Tidal Bore and Bathymetry (Augmented) – BABA

A tidal bore is the tidal wave front forming in macrotidal estuaries, and traveling up in the river. Depending on tidal ranges, fluvial discharge and channel morphologies, the tidal bore development differ when the tidal wave front meets the river flow. Estuaries are morphological systems adapting to base level variations, tidal cycles, river discharge, sediment supply and human modifications. The factors of tidal bore formation and dynamics are identified. They are not yet understood due to their variability and not discriminant enough. BABA aims in studying the interaction between bathymetry and tidal bores with 4 approaches. WP1 History using a technique of optical processing of nautical charts. Old water depth data along the Dordogne river will be introduced into hydro-morphodynamic models in order to study how bathymetric changes affect tidal bore development on the long-term. WP2 In situ measurements in the inner estuaries of Sée and Dordogne rivers. Measurements will assess at small scales of time and space the impact of bathymetry on the generation and propagation of tidal bores, and their impact on the channel morphology during successive tides. WP3 Laboratory experiments in open channels. Tidal bores will be generated with variable beds, fixed or mobile. A tidal bore generation mechanism similar to that observed in nature with an ebb reversal followed by a short flood, will be tested. The data will assess the tidal bore hydrodynamics and their role on sediment reworking. Rheological properties of sediments of Sée and Dordogne rivers will be characterised and used in an open channel. WP4 Modeling and numerical simulations. The tools to simulate the free surface deformation before and during breaking, and the generation of vertical structures will be evaluted. From the hydrodynamic predictions understood, the data of WPs will be used to generate the meshes and to calibrate the bedload transport rate and the turbulence models used in numerical simulations.