Sediment Transport Over Fractured Bedrock in a River Bend: A Hybrid Modelling Approach

The modelling of sediment transport over fractured bedrocks in a river bend is a very challenging task. In order to better understand these processes and to develop river training measures to reduce sediment deposition within the navigation channel, a hybrid modelling approach was chosen. This consists of a laboratory scale model with a partially movable bed and a three-dimensional hydro-numerical model. In the scale model sediment particles with low density were used to model the sediment transport. An extensive database with data from nature was available for setting up the two models. In order to determine the transport path of the sediment across the bed, extensive investigations were carried out in the laboratory model at different discharges. The comparison with the near-bottom streamlines in the 3-D model shows that the sediment particles very strongly follow the near-bottom flow over the bedrock. The transport path of the sediment was also confirmed by comparison with a high-resolution digital terrain model where the transport path was estimated from the dominant dunes. The results show a very good representation of the near-bottom flow in the three-dimensional hydro-numerical model. The model is therefore very well suited for the design of river training measures to influence the sediment pathways in order to reduce landfalls in the navigation channel, even if the bedload transport is not directly represented. The hybrid modelling approach has proven to be very powerful, both in terms of the ability to investigate a large number of measures and in terms of the accuracy of the results for physically extremely complex processes.