Sensitivity of dune erosion predictions to wave obliquity

Coastal dunes protect large parts of the Dutch coast against flooding. These flood defences are regularly assessed for their safety against flooding. For this purpose, flood defence managers can make use of an assessment methodology based on the XBeach model in 1D mode, in which waves are assumed to be normally incident to the coast (i.e., approaching perpendicular to the shore). The effect of this assumption on computed dune erosion, and its implications for the flood risk assessment, have not previously been investigated. Continued development of dune safety assessment instruments, such as XBeach in 2DH mode, therefore requires an understanding of the sensitivity of simulated dune erosion to the angle of wave incidence.

The primary objective of this research is to quantify the sensitivity of dune erosion simulated in XBeach in 2DH mode to the angle of wave incidence, in the context of flood risk analysis. The secondary objective is to estimate the uncertainty surrounding the observed model sensitivity. To do so, sensitivity studies were performed for three different schematic test cases: 1) a straight, uniform dune coast (elementary dune flood defence), 2) a dike-to-dune transition, and 3) a curved dune coast (complex dune flood defence). Sensitivity simulations for a selection of JarKus profiles were included to account for variations in shoreface bathymetry and location along the Dutch coast.