# An experimental comparison of velocities underneath focussed breaking waves

## TL;DR

This study experimentally investigates how the shape of wave spectra influences the velocity fields of breaking waves, revealing deviations from standard engineering predictions under certain conditions.

## Contribution

It provides new experimental data on the impact of wave spectrum shape on breaking wave velocities, highlighting limitations of existing engineering models.

## Key findings

- Broader spectra produce energetic plungers at lower amplitudes.
- Narrower spectra break at higher amplitudes with less energetic spillers.
- Measured velocities can significantly deviate from engineering predictions.

## Abstract

Nonlinear wave interactions affect the evolution of steep wave groups, their breaking and the associated kinematic field. Laboratory experiments are performed to investigate the effect of the underlying focussing mechanism on the shape of the breaking wave and its velocity field. In this regard, it is found that the shape of the wave spectrum plays a substantial role. Broader underlying wave spectra leads to energetic plungers at a relatively low amplitude. For narrower spectra waves break at a higher amplitudes but with a less energetic spiller. Comparison with standard engineering methods commonly used to predict the velocity underneath extreme waves shows that, under certain conditions, the measured velocity profile strongly deviates from engineering predictions.