Can the rate of wash load be predicted from the bed‐load function?

There exist two types of sediment load, one that bears a certain relationship with the discharge (bed‐material load), and the other which does not (wash load). The result of flume study indicates that the transport rate of wash load, just as that of the bed‐material load, can be calculated according to the Einstein bed‐load function if the instantaneous bed composition is known. On the other hand, the bed‐material load is equally available in the entire bed, but only the surface bed layer contains any significant amount of wash‐load material. Any change of flow or of sediment supply may immediately change the composition of the wash‐load material in the bed. The bed composition as determined from the instantaneous condition of the channel has no lasting significance so far as the wash load is concerned, and this makes the prediction of the wash‐load rate from the bed‐load function impossible.