ABSTRACT
Riverbank erosion is an important source of sediment production and remobilization in rivers. This phenomenon plays a key role in floodplain development and water resources management. Composite riverbanks, typically consist of a cohesionless erodible material overlain by a less erodible layer of finer material, are widely observed on rivers flowing through alluvial deposits. Fluvial entrainment or seepage erosion of the erodible material from the lower bank usually occurs at a much higher rate than erosion of the less erodible material from the upper cohesive bank. This leads to the formation of a cantilevered (overhanging) bank profile, with upper bank retreat taking place predominantly by the failure of these cantilevers. The Kordan River in Iran is one example of a riverbank which is experiencing excessive erosion and bank retreat through cantilever type failure. In this research, to clarify the importance of the various parameters affecting the stability of composite riverbanks, the impacts of independent parameters affecting the stability of cantilever banks are evaluated in a series of model sensitivity analyses using a new model of riverbank stability analysis. In this paper, shear-type failures are analyzed using a recent proposed bank stability relation that considers the hydrological status of cantilevered riverbanks, while beam-type failures are analyzed using a previously proposed relation. The results show that care should be taken when estimating the values of (i) geometrical shape of the overhanging-block and (ii) bank material cohesion and unit weight, as predictions of bank stability are sensitive to variations of these factors. Conversely, a cruder estimation of the soil internal friction angle (except for beam-type), matric suction angle, flow depth, and ground water level, may still provide a reasonable degree of accuracy in the bank stability analysis.
