Wave Overtopping and Overwash of Dunes

Wave-induced overwash of sand dunes may cause rapid profile changes and possible dune destruction, thus increasing the flood risk landward of dunes. Accurate modeling of the wave overwash processes is therefore essential in predicting dune profile evolution during overwash events. However, available field and laboratory data are very limited. We measured dune profile evolution and overwash transport rates for three tests with different initial dune geometries in front of a low-crested vertical wall exposed to the same wave conditions in a wave flume. In all three tests, the transition from minor to major overwash occurred rapidly but the resilience of the dune against destruction depended on its initial geometry. During minor overwash, offshore sediment transport caused most of the dune crest lowering. These tests are used to assess a numerical model for wave overtopping and overwash of a dune. The numerical model is shown to be in agreement with the measurements of the free surface elevations, fluid velocities, and dune profiles. However, beach erosion in front of the exposed wall is underpredicted.