A coupled two-dimensional vertical width-integrated hydrodynamic and sediment transport numerical model is presented to simulate the ''turbidity maximum'' formation and dynamics in the Gironde estuary. A turbulence closure sub-model is used to parametrize the turbulent mixing process. The numerical results of a five-day simulation are compared with field measurements carried out at several locations. The formation and the displacement of the turbidity maximum during one tidal cycle are correctly simulated. The intensity of the ''turbidity maximum'' is strongly related to the turbulent energy field. The influence of the tidal amplitude on the suspended matter transport is also studied during the simulation.