilities, email us at stormwater@kingcounty.gov or call us at 206-477-4811.

Stormwater drainage facility maintenance checklist

Owners of commercial and multifamily residential properties with privately maintained drainage and stormwater facilities receiving a stormwater fee reduction use this drainage facility checklist:

Drainage Maintenance Standards

Appendix A of the King County Surface Water Design Manual (SWDM) gives information on the county's maintenance standards for drainage facilities.

The Appendix entries are brief and formal. For more detail on maintenance, go to Washington State Department of Ecology's instructions in their:

Note that the King County SWDM makes a distinction between engineered facilities that require maintenance per Appendix A, and non-engineered best management practices (BMPs); whereas Ecology's SWMMWW naming convention refers to both facilities and best management practices as BMPs.

For example, Ecology's 2019 SWMMWW calls detention ponds "BMP D.1"; but despite the 'BMP' designation, this is an engineered facility, comparable to 2021 SWDM Section 5.1.1 detention ponds.

For questions regarding the content of this web page, please contact us at stormwater@kingcounty.gov