GIS Data Catalog
Channel Migration Areas in King County
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Summary
This dataset can be use to estimate the channel migration for seven rivers: White River, Raging River, Tolt River, Three Forks area of Snoqualmie River, Cedar River, Green River, and the South Fork of the Skykomish River.
Description
Channel migration hazards for seven King County rivers: Middle White River, Raging River, Tolt River, Three Forks area of Snoqualmie River, Cedar River, Green River, and the South Fork of the Skykomish River.
The Cedar River was updated April 2015, the SF Skykomish June 2017, and the Tolt July 2018.
In December 2019, the Middle White River was added, the Raging River was updated, and a revision was made to the updated Cedar CMZ.
The Lower Snoqualmie CMZ was added November 2025 after adoption by the Dept. of Local Services.
Layer information
| Layer Name | chnlmigr_area |
| Subject Category | Hydrography |
| Title | Channel Migration Areas in King County |
| Feature Count | 246 |
| Feature Type | Polygon |
| Next Update | As needed |
| Spatial reference | EPSG:2926 |
| Control ID | 257 |
| Place Keywords | King County, WA, Pacific NW, Washington State |
| Theme Keywords | Rivers, Hydro, Channel, Migration, Inlandwaters |
| Supplemental Information |
There are several rapidly migrating river systems in King County. Studies (cited below) have been prepared by or for the King County Department of Natural Resources to map and describe areas of channel migration hazard on sections of seven King County rivers: middle White River, Raging River, Tolt River, Three Forks area of Snoqualmie River, Cedar River, Green River, and the South Fork of the Skykomish River. In each study, the maximum probable future limits of channel migration were defined using historic meander belt widths and other geomorphic features. Land within these limits is classified according to the relative degree of hazard from channel migration, based upon historic rates of channel migration and the presence of major bank protection structures that protect arterial roads and subdivisions. |
Table Preview
Attribute information
|
OBJECTID
From ESRI |
Description
Internal feature number. DomainSequential unique whole numbers that are automatically generated. |
|
HAZARD
From King County |
Description
Level of channel migration hazard. DomainMODERATE - The moderate hazard area is located between the outer boundary of severe hazard and the maximum probable limits of future migration. POTENTIAL - The area is not yet a channel migration zone, but could become one. SEVERE - The severe hazard area includes the width of the river channel itself plus a width equal to one hundred (100) years times the average annual channel migration rate. It is assumed that channel will migrate for fifty (50) years on both sides of the present channel location during this hundred year period. |
|
SHAPE
From ESRI |
Description
Feature geometry. DomainCoordinates defining the features. |
|
Shape.STArea()
From SQL Server |
Description
Returns the area of a geometry instance in square units, based on the spatial reference identifier (SRID) of the geometry. DomainDouble |
|
Shape.STLength()
From SQL Server |
Description
Returns the total length of the elements in a geometry instance. DomainDouble |
Contact information
| Maintained by | DNRP - Water and Land Resources |
| Primary |
Harkeerat Kang
Harkeerat.Kang@kingcounty.gov |
Terms of Use
| License | Terms of use and copyright |
Use this Data
|
Links
How to use in ArcGIS Pro |
|
| Sharing Status | Public |
Summary
This dataset can be use to estimate the channel migration for seven rivers: White River, Raging River, Tolt River, Three Forks area of Snoqualmie River, Cedar River, Green River, and the South Fork of the Skykomish River.
Description
Channel migration hazards for seven King County rivers: Middle White River, Raging River, Tolt River, Three Forks area of Snoqualmie River, Cedar River, Green River, and the South Fork of the Skykomish River.
The Cedar River was updated April 2015, the SF Skykomish June 2017, and the Tolt July 2018.
In December 2019, the Middle White River was added, the Raging River was updated, and a revision was made to the updated Cedar CMZ.
The Lower Snoqualmie CMZ was added November 2025 after adoption by the Dept. of Local Services.
Contact information
| Maintained by | DNRP - Water and Land Resources |
| Primary |
Harkeerat Kang
Harkeerat.Kang@kingcounty.gov |
Terms of use and copyright
| License | Terms of use and copyright |
Change history
| 11/18/2025 |
The Lower Snoqualmie CMZ was added November 2025 after adoption by the Dept. of Local Services. |
| 12/25/2019 |
The Raging River Channel Migration Zone (CMZ) study and map and Middle White River CMZ were completed in 2019. A smaller portion of the effective Cedar CMZ mapping was reassessed in 2019, resulting in an adjustment to the mapped hazard areas. The amended channel migration public rule became effective December 25, 2019. |
| 7/13/2018 |
The Tolt River CMZ study and map, completed in June 2017, and the January 16, 2018 Reassessment of the King County Channel Migration Zone Mapping near the Holberg Levee, Tolt River (Tolt River CMZ Reassessment Technical Memo) were incorporated into the final July 2018 Tolt River Channel Migration Zone (CMZ) map per 21A-24-279A(B)(3). The amended channel migration public rule became effective July 13, 2018 |
| 9/1/2017 |
The South Fork Skykomish Channel Migration Zone (CMZ) study and map were completed in 2017. The amended channel migration public rule adopting the South Fork Skykomish CMZ became effective in September 2017. |
| 6/15/2015 |
Added Cedar River CMZ data 06/15/2015 Source data 04/15/2015 |