Abstract
This paper presents numerical modelling of the nearshore transformation of infragravity waves induced by bichromatic wave groups over a horizontal and a sloping bottom. The non-hydrostatic model SWASH is assessed by comparing model predictions with analytical solutions over a horizontal bottom and with detailed laboratory observations for a sloping bottom. Good agreement between model predictions and data is found throughout the domain for bound infragravity waves. Furthermore the model predicts greater outgoing free infragravity wave-heights for steeper slope regimes which is consistent with the measurements. The model however tends to overestimate the magnitude of the outgoing infragravity waves.
Highlights
Infragravity waves are surface gravity waves with periods ranging from 20s to 250s which are generated by the group structure of the short waves
A significant decay in the wave height is observed for x>25m and this is chosen as the transition between the shoaling region and the surf zone
In this study we demonstrated the capabilities of SWASH, a non-hydrostatic phase-resolving wave model, in simulating the transformation of infragravity waves induced by a bichromatic wave-group propagating over a horizontal bottom and over a plane slope
Summary
Infragravity (ig) waves are surface gravity waves with periods ranging from 20s to 250s which are generated by the group structure of the short waves. Roelvink et al, 2009), which makes ig-waves an important subject for coastal engineers. Several types of numerical models are available to study ig-waves. ‘Surf-beat models’ simulate igwaves by combining a wave driver model, which provides the forcing of the wave groups, with a shallow water model that accounts for the near-shore transformation of the ig-waves Ig-waves can be modelled by phase-resolving models based on a Boussinesqtype formulation Stelling and Zijlema, 2003) These phase-resolving models account for all relevant near-shore processes (e.g. shoaling, refraction, reflection, and non-linearity) and thereby provide a potentially more accurate, but computationally more expensive approach
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