Cedar River Channel Migration Zone Study and Map
Final Map and Public Rule
The Cedar River Channel Migration Zone (CMZ) study and map were completed and adopted through an amended public rule in June 2015. A smaller portion of this effective mapping was reassessed in 2019, resulting in an adjustment to the mapped hazard areas. The map adjustment has been documented per the public rule 21A-24-279A(B)(3). The amended channel migration public rule became effective December 25, 2019.
Following are links to the adjusted map, 2015 study, 2019 reassessment, and amended channel migration public rule (please visit our Acrobat Help page for help with Acrobat).
- Adjusted Cedar River channel migration zone map panel 5 (605 KB, PDF)
- 2015 Cedar River channel migration study and map (32 MB, PDF)
- 2019 Cedar River CMZ Reassessment Technical Memorandum (836 KB, PDF)
- King County channel migration public rule (144 KB, PDF)
- Appendix B to the King County channel migration public rule (331 KB, PDF)
Paper copies are available at the following three locations:
- King County Department of Local Services, Permitting Division, 35030 SE Douglas Street, Suite 210, Snoqualmie
- Fairwood Library, 17009 140th Avenue SE, Renton (external link).
- 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, and the Cedar River CMZ Reassessment Technical Memorandum, adopted November 25, 2019, applies to the Cedar River valley from Landsburg to the river mouth in Renton. The combined 2019 Cedar CMZ Map will be used to regulate land use within the mapped CMZ, 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 2015 Cedar CMZ Study and Map was also 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. CMZ mapping is required by the Washington State Shoreline Management Act.
The draft Cedar CMZ study and map underwent public review in 2015; the reassessment underwent public review in 2019. Public comments were considered in finalization of the CMZ study and map. The public review and adoption timeline is as follows:
- 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. Minor revisions were made 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 (now Department of Local Services) by amending the existing channel migration public rule.
- June 18, 2015: Final Cedar CMZ map became effective, 30 days after adoption.
- August 21, 2019: King County hosted a public meeting to discuss the reassessment.
- October 6, 2019: The public comment period closed.
- November 25, 2019: Final Cedar River combined 2015 and 2019 reassessment CMZ maps adopted by the King County Department of Local Services by amending the existing channel migration public rule.
- December 25, 2019: Final Cedar River CMZ map became effective, 30 days after adoption.
- King County Channel Migration Zone Public Rule
- King County Flood Hazard Management Plan
- Washington State Shoreline Management Act (external link)
- Washington State Department of Ecology Channel Migration Assessment (external link)
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 Division, Department of Natural Resources and Parks.
For more information about King County’s existing land use regulations in channel migration zones, please contact Department of Local Services, Permitting Division.