Experimental study on the bank erosion and interaction with near-bank bed evolution due to fluvial hydraulic force

Bank erosion is a typical process of lateral channel migration, which is accompanied by vertical bed evolution. As a main sediment source, the failed bank soil may directly cause the increase of sediment concentration and considerable channel evolution in a short time. The paper presents an experimental study on non-cohesive and cohesive homogenous bank failure processes, influence of the failed bank soil on bank re-collapse, as well as the interaction between bank failure and near-bank bed evolution due to fluvial hydraulic force. A series of experiments were carried out in a 180 degrees bend rectangular flume. The results reveal the iteration cycle between bank erosion and bed deformation: undercutting of the riverbank, slip failure of the submerged zone of the bank, as well as cantilever failure of the overhang, failed bank soil staying at bank toe temporarily or hydraulic transportation, exchange between the failed bank soil and bed material, bed material load being re-transported either as bed load or as suspended load, and bed deformation. Same as bank failure, the mixing of failed bank soil and bed material is more severe near the curved flow apex. Moreover, non-cohesive bank failure tends to occur near the water surface while cohesive bank failure near the bank toe. For non-cohesive dense (sandy) soil, the bank erosion amount and residual amount of failed bank soil on the bed increase with the near-bank velocity or bed erodibility. But for cohesive soil, only bank erosion amount follows the above rule. The results are expected to provide theoretical basis for river management and flood prevention.