Channel Migration Assessment

This web site provides a scientific method of analysis designed to identify channel migration zones (CMZs) based on historic patterns, and hydrologic and geomorphic factors inline with the Shoreline Master Program (SMP) Guidelines. It includes:

What is channel migration?

Channel migration is the process by which a stream moves over time. This important ecosystem process supports a number of ecological functions, including wildlife habitat. Streams migrate across valleys due to a variety of reasons including channel erosion, avulsion, and aggradation.

What is a channel migration zone (CMZ)?

The Shoreline Master Program (SMP) Guidelines define CMZs as including areas within which a river channel can be expected to migrate over time due to hydrologically and geomorphologically related processes.

Why do we need to identify CMZs?

The principal goal of identifying CMAs or delineating the CMZ is to predict areas at risk for future channel erosion due to fluvial processes. CMZ delineations help reduce hazards to human communities by guiding development in and along river systems away from such areas.

Limiting development within CMZs also reduces the costs of repairing or replacing infrastructure and major civil works that might otherwise be threatened or damaged by channel migration. Additionally, CMZ delineations can provide guidance in reducing degradation and loss of critical aquatic and riparian habitats, helping assure that fluvial process are accommodated and that the river landscape is not permanently degraded or disconnected from the river by development.

How will this web site help?

The use of this Channel Migration Assessment, in consultation with Department of Ecology staff, will facilitate successful shoreline planning by cities and counties. This web site is intended to support planning for "shorelines of the state" required by the Shoreline Management Act (SMA).

Identifying the general location of the CMZ is a required part of the shoreline planning process during the inventory and characterization of natural shoreline processes and associated ecological functions.

Additionally, the SMA requires management of CMZs to protect their ecological functions and to reduce potential hazards to human settlements by guiding the development near rivers and streams away from channel migration areas.

The Flood Hazard Reduction section of the SMP Guidelines is specific on what should be considered when identifying CMZs:

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