Longitudinal training walls on the Waal River (Netherlands) as a River training alternative

Longitudinal training walls are man-made river dividers. They were built in the Netherlands as a replacement of perpendicular groynes as a river training alternative to decrease flood risk and stop the ongoing bed degradation, while still allowing safe navigation. The efficiency of these structures relies on the long-term stability of the two channels on either side of the walls. Sediment and flow distribution are mainly controlled by a sill that behaves as a side weir at the upstream end of the walls. Research conducted to understand the morphodynamic behavior of these sills concludes that three-dimensional flows are present and that their impact on sediment transport still needs to be investigated. This paper presents the historical events that led to the construction of the longitudinal training walls in the Waal River located in the Netherlands, a literature review of previously conducted research and the questions that still need to be addressed in future research to describe the sediment transport over the sill.