Storm-induced sediment supply to coastal dunes on sand flats

Abstract

Abstract. Growth of coastal dunes requires a marine supply of sediment. Processes that control the sediment transfer between the sub-tidal and the supra-tidal zone are not fully understood, especially in sand flats close to inlets. It is hypothesised that storm surge events induce sediment deposition on sand flats, providing fresh material for aeolian transport and dune growth. The objective of this study is to identify which processes cause deposition on the sand flat during storm surge conditions and discuss the relationship between the supra-tidal deposition and sediment supply to the dunes. We use the island of Texel as a case study, of 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 supra-tidal shore-parallel deposition of sand occurs in both the numerical model and the topographic data. The amount of sand deposition is directly proportional to surge level and can account for more than a quarter of the volume deposited at the dunes yearly. Furthermore, storm surges 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 reworking significant amounts of sand for aeolian transport in periods after the storm, and as such can also play a constructive role in coastal dune development.