Modelling of cantilever bank failure for peat-type meander bends in the source region of the Yellow River

Abstract

Bank retreat involving a combination of fluvial erosion and bank collapse has been found to be a major contributor to sediment transport, lateral migration, and planform evolution of meandering rivers. Previous studies have largely examined the general mechanism of cantilever bank failure. However, the composite process of beam (toppling) failure caused by shear failure of the lower part composed of non-cohesive soil remains poorly understood. The current paper investigates the diversity and coupling of this collapse process, which is the dominant pattern in the peat-type meandering rivers of the Zoige River basin in the source region of the Yellow River. For this purpose, morphologic and hydraulic measurements were done in the summers of 2016 and 2017. Moreover, a combined method of a theoretical model and numerical simulation was developed to be applied for a continuous meandering channel in the Zoige basin, focusing in particular on five typical cross sections of a highly convoluted bend approaching neck cutoff. Specifically, the theoretical model evaluating the stability of overhanging riverbank was based on static equilibrium theory considering the interaction between composite soil layers. In addition, the Bank Stability and Toe Erosion Model was used to simulate the retreat process of the silt layer based on field measurements including bank morphology, soil composition, and hydrological parameters. Thus, a calculation method for the occurrence of cantilever beam failure in the flood period is proposed, and temporal change and spatial variability in bank profiles caused by three consecutive failures is estimated at the five sections. Satisfactory results showed a relatively close agreement between the calculations and field measurements in terms of the width of the overhanging arms and the dimensions of the slump blocks.