Seixas, G. and Veldhuisen C., 2019. Forest practices and regulatory Channel Migration Zones in the Skagit River Basin since the Forests and fish Report. Skagit River System Cooperative, La Conner, WA. pp. 30.

In Washington State, riparian corridors along fish-bearing streams are protected from forest practices (primarily logging and road construction) in the Washington Forest Practices Rule (Washington Administrative Code 222) to provide ongoing ecological functions despite management activities on adjacent lands. River reaches that show potential for migration across their floodplains or erosion into adjacent hillslopes face additional restrictions to preserve riparian function despite future shifts in river position. (Alluvial fans also receive Channel Migration Zone (CMZ) protections; this report is focused on CMZs in post-glacial valley bottom environments, not alluvial fans.) Since the Forests and Fish Report (U.S.F.W.S. et al., 1999) and the 2001 revision of the Forest Practices Rules (WFPB, 2001), CMZs have been protected to ensure timber management does not diminish riparian processes critical to the maintenance of aquatic ecosystems such as supplying wood to stream channels and providing streamside shade.
Channel Migration Zones are defined as “the area where the active channel of a stream is prone to move and this results in a potential near-term loss of riparian function and associated habitat adjacent to the stream, except as modified by a permanent levee or dike. For this purpose, near-term means the time scale required to grow a mature forest” (WAC 222-16-010). The regulatory definition of ‘near-term’ is 140 years. Due to the possible erosion of the channel banks or avulsion of the stream into adjacent areas (Fig. 1), land managers are required to begin their riparian buffers at the outer edge of the CMZ, not at the channel margin in its current location (WFPB, 2004). However, predicting a river’s future position is challenging given the complex interactions between discharge, sediment supply, and large wood common to alluvial rivers (Abbe and Montgomery, 2003; Brummer et al., 2006). Therefore, CMZ delineation relies upon empirical data from available historical aerial photographs, topographic data, and field observations.