Studies of the flow and sediment movement in a cavity with free surface were mostly limited to physical modeling experiments. In this study, the sediment movement is characterized in detail using a 3-D turbulent numerical model. To close the Reynolds equations, the standard k-ε model is employed. The VOF method is adopted to capture the time varying free surface and the porosity method is introduced to deal with the irregular boundary and the varying bed deformation. The computation results agree well with the experimental data in major aspects such as the vertical distribution of the sediment concentration and the deposition topography in the cavity. The comparisons show that this model can well predict the flow structure and the sediment movement and also the river bed deformation in a cavity. Studies of the flow and sediment movement in a cavity with free surfaces were mostly limited to physical modeling experiments. In this study, the sediment movement is characterized in detail using a 3-D turbulent numerical model. To close the Reynolds equations, the standard k The computational results agree well with the experimental data in major aspects such as as the vertical distribution of the sediment concentration and the deposition topography in the cavity. The comparisons show that this model can well predict the flow structure and the sediment movement and also the river bed deformation in a cavity.