Heavy rainfall and cross-border dam failure can result in extreme flood waves. Climate change increases the frequency and intensity of extreme rainfall events, which can push hydraulic structures such as dams to their limits. Potential failure can lead to severe flooding that is rarely accounted for in flood risk planning, particularly if the structure in question is located abroad. This study assesses the consequences for the Netherlands of extreme flood waves in the Rur river. To model flood propagation, a new hydrodynamic model was developed, for the Dutch section of the Rur river basin. Several synthetic hydrographs were implemented as upstream boundary condition at the Dutch border. First, two different hydrographs were generated representing extreme flood waves. One with a peak discharge of approximately 900 m3/s and a total cumulative volume of approximately 22 million m³, called the Large Flood Wave (LFW) and one with a peak discharge of 10000 m³/s and a cumulative volume of 143 million m³ named the Massive Flood Wave (MFW). Presenting two different extreme hydrograph scenarios. To see if the shape of the hydrograph results in different outcomes these hydrographs are flattened. Three scenarios per dam are evaluated: the original hydrograph (LFW and MFW 100% peak discharge) and two reduced scenarios where the peak discharge is scaled to 75% and 50% of the maximum peak. The total flood volume remains constant for all scenarios.
Determining direct economic damage. From the Dutch border to Roermond (≈ 19 km) the arrival time of the Large Flood Wave is 22 hours. Due to attenuation across the wide floodplain, the peak discharge is reduced to 161 m/s in Roermond. A sensitivity analysis indicated that increasing the initial Rur river discharge from 21.43 m³/s (average discharge) to 129.35 m³/s (flood discharge) reduces the arrival time from the Dutch border to Roermond to 12 hours, halving the arrival time. This significant difference is driven by the ’wet-bed’ effect. The Massive Flood wave reaches Roermond in 5 hours, attenuating to 3204 m³/s and causing flooding in Roermond. The resulting peak discharge in the Meuse river, just downstream of Roermond, reaches 2888 m³/s, remaining slightly below its design discharge of 3275 m³/s. The consequences for the Netherlands depend heavily on the peak discharge and volume of the flood wave hydrograph. The flooding caused by the Large Flood Wave would largely be confined to the Rur river floodplains, causing minimal urban flooding. However, direct economic damages is still estimated to approach 90 million euros, primarily due to rail and road infrastructure. Massive Flood wave flooding would have catastrophic consequences: floodwaters would extend far beyond the floodplains. The direct economic damage is estimated at 1.4 billion euros. These findings underscore the critical need for cross-border flood risk management. In particular, the implementation of an early-warning system, to ensure that residents can evacuate timely.
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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. ... Read more

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. ... Read more