Wind-wave induced oscillatory velocities predicted by Boussinesq models
J. Bosboom (WL Delft Hydraulics, TU Delft - Coastal Engineering)
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Abstract
Sediment transport predictions are critically dependent on the prediction of near-bed wave-induced velocities. Especially the asymmetry between the forward (onshore) and backward (offshore) velocities plays an important role in determining the magnitude and direction of the wave-induced sediment transport.
Boussinesq wave models are amongst the most advanced wave models presently available to the coastal engineer. Moreover, they are highly efficient from a computational point of view. They are generally applied for wave propagation studies in which the focus is on the prediction of surface elevations. The knowledge about the capability of these models to predict the horizontal velocities under waves is limited.
This work aims to explore the possibilities of using such a Boussinesq model for the prediction of the nearbed velocities. A spectral Boussinesq model is used in which wave breaking and dissipation in the surf zone are included. The model is tested against measurements of irregular (partially) breaking waves performed in WL | Delft Hydraulics’ Delta flume.
The comparison of measured and computed velocity asymmetry indicates that for moderately long waves the Boussinesq model can be succesfully used for sediment transport purposes. For shorter waves the crest velocity values of the higher waves are underestimated and as a result the velocity asymmetry as well.
The work was started as part of the MAST-2 G8 Coastal Morphodynamics Research Programme and finalised as part of the MAST-3 SAFE project. It was funded jointly by the Commission of the European Communities, Directorate General for Science, Research and Development under contract no. MAS2- CT92-0027 and MAS3-CT95-0004, and Delft Hydraulics and Delft University of Technology in the framework of the Netherlands Centre of Coastal Research (NCK). The laboratory data used was obtained during experiments in the framework of the “Access to Large-scale Facilities and Installations Programme” (LIP), which were funded by the Commission of the European Communities, Directorate General for Science, Research and Development under contract no. GE1*- CT91-0032 (HSMU).
This paper is based on work first published in Coastal Engineering 23 (1997). Figures 8, 9 and 10 are used courtesy of Elsevier Scientific Publishers. The author wishes to thank J.A. Battjes, G. Klopman and J.A. Roelvink, Netherlands Centre for Coastal Research (NCK), for their many suggestions during the performance of this study.