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King County adopts final Cedar River channel migration zone study and map


A new map that shows channel migration zones along the Cedar River has been published by King County.


King County has adopted the final Cedar River Channel Migration Zone (CMZ) study and map, for the area that extends from the river’s mouth in the City of Renton upstream to Landsburg. The final CMZ map is now in effect for the purpose of land-use regulation within King County. Existing land development regulations are not being changed.

Channel migration is when bank erosion occurs and a river channel shifts location. Channel migration zones are mapped and regulated by King County as flood hazard areas. Channel migration zone mapping is required by the Washington State Shoreline Management Act.

A draft Cedar CMZ study and map underwent public review and comment earlier this year, including a public meeting and public comment period. King County Department of Natural Resources and Parks responded to all comments and made minor revisions to finalize the CMZ study and map.

The final Cedar River CMZ map becomes effective June 18, 30 days after adoption by the King County Department of Permitting and Environmental Review. 

The Cedar CMZ study and map, the amendment to the channel migration public rule, and general information about channel migration in King County can be viewed at:

Paper copies are available for review during business hours at the following locations:
• King County Department of Development and Environmental Review, 35030 SE Douglas St., Suite 210, Snoqualmie;
• Fairwood Library, 17009 140th Ave. SE, Renton; and
• Maple Valley Library, 21844 SE 248th St., Maple Valley.
In addition to regulating land use within affected areas of unincorporated King County, the Cedar CMZ map and study will inform the Cedar River Corridor Planning process which can also be viewed at

For more information about the Cedar River CMZ study or map, contact Terry Butler at 206-477-4660, or If you have questions about the King County channel migration public rule or CMZ regulations, contact Steve Bottheim at 206-477-0372 or