CROSS-SHORE STRUCTURE OF INFRAGRAVITY STANDING-WAVE MOTION AND MORPHOLOGICAL ADJUSTMENT - AN EXAMPLE FROM NORTHERN ZEALAND, DENMARK

A set of eight manometer tubes was deployed across a barred surf zone in Northern Zealand, Denmark in order to resolve the cross-shore struc ture of infragravity wave motions. During a storm, a single dominant s tanding infragravity wave was generated. This wave had a frequency sim ilar to waves observed on previous occasions. Nearshore bars migrated 5-10 m landward (bar 1) and seaward (bar 2), respectively, with maximu m accretion occurring close to the antinodes of the standing wave. The field data thus support theoretical models for bar formation and adju stment, according to which bars are generated through suspended sedime nt transport convergence at infragravity standing wave antinodes. The generation of the infragravity waves was investigated using bispectral analysis techniques. It was found that during the peak of the storm, two separate incident wave components transferred energy to the infrag ravity wave. As the storm waned, the incident wave components became f urther separated in frequency space. Simultaneously, the standing infr agravity wave decayed.