Process of clay bed deformation due to the action of moving particles of bedload

The purpose of this study is to elucidate the effects of sand or gravel transported as bedload on the clay bed deformation and to understand the lateral and vertical structures of the clay bed. It has already found that the bedload plays a role of erosion promotion of clay bed and a mixed layer of deposited sand and clay is formed on the bed surface. This mixed layer prevents from more clay erosion by protecting it from the contact or collision with bedload. As a result, the mixed layer has the suppressing effect of clay erosion. In this study, a series of experiments in two different channels, one is a straight channel and the other is a uniformly curved channel in order to make these two effects clear, and the deformation process of clay bed is revealed. In considering this process, we focused on the mixed layer of sand and clay formed on a bed surface. As a result of this study, the mixed layer is formed in the initial stage around to the central portion of the bed in a straight channel. In case of bed in uniformly curved channel, the layer starts to form in the area close to the inner side wall because of the effect of centrifugal force on bedload. After the mixed layer was formed, the erosion process proceeds gradually in the transverse direction with lateral widening of the mixed layer.