Strong currents and waves during storm surges often cause coastal erosion and sediment transport, which may significantly damage the coastal ecosystem [1]. This study presents a fully coupled hydrodynamic and sediment transport model to predict beach erosion and morphological changes caused by storm-induced overwash. In the model, the shallow water flow model is coupled with Simulating Waves Nearshore (SWAN) model through wave radiation stress. The non-equilibrium sediment transport equation is used for the total-load sediment by considering wave and current interaction, as well as bed changes. The governing equations of the model are solved by employing the explicit finite-volume approach based on a rectangular mesh. The Godunov-type central upwind scheme is adopted to calculate the interface fluxes, thereby solving the complex Riemann problem. The established model is applied to simulate the erosion process on the Santa Rosa barrier island caused by the storm surge during Hurricane Ivan [2]. The results indicate that the model accurately predicts the real-case erosion process caused by storm surge and overwash. As shown in Figure 1, the simulated results clearly show that several breaches located in the area with low topography occurred when storm surge run over the top of the sandy barrier as indicated by the red dotted boxes (Zone 1, 2, and 3).

In marine engineering, the stability of sizeable vertical pile foundations is crucial for the safety of marine structures. Designing safe offshore structures entails addressing a series of dynamic seafloor responses caused by waves scouring pile foundations. Regarding numerical simulation, recent research has focused on building wave-structure-seabed interaction (WSSI) models. The WSSI model is developed based on OpenFOAM software, which consists of a wave model (Wave2Foam) and Biot's poroelastic model [1]. Previous work only considered the impact of wave scouring on the cylinder but ignored the role of currents [1, 2]. Therefore, future work will develop further on the WSSI model and construct a wave-current-structure-seabed interaction (WCSSI) model to study the migration in the riverbed caused by the simultaneous action of waves and currents. Furthermore, the model will be used to explore the seabed response around single-pile foundations and multi-pile foundations.

The BenO Wadden Sea research programme contributes to Rijkswaterstaat’s management practices by having become a central point in the organization (and beyond) where knowledge is available on the complex sediment dynamics of the Dutch Wadden Sea, providing evidence-based advice for navigability and nature conservation, while also thinking ahead. We experience that it needs time and commitment to consolidate the knowledge foundation, connect to colleagues and gradually develop and improve our management practices. We will highlight several of the studies that we have done over the last years, and their implications for management & maintenance.

The status of the Scheldt estuary is assessed periodically using the so-called Evaluation Methodology Scheldt Estuary. Recently, sediment transport capacity was included as a new explaining parameter for the status of the estuarine morphology, especially regarding the stability of the multi-channel system in the Western Scheldt. Sediment transport capacity can be defined as the capacity of the tidal flow to mobilize or transport sediments, as if the sediment is always present. This could apply to locally available sediments or to sediments that are disposed in dredging operations. A structured methodology is developed to compute and assess this sediment transport capacity based on numerical model simulations. Both the gross and net sediment transport capacity are assessed using the Scaldis model in TELEMAC-3D. Here, the net transport capacity distinguishes between a transport capacity during the flood and ebb periods, whereas the gross transport capacity represents the total transport over a tidal cycle. The model output consists of spatial covering maps of the gross- and net sediment transport capacity, based on a single representative tide. In addition, the gross- and net sediment transport capacity are also computed through a series of transects throughout the estuary, now based on a full spring-neap cycle. The developed methodology is applied to simulations with the 2011, 2013, 2016 and 2019 bathymetry as well as to historical Scaldis models of 1930, 1960, 1980 and 2020, in which several embanked tidal branches where still connected to the estuary and recent channel enlargements did not yet take place. A comparison between the computed transport capacities for different years can be used to analyze the trends or often subtle changes as a result of the natural morphological development, historical embankments, channel enlargement or the applied disposal strategy. The transport capacity is also used to support the permit applications for the disposal strategy in the Western Scheldt. Ultimately, these assessments could aid an optimized sediment management strategy.

We can define local scour as the removal of bed sediment at the vicinity of a structure induced by local accelerations of the near-bed velocity as well as the turbulence associated with the flow-structure interaction. Local scour is commonly classified in two distinct regimes: live-bed scour and clear-water scour. In live-bed scour sediment motion occurs independently of the presence of an obstacle, whereas in clear-water scour the sediment motion occurs exclusively near and downstream of an object.   The prediction of local scour is of particular interest for the design of hydraulic structures such as bridge or dock piers, hydraulic turbines, or wind farms alongside a coast. However, natural phenomena such as tidal currents or storm surges can complicate this prediction. For instance, while floods may lead to live-bed scour at the base of the central piers of bridges, those located at the floodplain can experience clear-water scour. This study presents a numerical investigation of the scour process at the base of square-shaped piers in two different orientations and under different flow confinement conditions to study the effects of the pier geometry and the wall proximity in both clear-water and live-bed conditions. Notably, the results indicate that the geometry of the pier has separate effects in both scour regimes.   The simulations were performed using an in-house research code that employs a second-order unstructured finite-volume approach to solve the three-dimensional Navier-Stokes equations in sigma-coordinates. The turbulence is modeled using a Large-Eddy-Simulation method. The bed evolution is modeled by the Exner-Polya equation. The research code has been used successfully to study local scour under live-bed conditions and clear-water conditions, and is currently applied for a broader study to investigate the effect of different variables.