Hydrodynamic Modelling of Wave Overtopping over a Block-Covered Flood Defence

Abstract

Wave overtopping can cause erosion on the landward slope due to high flow velocities and turbulence that cause high stresses on the cover. Innovative block revetments such as Grassblocks protect the subsoil of the dike against erosion. The blocks are permeable, which reduces the flow velocity and the pressures along the landward slope. The performance of these blocks is assessed in physical tests, which provides insights into the stability of the blocks. However, such experiments are expensive and accurate measurements are difficult due to highly turbulent conditions. Therefore, the goal of this study is to determine the hydrodynamic conditions at the dike cover caused by the wave run-up on the seaward slope and by the overtopping flow over the crest and landward slope. The geometry and wave conditions from the physical test at the Deltares Delta flume are implemented in an OpenFOAM® numerical model. Using the porousWaveFoam solver, a porous layer on the crest and landward slope is implemented, where the flow resistance of this porous layer largely depends on the resistance coefficients α [-] and β [-]. The numerical model is calibrated based on resistance coefficients as introduced earlier in the literature, which showed that the resistance coefficients of α=500 and β=2.0 performed best for the peak flow velocities and the peak pressures. The numerical model is evaluated by using these resistance coefficients in other time series of the physical tests. The evaluated model is then used to determine the hydrodynamic conditions on the landward slope, which showed that the pressure was the most influential hydrodynamic condition at the time of failure. Finally, the model showed that a porosity of n=0.6 and the porous layer thickness η=36 mm reduced the peak pressure the most.

The Effect Of Geometrical Transitions On The Wave Overtopping Load

“…New relations are developed for the hydraulic load of the overtopping flow at geometric transitions. These relations can be used in existing calculation methods for cover failure by overtopping waves to determine the cover erosion during storms Steendam et al, 2014) or asses the stability of covers (Barendse et al, 2022). For example, the relations can be used as a multiplication factor for the flow velocity in the GEM, WIM or COM.…”

“…These can not be measured during tests, but computational fluid dynamics CFD models can provide information on these variables. Several CFD models have been used to simulate the hydraulic load by waves on coastal structures with a hard revetment (Chen et al, 2021;Altomare et al, 2015) porous medium (Barendse et al, 2022;Palma et al, 2019) or grass cover (Van Bergeijk et al, 2020;Bomers et al, 2018). These models provide information on the spatially and temporal variation in the hydraulic variables and can be used to study the load on the cover by overtopping waves.…”

Over the dike top: modelling the hydraulic load of overtopping waves including transitions for dike cover erosion

“…This is not the case for the landward slope where the wave forces are smaller and the grass vegetation is able to resist large overtopping discharges (Section 1.2.1; Van Der Meer,2008). Interestingly, multiple strengthening techniques of the grass cover are proposed that can result in a different roughness once the grass cover is eroded, such as geogrid and Grassblocks (Van Steeg, 2016;Barendse et al, 2022). Additionally, the use of different types of vegetation covers have been investigated to increase the ecological value of flood defences (Scheres and Schüttrumpf, 2019) or to increase the resistance of the cover against droughts or extreme rainfall (Norton et al, 2016;Padilla et al, 2019).…”