Numerical modelling of three-dimensional wave-current interactions in complex environment: Application to Alderney Race

Modelling three-dimensional wave-current-turbulence interactions in extreme tidal environments is still challenging and necessary for the development of the tidal industry, particularly for the dimensioning of tidal converters. Following this objective, we focus our study on the most energetic tidal site in Western Europe, the Alderney Race (France). Due to the strong tidal current at this location, wave-current interactions were poorly studied by the past and often neglected. We propose to assess how they impact the Alderney Race hydrodynamic by the use of numerical modelling and in-situ measurements. In this study, the following wave-current interactions were observed: (i) Stokes drift effects inducing an increase/decrease in the current depending on the angle between waves and current, with a maximum influence near the surface, (ii) wave enhancement of the bottom friction reducing the tidal current, (iii) refraction of waves by the current, generating changes in waves directions, and (iv) wave breaking ascribed to tidal current, increasing the turbulent mixing. A non-stationary time delay, varying within a same tidal cycle, was noted, which is reduced by including the local wind effects and by adjusting the bottom stress formulation. This study shows that wave-current interactions play a non-negligible role in Alderney Race although the strong tidal current and that they need to consider by the tidal industry.