Computational modelling of coastal flooding caused by combined surge overflow and wave overtopping on embankments

In this paper, we investigate the process of embankment wave overtopping combined with overflow because of extreme surge levels that are above the embankment crest. A Reynolds-averaged Navier-Stokes volume of fluid (RANS-VOF) model is employed to simulate the hydrodynamics. To investigate the success of the model at reproducing the hydrodynamic processes, the model is compared with experimental laboratory measurements. Comparisons are performed for quantities including discharge, depth and velocity. The overtopping discharge predicted by the model is compared against empirical design methods. Specific conditions under which discrepancies occur between the model, laboratory measurements and design formulae are identified and explained and design guidance is provided. This study has demonstrated that the RANS model can adequately represent the complex hydrodynamics encountered in extreme storms where combined overflow and wave overtopping occurs. A tendency was found for the model to somewhat over-predict the overtopping volume as wave heights increase and has been hypothesised as being due to shortcomings of the representation of turbulence within the model.