Turbulence, sedimentary processes and tidal bore collision in the Arcins Channel, Garonne River (October 2013)

Reungoat, David, Chanson, Hubert and Keevil, Claire (2014) Turbulence, sedimentary processes and tidal bore collision in the Arcins Channel, Garonne River (October 2013). Hydraulic Model Report CH Series CH94/14, School of Civil Engineering, The University of Queensland.

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Author Reungoat, David
Chanson, Hubert
Keevil, Claire
Title Turbulence, sedimentary processes and tidal bore collision in the Arcins Channel, Garonne River (October 2013)
School, Department or Centre School of Civil Engineering
Institution The University of Queensland
Open Access Status Other
Report Number CH94/14
Series Hydraulic Model Report CH Series
Publication date 2014
Start page 1
End page 145
Total pages 147
Publisher School of Civil Engineering, The University of Queensland
Language eng
Formatted Abstract/Summary
A tidal bore is a series of waves propagating upstream in an estuarine zone, when the tidal flow turns to rising. It is an unsteady rapidly-varied free-surface flow generated by the rapid rise in water elevation during the early flood tide, when the tidal range exceeds 4.5 to 6 m and the channel bathymetry amplifies the flood tidal wave. Some unusual situations might be observed in natural systems, including tidal bore collision and crossing. This study describes a detailed field investigation in the Garonne River next to a bore crossing at Arcins (France). Some key features included a fine temporal resolution with 200 Hz velocity sampling rate, the complementary nature of the instrumentation (ADV, OBS, CTD), and a comprehensive characterisation of the sediment properties. The tidal bore was undular in the Arcins channel on 19 October 2013 and its Froude number was Fr1 = 1.27. The undular bore front was followed by some well-defined whelps. A most unusual feature was the collision between the Arcins channel tidal bore and the Garonne River main channel bore close to the southern end of the Arcins channel, about 800 m from the sampling site. The collision of the two tidal bores generated a transient standing wave with a dark black water mixing zone. Afterwards the Garonne River's main channel bore propagated 'backward' up to the northern end of the Arcins channel. It is suggested that the bore collision resulted from the siltation of the Arcins channel, delaying the propagation of the tidal bore in the silted channel and allowing the main channel bore to enter and develop at the southern end of the Arcins channel. The instantaneous 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, including during the 'backward' bore propagation. The amplitude of the instantaneous turbulent shear stresses was one to two orders of magnitude larger than the critical stresses for sediment motion onset. Large SSC estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters. The collision of tidal bores in the Arcins channel was a very unusual occurrence.
Keyword Undular tidal bore
Tidal bore collision
Garonne River
Turbulent mixing
Field measurements
Granulometry
Rheology
Suspended sediment concentration
Acoustic Doppler velocimetry
Salinity
Temperature
Additional Notes The report is open access. It was peer-reviewed by two independent expert. The full bibliographic details are: REUNGOAT, D., CHANSON, H., and KEEVIL, C. (2014). "Turbulence, Sedimentary Processes and Tidal Bore Collision in the Arcins Channel, Garonne River (October 2013)." Hydraulic Model Report No. CH94/14, School of Civil Engineering, The University of Queensland, Brisbane, Australia, 145 pages (ISBN 9781742721033).

Document type: Department Technical Report
Collection: School of Civil Engineering Publications
 
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Created: Mon, 26 May 2014, 08:45:12 EST by Hubert Chanson on behalf of School of Civil Engineering