The importance of infragravity waves in the cross-shore sediment transport in the surf zone of a barred intertidal beach

Abstract

Knowledge about the sediment transport processes active in the intertidal zone is incomplete. Especially the role of infragravity waves, waves with a period of 20-200 seconds, remains unclear. Many authors propose mechanisms by which infragravity waves cause suspended sediment transport in the surf zone. Most mechanisms are based on only small data sets and the resulting suspended sediment transport varies in directions and magnitude. A field campaign of five weeks at the beach of Egmond aan Zee, The Netherlands, was performed to analyse the suspended sediment transport by infragravity waves in the surf zone. 384 bursts of 30 minutes were selected for analysis. The Importance of infragravity waves was strongly related to the normalized location within the surf zone strongly. The normalized location within surf zone was also used to explain the suspended sediment transport by infragravity waves. The infragravity wave suspended sediment transport was comparable in magnitude with the landward directed gravity wave suspended sediment transport. In most of the surf zone seaward directed mean suspended sediment transport component was dominant. It is proved that multiple infragravity wave suspended sediment transport mechanisms were active in the surf zone. A unifying theory of infragravity suspended sediment transport as a function normalized location within surf zone is proposed.