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Channel Processes: Streambank Erosion Prediction

The complexity of predicting annual streambank erosion rates has limited the application of available models. The factor of safety approach is a detailed, process-specific quantitative prediction of the relative risk of streambank erosion as described by Thorne (1999) and Simon et.al. (1999). The factor of safety approach has many valuable applications, but it may not be applicable in WARSSS due to the detailed data collection requirements and the inability of the model to predict annual streambank erosion rate. A process-integration approach is recommended as an alternative, to provide a linkage for the field practitioner to estimate annual bank erosion (Rosgen 2001a). This method involves collecting field data on streambank characteristics to calculate a bank erosion hazard index (BEHI) and near-bank stress (NBS), then relating the ratings to measured erosion. The advantage of predicting streambank erosion rates is to document and quantify the sediment loading from this source. This is accomplished by multiplying the lateral erosion rate times the bank height times the length of bank associated with a given BEHI and NBS. These values are converted from cubic feet/year to tons/year, then compared to total loads from measured values. Both BEHI and NBS play significant roles in WARSSS field measurement.

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