Three-Phase Flow at the Geophysical Scale: the Tidal Bore

Tidal bores form in the river mouth when the tide turns to rising in a funnel-shaped estuary under spring tide conditions (tidal range greater than 5 to 6 m). A tidal bore is a hydrodynamic shock characterised by a discontinuity in terms of the free-surface elevation, and the velocity and pressure fields. Tidal bores have a massive impact on the estuarine zone: a tidal bore is a ‘giant mixer’ that stirs bed material and advects upstream sediment materials; and air is entrained in the bore roller and contributes to some re-oxygenation. Ecological impact in terms of fish reproduction, spawning and fish egg dispersion in tidal bore affected estuaries were documented: Rokan River (Indonesia), Bay of Fundy (Canada).