High frequency variability of particle size distribution and its dependency on turbulence over the sea bottom during re-suspension processes

• Estimation of the particle size distribution slope at high frequency.
• Similar power spectra of PSD slope and turbulent velocity are found.
• Mean particle diameter dynamics is similar to velocity׳s.
• Two power-law regimes are found for particle parameters and velocity.
• The role of turbulence on particle׳s re-suspension dynamics is studied.

The impact of tidal current, waves and turbulence on particles re-suspension over the sea bottom is studied through Eulerian high frequency measurements of velocity and particle size distribution (PSD) during 5 tidal cycles (65 h) in a coastal environment of the eastern English Channel. High frequency variability of PSD is observed along with the velocity fluctuations. Power spectral analysis shows that turbulent velocity and PSD   parameters have similarities in their spectral behaviour over the whole range of examined temporal scales. The low frequency variability of particles is controlled by turbulence (β≃−5/3)(β≃−5/3) and the high frequency is partly driven by dynamical processes impacted by the sea bottom interactions with turbulence (wall turbulence). Stokes number (St), rarely measured in situ, exhibits very low values, emphasizing that these particles can be considered as passive tracers. The effect of tide and waves on turbidity and PSD is highlighted. During slack tide, when the current reaches its minimum value, we observe a higher proportion of small particles compared to larger ones. To a lower extent, high significant wave heights are also associated with a greater concentration of suspended sediments and the presence of larger particles (larger Sauter׳s diameter DA, and lower PSD slope ξ).