Unified View of Wash Load and Bed Material Load

Abstract

This paper presents a new generalized model of flow-sediment interaction. The behavior of the wash load and of the suspended bed-material load can then result as special cases of the new model. The latter follows the lines of Einstein’s original probabilistic model except that interparticle forces of mechanical and physico-chemical nature have been introduced and that the flow-induced forces on the individual grains or flocs were assumed to have an upper and lower bound. It is shown that the actual wash load may consist of two distinct types of sediment which may coexist: (a)Bed load function for a limited range of flow conditions whereas above that range it behaves as a wash load; and (b)the other never has a bed load function. It is shown that the latter consists predominantly of silt and clay, i.e., of sediment finer than 0.06 mm, a fact consistently observed in alluvial channels.