Dispersion of Fish Eggs under Undular and Breaking Tidal Bores

A tidal bore is a wall of water propagating upstream as the tidal flow turns to rising into an estuary with a tidal range larger than 5 to 6 m and the bathymetry that amplifies the tidal wave. The bore front is a shock characterised by a singularity of the free-surface and pressure and velocity fields. This study aims to characterise the impact of tidal bores on the turbulent dispersion of fish eggs. Some physical modelling was performed based upon a Froude similitude and the tracking of plastic beads acting as fish egg proxies was conducted under controlled flow conditions with both undular and breaking tidal bores. The physical experiments highlighted some large-scale coherent structures generated beneath the bore front and advected behind. The vortical structures were responsible for some selective longitudinal dispersion of fish eggs depending upon the eggs’ relative density.