Equilibrium state of river bed with three grain size groups of sediment

The objective of this study is to clarify the mechanism of the sediment transport in a reach of the river whose bed is composed of an extremely wide range of the grain size. In this study, we assumed that the bed was composed of three grain size groups of sediment: the larger stones which cannot move at all, the medium gravels which move as bed load, and the finer sand or silt which moves as suspended load. Fundamental experiments were conducted by changing the condition of bed shear stress and the sediment composition of bed. Static equilibrium state of bed was focused on. It was found in the void space of the larger stones that the vertical sorting of sediment occurs clearly. The influence of the arrangement of the larger stone was also investigated. As a result, it was concluded that the effect of the arrangement can be neglected.