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A public meeting was held on May 8, 2017 to discuss the Draft Tolt River Channel Migration Zone study and map.

King County has completed a Draft Tolt River Channel Migration Zone (CMZ) study and map which are now available for public review and comment. Existing regulations are not being changed.

The purpose of the Tolt CMZ study and map is to identify areas along the Tolt River from River Mile 6 to the river's confluence with the Snoqualmie River in the City of Carnation (River Mile 0) considered at risk due to natural changes in the river’s location. Channel migration is the process in which a river moves across its floodplain either by steady progressive erosion or by suddenly switching to a new course. Channel migration is a type of river hazard, different from inundation hazards. (Visit the channel migration page for more information.)

Following are links to the draft map and the draft study and map. (Please visit our Acrobat Help page for help with Acrobat.)

Paper copies are available for review at the following two locations:

Public involvement

Public meeting: King County hosted a public meeting in Carnation on May 8, 2017, to present the draft Tolt River CMZ study and map, describe the proposed amendment of the public rule, and answer questions.          

Public comment: The deadline for comments is May 31, 2017. Written and oral comments may be provided during the public meeting. Written comments may also be emailed to John Bethel at or mailed to him at:
    Attn: John Bethel
    King County Department of Natural Resources and Parks
    201 South Jackson Street, Suite 600, Seattle, WA 98104

CMZ map preparation and adoption process

The draft CMZ report and map may be revised based on comments received. A final Tolt River CMZ map will be adopted by the Department of Permitting and Environmental Review under authority of the King County Code 2.98, 21A.02, and 21A.24. Once adopted, the Tolt CMZ study and map will be used to regulate land use within affected areas and may inform implementation of Tolt River riverine risk reduction projects. 

The draft Tolt 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).

Effects of CMZ mapping on land use

The Tolt River CMZ map will be used to regulate land use within the mapped CMZ. For example, new development generally is not allowed within the channel migration zone mapped as a severe hazard area, and new development may be restricted within the channel migration zone mapped as a moderate hazard area. These are existing land use regulations that are not being revised due to this Tolt CMZ study and map. Visit the channel migration zone page for more information.



For more information about the draft Tolt CMZ study and map or channel migration mapping methods, please contact John Bethel, 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 Steve Bottheim, Department of Permitting and Environmental Review.