Storm-induced sediment supply to coastal dunes on sand flats

Abstract. Marine supply of sand can control the development and morphology of coastal dunes. However, processes that control the sediment transfer between sub-tidal and the supra-tidal zone are not fully understood, especially in coastal settings such as sand-flats close to inlets. It is hypothesised that storm surge events induce sediment deposition on sand-flats, so that this may influence dune development significantly. Therefore, the objective of this study is to identify which processes causes deposition on the sand-flat during storm-surge conditions and discuss the relation between the supra-tidal deposition and sediment supply to the dunes. We use the island of Texel as a case study, on which multi-annual topographic and hydrographic data sets are available. Additionally, we use the numerical model XBeach to simulate the most frequent storm surge events for the area. Results show that a supra-tidal shore-parallel deposition of sand occurs in both the numerical model and the data. The amount of sand deposition is directly proportional to surge level, and can account for more than half of the volume deposited at the dunes on a yearly basis. Furthermore, storms are also capable of remobilising the top layer of sediment of the sand-flat, making fresh sediment available for aeolian transport. Therefore, in a sand-flat setting, storm surges have the potential of adding significant amounts of sand for aeolian transport in periods after the storm, suggesting that storms play a significant role in the onshore sand supply between sub-tidal and subaerial zones in those areas.