Hydrodynamic Impacts of Tidal bores in Macro-Tidal Estuarine systems, laboratory experiments and numerical simulations. – MASCARET

The tidal bore is a fascinating, intense and powerful natural phenomenon. In macrotidal estuaries, a tidal bore occurs during spring tide conditions when the flood tide is confined to a narrow funnelled channel. The bore is a series of waves propagating upstream as the tidal flow turns to rising. Tidal bores can be observed in several places in France: Aquitaine, Baie du Mont-Saint-Michel, Brittany. However, a tidal bore is a very vulnerable process and results from a fragile balance between a number of parameters (e.g. bathymetry, tidal conditions, etc.). The tidal bore is a very important phenomenon for the estuarine eco-system (turbulence, great mixing capacity, sediment transport, remobilization of pollutants). Moreover, the tidal bores play a significant role on the ecology of an estuary. Tidal bore affected estuarine systems are known feeding and spawning grounds for various species. The disappearance of several bores was reported to adversely impact onto the ecosystem, with elimination of fish species. Tidal bores also impact human industrial activities. For example, some sections of the Airbus A380 travel on barges on the Dee and Garonne River estuaries that are both affected by tidal bores.
The existence of tidal bores is based upon an unstable hydrodynamic balance, which may be easily disturbed by changes in boundary conditions and freshwater inflow conditions. Man-made interventions led to the disappearance of several bores (harbour facilities, bridges, locks, dams, dredging operations, etc.). The famous mascaret of the Seine River no longer exists due to dikes constructions and dredging operations in its estuary. Even if the phenomenon has been reported for a very long time in numerous historic documents, the tidal bore phenomenon remains poorly understood, rarely studied in details. To date, we found only five field studies, some physical studies in laboratories and three numerical studies published in scientific literature.
Detailed investigations of the physical processes are needed to preserve this natural phenomenon. This multidisciplinary research project is innovative. However, because of the great complexity of the phenomenon, very few research teams are involved in tidal bores field studies and physical investigations. The partners involved in this project are internationally recognized as experts in their investigation domains. The majority of the works about tidal bores were published by researchers of the group. Three research teams with a range of complementary skills will use a range of innovative approaches. The success of this project relies in each team's ability to successfully employ state of the art tools and techniques, either experimental or numerical, and to make of use of these toward the understanding of the physics involved in the turbulent flow generated by the tidal bores. The partners are going to share their expertise for field surveys and their infrastructures (4 flumes of different sizes, different numerical tools for 3D simulations). The multidisciplinary team will work for a better understanding of the physical processes involved by this unique natural phenomenon and its impact on the environment, using different research approaches (field soil sampling, field surveys, laboratory studies, and numerical simulations). The induced sediment transport will be detailed (suspension, advection, scour), and the mixing capacity of suspended material (solid particles, biological elements) will be quantified. The bore‘s sensibility to some parameters modifications will be presented. The results will help for decision making, industrial and human activities (navigation on rivers, harbors developments, docks and bridges constructions, maintenance and consolidation of river banks, dredging operations, conservation of living species, pollution dispersion). Preserving this natural flow is a key consideration of this project.