The tidal bores occur in the shallow mouths of some rivers when high tides rise in the narrow funnel-shaped estuaries. There are two kinds of tidal bores. Low Froude numbers Fr lead to low turbulences in the river flows, inducing undular tidal bores. High Froude numbers Fr lead to high turbulences in the river flows, inducing breaking tidal bores. The study of sediment particle trajectories in tidal bores will help us to understand the mechanisms of sediment transport in the river flows where the tidal bore phenomenon can appear.

OPENFOAM, a CFD code, was used to simulate undular and breaking tidal bores by varying the Fr between 0.994 and 1.66. The validation of numerical simulations was performed by means of the Lemoine's theory. The analysis of the wave amplitude aw and the wave length Lw has allowed us to define the transition between the hydraulic jumps and the undular tidal bores, and the transition between the undular and breaking tidal bores. Lw approaches the infinity when the undular tidal bores become hydraulic jumps. The decrease of the wave amplitude aw is related to the presence of breaking tidal bores. The undular tidal bores appear for Fr > 1.21 and they become breaking for Fr > 1.38.

A tracker method, based on solving of Maxey-Riley equations, was used to estimate the trajectory of sediment particles in undular tidal bores. The analysis of sediment particle trajectories was performed by means of the Chen's model modified. The modication of the Chen's model uses three parameters denoted b1, b2 and b3. The relation between each parameter and the Froude number Fr was established. b1 related to the front celerity, decreases when Fr increases. The undular tidal bores move faster than the breaking tidal bores. b2 and b3, related to the elevation and the attenuation, increase when Fr increases. The train of undulations disappears with Fr. The turbulence is responsible of the disappearance of undulations.