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

(IF 2.98; Q1); International audience; 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 Alderney Race (France) where the strongest tidal current in Western Europe and various sea states occur. Due to the strong tidal current at this location, wave-current interactions were poorly studied by the past. Therefore, we propose to assess the impacts of wave-current interactions in Alderney Race by the use of a 3D fully-coupled wave-current numerical model and in-situ measurements. The following wave-current interactions were observed : i) Stokes drift e ects inducing an increase/decrease in the current depending on the angle between waves and current, 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. The impact of such interactions were maximal near the reverse event ( 1h30) and for a weak/medium tidal range. A non-stationary time delay, varying within a same tidal cycle, was noted at both locations, which is reduced by including the local wind e ects and by adjusting the bottom stress formulation. This study shows that wave-current interactions play a non-negligible role in Alderney Race and that they need to consider by the tidal industry.