Surface Turbulence on Bores and Surges propagating on Smooth and Rough Beds

Hydrodynamic waves are characterised by unsteady, highly turbulent and irregular behaviours. In nature, such phenomena can be observed in dam breaks, impulse waves and tsunamis. Both wet bed bores and dry bed surges were experimentally reproduced on smooth and rough surfaces. For all tested scenarios a front propagating in the channel was observed, with secondary waves with various frequencies occurring behind the propagating front. Such phenomena are probably a consequence of the non-hydrostatic pressure distribution around the bore front. The present study investigates in both time and frequency domains, the distribution of the frequencies observed on top of the bore. The latter represent the surface fluctuations of a bore behind the front. Measurements allowed to characterise the eddy-size distribution for all configurations. Results also showed that the most recurring frequencies are between 0.5 and 2 Hz. Furthermore, it was shown that the first part of the wave was characterised by high-amplitude oscillations associated with greater energy content.