The two-phase approach (fluid-solid) is an interesting one in modelling sediment transport process. This paper presents the application of such a model for simulating watersediment mixed flows in a periodic open channel, for which some experimental data are available. Particularly, the results obtained by the model show the importance of turbulence in the transport process. Thus, a drift velocity, which is due to the correlation between the instantaneous particle distribution and the fluid velocity fluctuations, is introduced. This is necessary to improve the numerical results.