Abstract: A three-dimensional numerical model based on unstructured triangle grids was used for predicting the flow and time variation of bed deformation in a 180° channel bend. The standard turbulence closed model and explicit project method were employed to solve the RANS equations. The bed load transport quantity was determined with the Van Rijn formula. For a strong secondary flow and the influence of transverse bed slope on the direction of lateral bed load sediment in sharp channel bend, the simple Engelund model was employed to compute the deviation of the sediment transport. Moreover, the critical bed shear stress of incipient motion was also corrected according to the method advanced by Van Rijn. A full set of unsteady flow and bed deformation process within a same time step was predicted. The predicted bed deformation over time was compared with data from a physical model study and good agreement was found.

Key words: channel bend, alluvial channels, secondary flow, transverse slope, unstructured grid