A Numerical Modeling Approach to Capture Erosion around Coastal Protection Structures under Wave Impact

Common structure to protect the coastline against wave impact and erosion are seawalls. Whereas seawalls are effective at preventing coastal erosion during storm events, the wave energy is not dissipated. Waves are propagation on a sloping beach towards the seawall, where they interact with the vertical structure. Resulting from the incident and reflected waves, downward directed vertical velocity components cause a region of increased bed shear stress at the toe of the seawall, ultimately leading to local scour. Future climate change induced sea level rise and increased wave heights create a need for estimating possibly larger scour holes around seawalls which can threaten their structural stability. In this contribution, a solution strategy for the prediction of seawall scour scenarios for different water levels and wave conditions is presented. The high-resolution NavierStokes solver of the open-source hydrodynamics framework REEF3D is used to calculate the waves impacting the seawall. The interface capturing level set method for the free surface makes it possible to resolve the complex wave pattern in front of the seawall including the breaking of individual waves. Based on the near-bed flow conditions, the bed shear stress is calculated. Then bed load and suspended sediment transport formulations are numerically solved. Erosion and deposition of the sediment is calculated with Exner’s equation for the conservation of sediment mass. The morpho-hydrodynamic solver requires relatively large computational resources and is suitable for the near-field solutions. In order to predict realistic wave conditions at a given coastline location, more efficient large-scale wave models are required. A coupling strategy for a fully nonlinear potential flow model to the Navier-Stokes solver is presented. The numerical modeling results are validated against measured wave and sediment data from laboratory experiments.