This experimental study is about the bed-load transport over inlet sills of longitudinal training walls. The focus is on the flow structures around the inlet: the shape, the processes and the effect on sediment transport. Groynes have been replaced by longitudinal training walls in an 11-km long pilot project to optimize training of the river Waal in the Netherlands. These training walls have many advantages, making it worth exploring the performance of these new river training structures further. The inlet sill affects the discharge and sediment transport distribution and hence the morphological stability of the system. However, currently operational morphodynamic models cannot reliably compute the sediment flux from the main channel towards the sheltered side channel behind the longitudinal training wall. Therefore, the research aim was to develop a description of the sediment transport over the inlet sill of these longitudinal walls for implementation in two-dimensional depth-averaged river models. Since knowledge on the flow structures and validation data lacked, a series of flume experiments with the inlet area has been performed. This study shows that the blocking effect due to the sill that functions as obstacle is dominant at the upstream side of the inlet and helical flow due to curvature at the downstream side of the inlet are the dominant three-dimensional flow structures at the upstream side of the sill. Further research is needed for the identification of the shape of the flow structure due to blocking.