Overhanging failure is a major problem in river morphology, and it affects the riverbank geometry. Several studies have investigated different types of riverbank failure; however, uncertainty remains regarding to the process of overhanging failure. We carried out experiments on the mechanism of overhanging failure by using three types of cohesive materials classified by the percentage of silt-clay content. The experiments showed that the dominant factor in the failure process was hydraulic erosion in the initial stage. After that, tension cracks developed in the upper surface of banks and beam failure occurred afterward. Furthermore, we developed a numerical model for overhanging failure that uses a triple-grid approach to simulate overhanging behavior within the framework of hydraulic erosion and overhanging failure. The simulated results showed good agreement with the experimental results in terms of the spatially averaged bank width and water level along the bank.