Abstract: Riverbanks with composite materials are commonly found on alluvial rivers. Lateral erosion processes of such banks are very different along the vertical direction. On the basis of three-dimensional (3-D) flow and sediment transport model and mechanisms of riverbank erosion, a 3-D numerical method was developed for simulating bank erosion processes with composite materials using the adaptive grid scheme. The 3-D numerical method is applied to a conceptual meandering channel, and to simulate the variation of 3-D flow structure as erosion of the bank progresses. Results show that the main flow migrates towards the concave bank after the erosion of bank toes, and then, a new secondary flow structure with reverse direction compared to the initial secondary flow structure is formed on the bank toe. The main flow migrates further towards the concave bank after the collapse of upper layers, and the new secondary flow structure on the bank toe disappears. Again, the main flow migrates towards the concave bank after the erosion of bank toes. Thus, the main flow migrates towards the concave bank step by step, resulting in a continue bank erosion and channel migration.