Bassin study of vetically sheared currents from the dispersion of surface gravity wave

Wave conditions from the open sea to the coast, provide necessary information, the good understanding and modeling of coastal dynamics, the design of coastal engineering structures coastal engineering structures, for navigation or the flooding risks evaluation. It is also a potential way to access information present below the surface. Refraction, diffraction and reflection of waves are not only forced by variations in bathymetry but also by the presence of currents. However, the effects of current in propagation models have long been limited to the consideration of homogeneous current in the water column. Nevertheless, currents are usually observed to be sheared vertically by wind, tides or waves. When wave propagate in the presence of currents their celerity is modified. It is also affected by the vertical structure of the current.

This work proposes and discusses methods for reconstructing current fields from wave data based on synchronous analysis of wave spectra at different points in space. We consider here the 2D case of progressive or partially stationary waves in the presence of homogeneous currents or with a vertical sheared profile. The study is based on data from experiments carried out at the Bassin de Génie Océanique FIRST(BGO), for progressive or partially stationary waves in the framework of the ANR project MORHOC'H 2. These test campaigns allowed us to test the sensitivity of the wave’s phase evolution during its propagation in order to estimate the feasibility of reconstructing either constant or sheared currents in the water column. Under the assumption of a progressive wave, the study of the phase evolution shows a significant influence of the current, allowing to reach the intensity of a uniform current. The calculated phase evolution in the presence of sheared current is consistent with the theory, but for small values of shear, the phase velocity changes are much smaller, making the method more sensitive to "noise". Furthermore, for a partially stationary wave, a significant impact of its phase evolution is observed in the propagation direction of the incident wave even for weak reflections, making it necessary to include this parameter in the reconstruction of currents from synchronous wave measurement data.

Acknowledgements:

The DGA is thanked for funding the AID thesis grant of Alexandra CUEVAS, as well as for the ANR grant: ANR-21-ASM1-003.