ABSTRACT This study presents field data for topography change, bed material, water surface elevation and hydrograph in Tan Chau reach in Vietnam to understand mechanism of the river change. These show that bank shifting tends to occur toward anti-clock wise and sand bars migrate downstream, resulting in a much larger bar, which is influenced by co-presence of non-cohesive and cohesive sediment and artificial works. In addition, bed material loads are originated by bank erosion. A 2- D numerical model is proposed to treat such river changes by introducing erosion rate formula for cohesive material and formula for estimating the thickness of sediment transport layer into a usual method. The new method is applied to the study reach which is 15km long and is supposed to be applicable for predicting bed deformation of natural river with fine sediment.
