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Broad Level Channel Stability Assessment

The following analysis identifies general associations of stability, rather than a site-specific field measurement approach (i.e., as implemented in PLA). This approach can identify river reaches that are typically not indicative of stability/sediment problems. Delineation of stream types helps to make interpretations by association that normally would require a more detailed assessment. For example if a stream was described as a gravel-bed stream, and a question arose as to the response of this stream to increased flow…there is a big difference between a B4 versus an F4 or G4 stream type (all being gravel-bed streams). Thus, the interpretations of flow-related impacts, vegetation controlling influence, recovery potential and sediment supply, vary their influence on streams by the nature of the stream themselves. The risk rating system utilized in RRISSC relies on an understanding of differential response to imposed change.

Due to their great complexity, an individual could spend a great amount of time and effort running bedload transport equations and doing factor of safety analysis on streambanks, when the potential for instability and/or disproportionate sediment supply problems may be minimal. The use of these rapid assessment methods are not designed to overlook problems, but rather to isolate those stream types with poor conditions and other variables that may be observed in a consistent, objective, and hopefully, reproducible manner. When in doubt, one may advance to PLA to decrease the level of uncertainty.

The following steps (13 through 19) specifically look at potential risk of channel source sediment and channel stability.

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