Wash load is the material in the system, but not present in appreciable quantities in the bed. SIAM does not apply the standard transport equations to compute a mass balance for wash load materials. Instead, it automatically passes them through the sediment reach. If the wash load threshold drops from one sediment reach to the next adjacent downstream reach, the material in the grain class(es) that is no longer wash load is added to the bedload and subjected to the standard mass balance approach.
A wash load threshold must be set for each sediment reach. The drop down box labeled Wash Load Max Class lists 10 grade classes (clays through sands for the standard grain classes) and their upper bound particle size in mm.