Hydrodynamic and sedimentary processes of tidal bores: Arcins Channel, Garonne River in August-September-October 2015

Reungoat, David, Leng, Xinqian and Chanson, Hubert (2016) Hydrodynamic and sedimentary processes of tidal bores: Arcins Channel, Garonne River in August-September-October 2015. Hydraulic Model Report CH102/16, School of Civil Engineering, The University of Queensland.

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Author Reungoat, David
Leng, Xinqian
Chanson, Hubert
Title Hydrodynamic and sedimentary processes of tidal bores: Arcins Channel, Garonne River in August-September-October 2015
School, Department or Centre School of Civil Engineering
Institution The University of Queensland
Open Access Status File (Publisher version)
Report Number CH102/16
Series Hydraulic Model Report
Publication date 2016
Total pages 272
Language eng
Abstract/Summary A tidal bore is a compressive wave of tidal origin, propagating upstream as the tidal flow turns to rising. It might be observed when a macro-tidal flood flow enters a funnel shaped river mouth with shallow waters. The occurrence of tidal bores has a significant impact on the natural systems, the bore propagation being associated with intense sediment scouring and suspension of bed materials. The tidal bore of the Garonne River was extensively investigated in the Arcins channel in 2010, 2012 and 2013, typically over one to two days. Herein new field measurements were repeated systematically at the same site on 29 August-1 September 2015 and on 27 October 2015. The nature of the observations was comprehensive, encompassing hydrodynamics and turbulence, sedimentology and transport. The aim of the study was to comprehend the temporal evolution of hydrodynamics and sediment processes in the Garonne River estuarine zone during a spring tide period. Instantaneous velocity measurements were performed continuously at high-frequency (200 Hz) prior to, during and after each afternoon tidal bore. Instantaneous sediment concentration and suspended sediment flux data were derived from careful calibration of acoustic backscatter and checked against water sample concentration. Between 29 August and 1 September, the sediment material characteristics showed some temporal trend: (a) the bed material granulometry data showed a progressively broader grain size distribution associated with some increase in median sediment size; and (b) the apparent yield stress and effective viscosity of bed materials increased over the first four days of tidal bore occurrence. The tidal bore occurrence had a marked effect on the velocity and suspended sediment field, including a rapid flow deceleration and flow reversal during the bore passage. The turbulent Reynolds stress data indicated large shear stresses, together with large and rapid fluctuations, during the bore passage and the early flood tide. A turbulent event analysis was further conducted in the highly-unsteady rapidly varied tidal bore flow. The suspended sediment concentration (SSC) data indicated a gradual increase in initial mean SSC estimate prior to the bore from 29 August to 1 September 2015, and very large SSCs during the passage of the tidal bore front and early flood tide. A comparison between suspended sediment flux data showed very significant suspended sediment flux on 29 August 2015, i.e. on the first day of tidal bore occurrence, with a decreasing magnitude over the next three days. The data suggested a two-stage bed scour process: at each tidal bore event, surface erosion occurred initially, in the form of stripping; the first stage was followed by delayed mass erosion, occurring about 5-15 minutes after the tidal bore. The sediment flux data yielded a mass transport of about 500 tonnes of sediments per second in the 70 m wide channel, in average for the first hour of flood tide. The present work culminates a 5-year research project at the same site, showing a progressive siltation of the channel, particularly during the last three years.
Keyword Tidal bores
Hydrodynamics
Mud rheology
Granulometry
Suspened sediment concentration
Suspended sediment load
Turbulent flux events
Turbulence
Sedimentary processes
Institutional Status UQ
Additional Notes The report is open access. The full bibliographic details are: REUNGOAT, D., LENG, X., and CHANSON, H. (2016). "Hydrodynamic and Sedimentary Processes of Tidal Bores: Arcins Channel, Garonne River in August-September-October 2015." Hydraulic Model Report No. CH102/16, School of Civil Engineering, The University of Queensland, Brisbane, Australia, 270 pages (ISBN 978-1-74272-155-2).

Document type: Department Technical Report
Collection: School of Civil Engineering Publications
 
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Created: Wed, 03 Aug 2016, 14:29:28 EST by Hubert Chanson on behalf of School of Civil Engineering