A mathematical model for suspended sediment transport is described, which enables the investigation of certain effects of river works or geometrical changes, or both, in a river or estuary by morphological computations. The model is based on the two-dimensional diffusion-convection equation. This equation describes the distribution of the sediment concentrations in a two-dimensional flow field by diffusion and convection. For the local velocities in the vertical the logarithmic distribution is used, while for the sediment diffusion coefficient a new expression is applied. The diffusion-convection equation is solved by an implicit numerical method using a coordinate transformation, while the influence of the diffusion coefficient on the adaptation of the transport in the case of an overcapacity of sediment is presented. A dimensionless graph of the adaptation length of a uniform concentration vertical is given, the application of the model for tidal flow is described and for such conditions a prototype verification and a sensitivity analysis is given. The model is limited to situations with relatively small changes in lateral direction and nongraded bed.