In 2019, a 5 million m³ sand nourishment was placed at the Ameland ebb-tidal delta. This pilot nourishment aimed to investigate the feasibility and effectiveness of ebb-tidal delta nourishments and to understand the dynamics in this system. To assess how this nourishment has dispersed through the ebb-tidal delta system, SedTRAILS was used. SedTRAILS is a particle-based sediment transport model currently in development. A new process for interaction with the bed and burial of sediment was recently added to the model. The impact of this process on dispersal and sediment pathways needed to be analysed, as not much is known about the effects of its inclusion on transport and dispersal.

Several schematisations of wave- and tidal forcing were tested. The wave forcing selection had little effect on the overall model results. Storm conditions included in the more detailed schematisation were underrepresented in the model results. The implementation of wave-driven bed velocity had little influence on result as well due to small magnitudes that were calculated for this. A significant difference was found between using a morphological tide and an artificial spring-neap tidal cycle however, requiring further investigation.

Investigation of the burial formulation gave insight into the response of the model to changes in the different parameters. Direct dependence of erosion probability on deposition probability presents a major limitation in the current implementation of burial. Additionally, deposition probability in its current form is positively dependent on the maximum bed shear stress. Inclusion of burial does provide significant room for calibration of results.

Through modelling these various configurations of SedTRAILS, results consistently showed a recirculation of sediment from the nourishment on the ebb-tidal delta together with bypassing around the edge of the ebb-tidal delta, as seen in Figure 1. However, the degree to which bypassing occurs depends heavily on the chosen burial configuration. The bypassing is largely a result of flow around the periphery of the ebb-tidal delta and differs from known bar migration and shoal attachment pathways. Transport into the Wadden Sea basin was not found, likely due to the underestimation of influence of storm conditions.

To improve dispersal modelling with SedTRAILS, the impact of storm conditions needs to be more accurately included in the model. An under-representation of energetic wave conditions leads to a consistent underestimation of wave-related transport. Additionally, more investigation into the effects of the spring-neap tidal cycle is required. The significant difference presented here is an early indication that this is an important factor for SedTRAILS. Validation of dispersal modelled with SedTRAILS can be achieved through quantification of transport, assigning a volume of sediment per particle.

In mid-July 2021, record breaking precipitation fell in Western Europe, causing rivers to overflow their banks. This event has demonstrated that measures are necessary, leading to the JCAR-ATRACE collaboration which brings together multiple hydraulic engineering institutes across Europe to enhance resilience to extreme climate events and fosters long-term research partnerships. This MSc thesis is a contribution to this joint collaboration. The goal of this project was to investigate the potential of detention basins along the Rur river in Germany and optimize their operational strategy to mitigate flood risk near in particular the village of Ophoven, which had suffered from recent floods. A one-dimensional kinematic model was developed of the main river, the floodplains and basins between Jülich and Ophoven. Initially for four basins, the opening times and crest heights of the weirs were sequentially optimized to minimize the peak water height near Ophoven for the 1/100 years flood event. The predictions of the 1D model were verified against the HydroAS2D model which solves the 2D shallow water equations. The optimization revealed that the chosen volumes of the four basins were too small. A method to estimate the required storage volume for a desired downstream peak water height reduction was applied. Then a much larger basin, close to Jülich, was considered. It was found that apart from choosing the appropriate opening time and crest height, not only the storage volume but also the width of the inlet is important. In addition to optimizing the operation of the weirs, the potential of a basin with an un-operated compound weir with four fixed crests was studied. The crest heights were optimized for the 1/100 flood wave. The optimized compound weir, tested for the small detention basin 1 as an alternative to the operated weir, achieved similar level of peak reduction when optimized for the same flood event. However, when the compound weir is applied to another flood event, it can become ineffective. The operated weir is more flexible, but requires that the upstream hydrograph is measured at sufficiently large distance from the basin.