In this paper, a Reynolds-averaged Navier–Stokes (RANS) equations solver, interFoam of OpenFOAM^®, is validated for wave interactions with a dike, including a promenade and vertical wall, on a shallow foreshore. Such a coastal defence system is comprised of both an impermeable dike and a beach in front of it, forming the shallow foreshore depth at the dike toe. This case necessitates the simulation of several processes simultaneously: wave propagation, wave breaking over the beach slope, and wave interactions with the sea dike, consisting of wave overtopping, bore interactions on the promenade, and bore impacts on the dike-mounted vertical wall at the end of the promenade (storm wall or building). The validation is done using rare large-scale experimental data. Model performance and pattern statistics are employed to quantify the ability of the numerical model to reproduce the experimental data. In the evaluation method, a repeated test is used to estimate the experimental uncertainty. The solver interFoam is shown to generally have a very good model performance rating. A detailed analysis of the complex processes preceding the impacts on the vertical wall proves that a correct reproduction of the horizontal impact force and pressures is highly dependent on the accuracy of reproducing the bore interactions.

Three open source wave models are applied in 2DV to reproduce a large-scale wave flume experiment of bichromatic wave transformations over a steep-sloped dike with a mildly-sloped and very shallow foreshore: (i) the Reynolds-averaged Navier–Stokes equations solver interFoam of OpenFOAM^® (OF), (ii) the weakly compressible smoothed particle hydrodynamics model DualSPHysics (DSPH) and (iii) the non-hydrostatic nonlinear shallow water equations model SWASH. An inter-model comparison is performed to determine the (standalone) applicability of the three models for this specific case, which requires the simulation of many processes simultaneously, including wave transformations over the foreshore and wave-structure interactions with the dike, promenade and vertical wall. A qualitative comparison is done based on the time series of the measured quantities along the wave flume, and snapshots of bore interactions on the promenade and impacts on the vertical wall. In addition, model performance and pattern statistics are employed to quantify the model differences. The results show that overall, OF provides the highest model skill, but has the highest computational cost. DSPH is shown to have a reduced model performance, but still comparable to OF and for a lower computational cost. Even though SWASH is a much more simplified model than both OF and DSPH, it is shown to provide very similar results: SWASH exhibits an equal capability to estimate the maximum quasi-static horizontal impact force with the highest computational efficiency, but does have an important model performance decrease compared to OF and DSPH for the force impulse.

Short duration bores in the coastal zone are generated by wave breaking in shallow water and mild foreshore conditions. In storm weather situations and for sea level rise scenarios, these bores approach the dike and interact with previously overtopped or reflected bores. Combined laser scanner and video measurements were used to study the complex and turbulent bore interaction processes. Five bore interaction patterns were distinguished as (1) regular bore pattern; (2) collision bore pattern; (3) plunging breaking bore pattern; (4) sequential overtopping bore pattern, and (5) catch-up bore pattern. Video images of the bore running up the wall and motion tracking of the leading edge were used to obtain a time series of the run-up water at the wall. The impact loads of the bore hitting the wall on the promenade were studied based on the signal of a vertical array of 13 pressure sensors installed over the wall height. Three impact types were distinguished and classified as (1) impulsive impact type; (2) dynamic impact type; and (3) quasi-static impact type. The majority of ~2/3 of the total number of impacts were comprised of the quasi-static impact type.

Currently a new wave flume for hydraulic experiments near to prototype scale is under construction at Deltares. In the flume, modern measurement equipment will be installed. One of the potential sensor techniques is Terrestrial Laser Scanner (TLS) based range measurements of water waves. TLS range measurements are a very fast and accurate method for solid surfaces, providing temporal and spatial high resolution profile measurements. The conditions under which measurements of water surfaces with TLS are possible are however less well understood. The main objective of this work is to explore possibilities to apply TLS based range measurements of water waves in the new Delta Flume facility. Hence, influencing parameters on TLS based range measurements from water waves in the laboratory are identified from literature. The influencing parameters are further investigated in a test featuring the SICK LMS 511 and measuring the water surface in the 50 m TU Delft wave flume. Analysis of the results provides an insight into the possibilities and potential problems of the new measurement method. The obtained profile measurements from a originally straight still water surface showed a tendency to bend upwards at the side of the profile. For that reason a surface correction method based on the refraction of the laser beam when entering the water is elaborated. This method is part of the derived wave field reconstruction method. Finally, an optimized water wave measurement set-up for the new Delta Flume proposed.

Large-scale physical experiments (Froude scale, 1:4.3) were performed at the new Delta Flume in 2017, aimed at investigating wave impacts on a vertical wall placed on the top of a dike in a mild slope shallow foreshore. Experiments also allowed to investigate the morphological evolution of the sandy foreshore, the scour at the dike toe and its development under irregular and bi-chromatic wave conditions. Both experimental results and numerical study performed to design the experiments are reported. Moreover, preliminary validation of the model to investigate the scour within a wider range of wave conditions and foreshore slopes is illustrated.

This study comprises a detailed description of the individual overtopped bore impact processes against a vertical wall, situated on top of a dike. A twin peak force impact signal shape was observed with two distinct peaks during every impact. The two peaks were assigned consecutively to the dynamic components (thickness and velocity) or hydrostatic components (run-up of water at the wall) of the impacting bore. The two peaks were termed dynamic F1 and quasi-static F2 impact respectively. Based on available literature semi-empirical equations to describe either the dynamic F1 or quasi-static F2 impact force were investigated and the prediction accuracy evaluated using impact force data from large-scale experiments. The prediction accuracy of the dynamic F1 impacts was very low. The prediction accuracy of the quasi-static impact F2 was increased based on fitting the hydrostatic theory to the maximum run-up measurement at the wall. Based on these findings 80% of the maximum run-up height was effectively contributing to the maximum quasi-static force F2 on the wall. The results coincided well with previous small-scale studies (Chen et al. 2012). After deconstructing the process chain preceding an impact, using the physically most meaningful parameters to predict the impact force, evaluating on a range of existing approaches, and observing the scattered prediction results, it was concluded that the impact behavior is highly stochastic and statistical analysis would be more beneficial.