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The objective of this step is to convert reference suspended and bedload sediment rating curves to actual sediment rating curves. It is very important to capture the bankfull discharge and to have several data points to take an average of the flow and sediment values. This is due to the differences for the same discharge that often exist in sediment transport attributable to the high spatial and temporal variability of sediment movement. Field methods and equipment used should follow the procedures outlined in Book 3, Chapter C2 of Field Methods for Measurement of Fluvial Sediment (USGS 1999).
It may be necessary to separate the wash load (silt/clay fraction) from the total suspended sediment load for calculation/interpretation purposes. For channel stability purposes, the silt/clay fraction is not energy limited or hydraulically controlled, and in some settings it can be subtracted from the suspended sediment yield data in the prediction of potential aggradation. This would not be the case, however, if there were concerns over accelerated fine sediment deposition into extremely low gradient streams, deltas, reservoirs, lakes, marshes, tidal freshwater or saltwater estuaries. Colloidal sediments can present problems for impaired waters, thus wash load may also need to be retained in their suspended sediment analyses.
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