Channel Migration Zone

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Salish Sea References

• Watershed Characterization Mapper
• The Encyclopedia of Puget Sound
• PRISM Project Search
• Washington Coastal Atlas
• WDFW's Salmonscape Map

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"Channel migration zone" is a concept that describes that area of a floodplain landscape which is anticipated to be at risk to future channel erosion over some period of time relevant to decision making. Definition of channel migration zone is used to define risk of damage from bank erosion to human settlements. It has also been used to define an area where reforestation is most likely sustain fish habitat formation as a stream evolves over time.

Notes

• Rapp & Abbe 2003 describes a framework for delineation funded by WDOE.
  • CMZ delineation is a prediction of future processes based on historical and current observations.
  • A CMZ determination must specify a design life.
  • Channel migration zone includes the historical migration zone (largely based on historical maps and photography), an avulsion hazard area (based on observation of topography and vegetation), and an erosion hazard area, which combines an erosion setback (predicted rate of erosion over the time of interest), and where appropriate, a geo-technical setback (a distance beyond the erosion zone necessary to establish a stable slope). Portions of the historical channel migration zone may be disconnected by berms, levees, or causeways.
• CMZ mapping, can with county approval, affect FEMA National Flood Insurance Program and thereby affects the definition of "floodway" and implementation of the NFIP Biological Opinion.
• EPA has provided funding through WDOE for migration zone mapping, the project appears to be led by Ms. Patricia Olson, of the Shorelands and Environmental Assistance Program.
• WDOE offers a page on channel migration assessment.
• Channel migraiton zone mapping is (required?) under Shoreline Master Program updates mandated by the Shoreline Management Act
• A large number of studies are apparent as PDFs through a google search, but it is difficult to find a map based description of existing data.

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