A numerical model is presented for the prediction of ¯oodplain inundation extents, ¯ow depths and velocities, and patterns of suspended sediment dispersion and deposition. The model employs a simpli®ed and novel treatment of ¯uid ¯ow and a conventional convection±diusion mass balance relationship for suspended sediment transport and deposition. These relationships are solved over a ®nite dierence grid with a relatively ®ne nodal spacing, which enables a detailed representation of complex ¯oodplain topography. The model is applied to a 600 m reach of the River Culm, Devon, UK. Continuous records of river stage and suspended sediment concentration monitored at the upstream boundary of the study reach provide the data needed to operate the model. These data are supplemented by measurements of the in situ settling characteristics of the suspended sediment load. Model predictions of overbank ¯ow depths and velocities and patterns of suspended sediment concentrations and deposition amounts are presented. Predicted patterns of overbank deposition are described and compared with ®eld measurements obtained with the aid of astroturf sedimentation traps. Grain size distributions obtained for samples of deposited sediment retrieved from the sedimentation traps are also examined and compared with model predictions. The results of both the ®eld measurement programme and modelling work are shown to have signi®cant implications for the representation of ¯oodplain topography and suspended sediment particle size and settling properties in numerical simulations of overbank processes.