Experimental study on the interaction between the hydraulic transport of failed bank soil and near-bank bed evolution

Bank failure is a typical process of lateral channel migration. As a huge sediment source, failed bank soil may directly cause the increase of sediment concentration and considerable channel evolution in a short time. Based on the failure mode of composite river bank, a series of experimental tests in flume was conducted to investigate the processes of disintegration and transportation of a failed bank block at the toe of concave bank, and the interaction between the failed soil, bank stability and bed evolution. Experimental results indicate that a part of disintegrated bank block will be transported to convex bank or downstream, and the amount of the residual part depends on the hydraulic scour force and the properties of bank material. Larger flow shear stresses occur in a local near-bank zone with violent turbulence and higher velocity, especially around the failed block. The shear stress at the near-bank end of the failed block is smaller, as compared with the condition without failed block. The larger the size of the failed block is, the greater the influence on shear stress is. Although the failed block cannot prevent the non-cohesive bank soil from collapsing, the processes of bank failure and bed deposition can be reduced. This reduction is more obvious for a larger failed cohesive bank block. Furthermore, the reduction degree in the rate of bed deposition caused by the failed bank block is much higher than that of the occurrence of bank failure.