The Role of Sea-Swell, Infragravity Waves, and Dune Geometry on Runup Excursion During Dune Collision

Abstract

Storm-elevated water levels can lead to waves attacking the dune face (dune collision regime), resulting in avalanching and shoreward translation of the dune face. Predicting dune erosion rates during storms is critical, yet, our knowledge of the relative role of infragravity and sea-swell waves on runup excursion on an eroding dune face relies primarily on numerical modeling. Here, we assess the role of sea-swell waves, infragravity waves, and dune geometry on runup excursion during dune collision with observations collected during the Realdune/REFLEX field experiment. In situ and lidar observations were collected from Oct. 2021 to Jan. 2022 at the Sand Engine in the Netherlands. Incident sea-swell and infragravity wave contributions resulting in runup on an artificial, unvegetated dune during two winter storms were quantified. We find that infragravity wave crests contributed to the largest runup events on the dune. Additionally, runup excursion is modified by dune geometry, where more sediment at the dune base, associated with a relatively mild dune face, reduced runup extent relative to events with steeper dune faces. This suggests that shallower dune geometries with more sand at the base may temporarily enhance dune safety by reducing runup.