River widening to mitigate river training induced bed erosion: A 1D model approach

The Waal river in the Netherlands is experiencing a bed degradation of 2-3 cm per year. This is most probably the result of river training measures in the past, as well as the construction of dams in the upstream part. Bed degradation causes hindrance for shipping and may lead to groundwater issues in the floodplains. River widening (e.g. by large scale floodplain lowering) affects the slope of the river bed and hence reduces bed degradation. In this study, we analyze the morphological changes as a result of river widening, using a 1D morphological model (with mixed size sediment) with which we performed long-term (100 years) simulations for a long river stretch (order of 100 km) . First results show that the model is able to reflect the changes in slope correctly, but that only river widening itself is not sufficient to stop the degradation. Additional simulations with upstream sediment nourishments show that still substantial volumes are needed to stabilize the bed. These preliminary results may already be used for policy preparations but fine-tuning with a 2D model is necessary, before actual management decisions can be taken.