Assessing dune erosion: 1D or 2DH? The Noorderstrand case study

The Dutch safety assessment rules primarily focus on the cross-shore processes related to dune erosion during an extreme storm. A case study of the Noorderstrand (Schouwen) reminds us of thee importance of taking into account effects of these alongshore processes. Both a study of the available (GIS) data and an extensive study with the numerical mmodel XBeach show various processes that influence the amount of dune erosion during an extreme storm. Long-term processes that lead to migration of sand waves on the beach as well as the edge of the nearby channel building out seaward are present in both the measurement data and the model simulations. The resulting variation in the beach geometry causes a strong redistribution of sediment in alongshore direction during an extreme storm, leading to a sediment balance difference up to 100 m3/m measured along a cross-shore transect. Redistribution of the sediment alongshore proves not only to be dependent on the beach geometry, but also on the wind direction during the storm.