Skip to main content
The Third Avenue entrance to the King County Courthouse is temporarily closed. Please use the Fourth Avenue entrance.  
King County logo

Following are links to the final map, the final study and map, and the amended channel migration public rule effective June 18, 2015. (Please visit our Acrobat Help page for help with Acrobat.)

Paper copies are available at the following three locations:

  1. King County Department of Local Services, Permitting Division, 35030 SE Douglas Street, Suite 210, Snoqualmie.
  2. Fairwood Library, 17009 140th Avenue SE, Renton (external link).
  3. Maple Valley Library, 21844 SE 248th Street, Maple Valley (external link).


Channel migration is the lateral or downstream shifting of a river channel within its river valley. Channel migration is a type of flood hazard, different from inundation hazard. Visit the channel migration page for more information.

The Cedar River Channel Migration Zone (CMZ) Study and Map, effective June 18, 2015, applies to the Cedar River valley from Landsburg (river mile 22) to the river mouth in Renton (river mile 0). The Cedar CMZ Study and Map are used to regulate land use within affected areas, identify hazard areas, and help property owners make informed land use decisions.

New development generally is not allowed within the severe hazard area of the channel migration zone and new development may be restricted within the moderate hazard area of the channel migration zone.

The Cedar CMZ Study and Map also will be used to inform the Cedar River Corridor Planning process.

CMZ map preparation

The Cedar CMZ study and map were prepared using CMZ mapping methods specified in the King County Channel Migration Zone Public Rule, consistent with policies in the King County Flood Hazard Management Plan, Washington State Shoreline Management Act (external link), and the Washington State Department of Ecology Channel Migration Assessment (external link)

Map adoption process and public involvement

CMZ maps are adopted by amendment to the King County channel migration public rule under authority of the King County Codes 2.98, 21A.02, and 21A.24. Channel migration zone mapping is required by the Washington State Shoreline Management Act.

The draft Cedar CMZ study and map underwent public review in 2015. Public comments were considered in finalization of the CMZ study and map. 

  • Feb. 4, 2015: King County hosted a public meeting attended by more than 60 people. King County staff presented the draft Cedar CMZ study and map and described the channel migration public rule amendment process by which the CMZ map is adopted. There was a question and answer period and the CMZ map was on display.
  • March 23, 2015: The public comment period closed. King County Department of Natural Resources and Parks responded to all comments and made minor revisions to the draft CMZ study and map.
  • May 18, 2015: Final Cedar River CMZ map was adopted by the King County Department of Permitting and Environmental Review by amending the existing channel migration public rule.
  • June 18, 2015: Final Cedar CMZ map became effective, 30 days after adoption.

For more information about the draft Cedar CMZ study and map or channel migration mapping methods, please contact Jeanne Stypula, Managing Engineer, River and floodplain Management Section, Water and Land Resources DivisionDepartment of Natural Resources and Parks.

For more information about King County’s existing land use regulations in channel migration zones, please contact Steve Bottheim, Department of Permitting and Environmental Review.