Channel Migration Assessment

Step 2c: Choose appropriate approach and method based on planning and management objectives and level of effort

A matrix based on level of effort determined in Step 2b, spatial scale, channel pattern, and channel migration assessment objectives provides guidance on recommended minimum standards of practice (see below).

The numbers in Figure 13 refer to a summary of the approaches. The minimum standard of practice for all levels includes a historical perspective of conditions and disturbances to lend context to present channel stability, mapping the probable or measured CMZ, description of limitations to method used, and level of certainty (see reach break examples (pdf file).

The limitation description should also include limitations for regulating development in CMZ. For example, a basin or watershed scale assessment may not be as rigorous as a reach scale assessment. For regulatory purposes, the basin scale assessment may require a more detailed analysis for property development.

Predicting channel migration requires consideration of both local and system-wide factors. Municipalities may have only short reaches of stream. However, upstream actions have to be considered in relation to potential channel response within their jurisdiction. Moreover, proposed land use changes and restoration projects within the jurisdiction boundaries, including removal of existing structures such as levees or dikes, may affect reaches downstream of the jurisdiction boundaries. Accordingly, upstream and downstream channel reaches should be included and channel response determined in the analysis. The geomorphic description for the South Prairie Creek Channel Migration Assessment in Pierce County provides an example of channel response.

Figure 13: Matrix cross-references channel migration assessments by scale (basin, reach, site), management objectives, level of effort, and channel pattern—M=meandered pattern, B=braided pattern, A=island braided pattern, W= wandering pattern. The method identification numbers refer to the summary of the approaches and methods (Table 4).

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