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ABSTRACT
A tidal bore is an unsteady rapidly-varied open channel flow generated by the swift advance of the early flood tide in a funnel-shaped river estuary when the tidal range exceeds 4.5 to 6 m. This contribution presents a detailed field investigation conducted on the tidal bore of the Garonne River (France). The bore was undular and the bore's leading edge was followed by well-defined secondary waves, or whelps. The instantaneous ADV velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage. The investigation characterized some unusual transient turbulence caused by the bore propagation in a large river system, and the results suggested the advection of large-scale eddies in the wake of the bore front. The present study highlighted the need for detailed field measurements with fine temporal resolution, to characterize the highly unsteady rapidly-varied nature of tidal bore flows.
Acknowledgements
The authors acknowledge the assistance of Patrice Bengiati and the permission to access and use the pontoon in the Bras d'Arcins. They thank all the people who participated to the field work, without whom the study could not have been conducted. They further thank a number of scholars for their input and advice, in particular Professor Dan Parsons (University of Hull, UK), Dr Frédérique Larrarte (IFSTTAR Nantes, France), Professor Michael Bestehorn (Brandenburg University of Technology, Germany) and Professor Pierre Lubin (University of Bordeaux, France). The authors acknowledge the financial assistance of the Agence Nationale de la Recherche (Projet MASCARET 10-BLAN-0911-01).
Notation
| A | = | cross-section area (m2) |
| A1 | = | inflow cross-section area (m2) |
| A2 | = | conjugate cross-section area (m2) |
| aw | = | wave amplitude (m) |
| B | = | channel width (m) |
| B′ | = | characteristic channel width (m) |
| B1 | = | inflow free-surface width (m) |
| d | = | water depth (m) |
| d1 | = | inflow depth (m) |
| d2 | = | conjugate flow depth (m) |
| = | Froude number (–) | |
| g | = | gravity acceleration (m s−2) |
| H | = | hole size (m2 s−2) |
| Lw | = | wave length (m) |
| TVx | = | integral time scale of longitudinal velocity component (s) |
| TVy | = | integral time scale of transverse velocity component (s) |
| TVz | = | integral time scale of vertical velocity component (s) |
| Tw | = | wave period (s) |
| t | = | time (s) |
| U | = | bore celerity (m s−1) positive upstream |
| Vx | = | longitudinal velocity component (m s−1) |
| Vy | = | tranverse velocity component (m s−1) |
| Vz | = | vertical velocity component (m s−1) |
| V1 | = | inflow velocity (m s−1) |
| v | = | velocity fluctuation (m s−1) |
| vx | = | longitudinal velocity fluctuation (m s−1) |
| vy | = | transverse velocity fluctuation (m s−1) |
| vz | = | vertical velocity fluctuation (m s−1) |
| vx′ | = | longitudinal velocity fluctuation root mean square (m s−1) |
| vy′ | = | transverse velocity fluctuation root mean square (m s−1) |
| vz′ | = | vertical velocity fluctuation root mean square (m s−1) |
| x | = | longitudinal coordinate positive downstream (m) |
| y | = | transverse coordinate positive towards Arcins Island (m) |
| z | = | vertical coordinate positive upstream (m) |
| ρ | = | water density (m3 s−1) |