Sediment transport is movement of solid particles with the fluid. It occurs, when water velocities are higher than the critical velocities for the chosen type of river-bed material, In this case the solid particles enter into motion, while deposition occurs when water velocities decrease, There are two approaches to sediment transport modelling: the single-fraction and the multi-fraction approach. The single-fraction approach treats the bed-material as a wholeness, while with the multi-fraction approach the material is divided into several factions, each faction being treated separately. In this work we describe the principle of the single-fraction sediment transport model PCFLOW3D and review the existing multi fraction models. We created a simple MS Excel-based multi-fraction model for predicting sediment deposition. In this model we used two multi-fraction approaches, which differ in the initial number of fractions and the principle of evaluation of contribution of each fraction. The results of both multi-fraction approaches were compared to each other and to the results of the single-fraction model. The differences between the multi-fraction approaches were significant; therefore, we cannot propose adequate equations for upgrading the PCFLOW3D model without adequate measurements that are proposed in this work. Nevertheless, we were able to suggest the necessary changes in the PCFLOW3D model for upgrading the model with the multi-fraction sediment transport approach.
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