Turbulence measurements in the Garonne river tidal bore: first observations

A tidal bore is an abrupt rise in water depth advancing in some estuaries during spring tide conditions. In the present study, some detailed turbulence field measurements were conducted continuously at high-frequency (64 Hz) in the Garonne River tidal bore. The turbulent velocity components were sampled with an acoustic Doppler velocimeter (ADV) at 0.8 m beneath the freesurface. On 10 and 11 Sept. 2010, the tidal bore was undular as it passed in front of the sampling site. The tidal bore Froude number estimated from the channel bathymetry and observations was equal to 1.20 and 1.30 on 10 and 11 Sept. 2010 respectively. The turbulent velocity data showed the marked impact of the tidal bore propagation. The longitudinal velocity component highlighted some rapid flow deceleration during the passage of the tidal bore, associated with a sudden rise in the free surface elevation, and a flow reversal after the tidal bore front passage. The Reynolds stress data indicated some large amplitudes and rapid fluctuations during the tidal bore and flood flow. These field observations are the first detailed turbulence measurements in a tidal bore with high spatial and temporal resolutions.