Middle White River Channel Migration Zone study and map
Final Map and Public Rule
The Middle White River Channel Migration Zone (CMZ) study and map were completed in 2019. The amended channel migration public rule became effective December 25, 2019. Following are links to the final map, related study, and amended channel migration public rule (please visit our Acrobat Help page for help with Acrobat).
- 2019 Middle White River channel migration zone map (1.23 MB, PDF)
- 2019 Middle White River channel migration study and map (55.5 MB, 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 for review at the following two locations:
- King County Department of Local Services – Permitting Division, 35030 SE Douglas Street, Suite 210, Snoqualmie.
- Enumclaw Library, 1700 1st Street, Enumclaw, WA (external link).
The purpose of the Middle White River CMZ study and map, adopted November 25, 2019, is to identify areas along the White River from Mud Mountain Dam to downstream of the State Route 410 bridge crossing which are at risk from channel migration hazards. Channel migration is a natural process that occurs as a river slowly moves across the floodplain or rapidly shifts into a different location. Using historic information, a CMZ is the area in which the river channel is predicted to move over time. Channel migration is a type of flood hazard, different from inundation (floodwater) hazards (visit the channel migration page for more information).
The Middle White River 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.
CMZ map preparation
The Middle White River 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 Code 2.98, 21A.02, and 21A.24. CMZ mapping is required by the Washington State Shoreline Management Act.
The draft Middle White River CMZ study and map underwent public review in 2019. Public comments were considered in finalizing the CMZ study and map. The public review and adoption timeline follow:
- August 20, 2019: King County hosted a public meeting in Enumclaw attended by 12 people. King County staff presented the draft Middle White River CMZ study and maps and described the channel migration public rule amendment process by which the CMZ map is adopted.
- October 6, 2019: 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.
- November 25, 2019: Final Middle White River CMZ map adopted by the King County Department of Local Services by amending the existing channel migration public rule.
- December 25, 2019: Final Middle White 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 development of the draft Middle White River CMZ study and map or channel migration mapping methods, please contact Judi Radloff, Geologist, 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.