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Opportunity for public comment on study of the Greenwater River channel migration zone and public rule


Natural Resources and Parks
Public Affairs

Opportunity for public comment on study of the Greenwater River channel migration zone and public rule


A public meeting has been scheduled for Nov. 16 to view draft maps and ask questions about a 1.2-mile channel migration zone and hazard-area regulations along the Greenwater River. King County staff will be available to answer questions about the study and permitting regulations.


King County, as the service provider for thersz_kcfcd_21 King County Flood Control District, has issued a draft study of the Greenwater River’s channel migration zone (CMZ) which maps areas considered at risk of flood-related hazards due to natural changes in the river’s location.

A virtual public meeting to discuss the migration zone and impacts to property owners will take place on Tuesday, Nov. 16 from 6-8 p.m. To learn more about the draft study and map, provide comments, and register for the virtual public meeting, visit

A CMZ is mapped and regulated by King County as a type of flood hazard. The natural movement of a river across its floodplain can occur over time – either gradually, due to erosion on one bank and sometimes matched by sediment deposition on the opposite bank; or suddenly, when a channel jumps its bank into a new location. 

This study identifies areas potentially at risk of channel migration along 1.2 miles of the Greenwater River, starting from the confluence with the White River upstream to a private bridge crossing.

“Our understanding of past and potential future river movement is bolstered by Light Detection and Ranging imagery that ‘sees’ through vegetation and greatly improves our mapping of past and likely future hazards,” said Josh Baldi, Director of King County’s Water and Land Resources Division.

“This draft mapping and the proposed public rule under review recognize the reality that rivers don’t stay in one place; in areas like Greenwater, the channel can rapidly change course,” said John Taylor, Director, King County Department of Local Services. “This mapping helps us to keep the community informed about hazards and plan for future actions to reduce risk to the community.”

A 45-day public comment period for the draft CMZ study and accompanying map begins Nov. 16. Once finalized and incorporated by amendment into King County’s CMZ Public Rule, new land development applications within the CMZ will be subject to the County’s existing zoning code regulations.

The Nov. 16 virtual public meeting will give participants a chance to learn more about the CMZ along the Greenwater River and hazard-area regulations and comment on the draft report and map. The draft CMZ documents may be revised based on comments received during the meeting and associated comment period.

A final Greenwater River CMZ map will be adopted by the King County Department of Local Services. In addition to regulating new land development within affected areas, the Greenwater River CMZ map and study may inform implementation of flood-risk reduction programs and capital projects.

Printed copies of the draft study and maps can also be reviewed at the Enumclaw Public Library at 1700 1st St., Enumclaw.

For more information about the draft Greenwater River CMZ study, map, or public meeting, contact Judi Radloff, project manager and geologist, King County Department of Natural Resources and Parks, at 206-263-6844 or

For those with questions about the King County Channel Migration Public Rule or CMZ regulations, contact Jim Chan, Permitting Division Director, King County Department of Local Services, at 206-477-0385 or

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The King County Flood Control District is a special purpose government created to provide funding and policy oversight for flood protection projects and programs in King County. The Flood Control District’s Board is composed of the members of the King County Council. The Water and Land Resources Division of the King County Department of Natural Resources and Parks implements the approved flood protection projects and programs. Information is available at

King County Department of Local Services works to promote the well-being of residents and communities in unincorporated King County by seeking to understand their needs and delivering responsive local government services. Local Services maintains county roads and bridges, issues permits, manages land use planning, and provides many other services to unincorporated areas. Learn more at