Channel Migration Assessment

Steps 3-5 – Analysis (Steps 3- 5 describe the sequence of tasks for mapping channel migration zones, assessing processes, and identifying hazards.)

Step 3: Determine channel reach breaks for channel migration analyses

Product: Descriptions and maps locating the channel migration zone as required by the SMA for the inventory and watershed characterization phase of the SMP update or for developing comprehensive flood hazard reduction plans.

At this point, we assume that you have expertise to conduct the assessment, or will be contracting the expertise and those persons will have an understanding of the methods that were previously described in the general assessment protocols (Table 4). Step 4 applies to all methods that are looking at some level of historic and current map and aerial photo comparison.

Change in channel confinement, gradient, pattern (Step 1b), geologic constraints, man-made constraints (bridges, dams etc) (Step 1a), stream confluences, land use and zoning and other factors deemed relevant are used to determine reach breaks. Reach characteristics should be included in the report, for example in Pierce County CMZ report (pdf).

Maps (USGS 7.5’ topographic maps) and remote sensing data (aerial photographs, orthophotos, DEM, LIDAR) provide additional information to assist in selecting channel reach breaks by confinement, gradient, and channel pattern. Land cover maps may provide information on bedrock outcrops. Geology (WDNR geology site) and soil maps may indicate the erodibility of formations. [Note the WDNR geology maps are large resolution and won’t identify features the may cause local control].

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