Accounting For Directional Wave Spreading Effects On Infragravity Wave Growth In A 1D Dune Erosion Model

Abstract

For reasons of computational efficiency, 1D XBeach cross-shore transect models are often applied on quasi alongshore-uniform coasts instead of a more computationally expensive 2DH modelling approach. In this paper we describe a practical methodology to allow 1D models to mimic infragravity wave growth observed in field conditions and represented in 2DH models and thereby significantly reduce the overestimation of infragravity wave heights near to the shore. We show that even if the coastal setting may support the 1D model assumption of alongshore uniformity in forcing and bathymetry, 1D XBeach models will overestimate infragravity wave growth relative to field conditions due to the underlying assumption of alongshore-uniform intra-wave (group) hydrodynamics common to all wave (group)-resolving models. Model analysis showed little variation in the optimum calibration value of this approach for a large range of wave forcing conditions (wave height, period and directional spread) and consistency with 2DH model results for a large range of Dutch coastal profiles. Comparison to field observations showed that the methodology significantly increased the skill of the 1D model to simulate nearshore IG wave heights. These results have implications on the ability to accurately predict the response of these coasts to energetic events, which is crucial to assess current and future flood risk and to design effective flood protection and mitigation measures.