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Sediment Calculation Procedures. Changes are predicted in sediment supply increase (load) and competence of sediment transport utilizing data from stream bank erosion (Step 9), flow related sediment increase (Step 17), total introduced sediment from hillslope process (Step 21) and the entrainment/competence calculations (Step 22). The following categories are predicted in this procedural step:
- Sediment competence calculations for changes in sediment size and/or change in channel characteristics.
- Sediment capacity calculations. Total annual suspended and bedload sediment yield calculations for pre and post treatment stream flow changes. (Flow related increase in sediment). Sediment supply changes.
- Changes in bedload transport due to changes in channel dimension, pattern and profile, stream power/transport relations.
Sediment transport competence and capacity are compared to available particle size and load. Sediment transport computations using various model options such as the Bagnold equation, FLOWSED, and POWERSED, are used for both reference and impaired conditions. The determination of the largest particle size made available from the introduced sediment sources is compared to the competence of the existing channel to accommodate the sediment. This is a critical step in the analytical process, as it determines potential aggradation or degradation. The procedure is similar to previous steps, but uses the output of the changes in introduced sediment and changes in energy (flow and hydraulics due to channel change).
The results from this step will quantify potential sediment transport conditions related to aggradation based on changes in energy and/or changes in supply or particle size. Departure from reference condition for excess sediment/aggradation is documented at this step. The variables used to predict stream channel stability at this stage are summarized in Flowchart 13.
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