Sediment inception under breaking tidal bores

Khezri, Nazanin; Chanson, Hubert

doi:10.1016/j.mechrescom.2012.02.010

Cited by 14 publications

(16 citation statements)

References 4 publications

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“…Bores observed in this study had Froude numbers ranging from 1Á11 to 1Á47, corresponding with the undular (F r < 1Á3) and breaking, turbulent (F r > 1Á4) bores observed by Khezri & Chanson (2012a,b); whereby turbulent breaking bores have been documented to set particles in motion (Khezri & Chanson, 2012b). The bores during the 13 to 14 October 2012 flood appeared most turbulent and more frequently during rising and peak flow stages, and it is thought that these bores exerted more energy to remobilize parts of the bed surface.…”

Section: Lens Preservationsupporting

confidence: 66%

Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat, West Indies

2017

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The wavelength of stationary water-surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand-bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of the lenses was empirically related to antidune wavelength, and thus could be used to estimate flow velocity and depth. This study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting, testing the previously published relationship at a field-scale. Trains of stationary and upstream migrating water-surface waves were prevalent during the flash flood in October 2012 in the Belham Valley, Montserrat, West Indies. Wave positions and wavelengths were assessed at 900 sec intervals through the daylight hours of the event within a monitored reach. The wave data indicate flow depths up to 1Á3 m and velocity up to 3Á6 m sec À1 . Sedimentary structures formed by antidune growth and change were preserved in the event deposit. These structures include lenses of clast-supported gravel and massive sand, with varying internal architecture. The lenses and associated low-angle strata are comparable to sand-bed structures formed from stationary and upstream migrating waves in flume experiments, confirming the diagnostic value of these structures. Using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow.

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Section: Lens Preservationsupporting

confidence: 66%

Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat, West Indies

2017

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“…A reasonably good agreement was found between the experimental observations and theoretical equation, although the latter was developed ignoring bed friction. A similar finding was reported by Chanson (2010b), Docherty and Chanson (2012) and Khezri and Chanson (2012b). Considering an undular bore, the undulations have a quasi-periodic shape (Chanson, 2010a).…”

Section: Iv332 Free Surface Properties Based Upon Froude Number Cosupporting

confidence: 87%

“…A similar method was used by Koch and Chanson (2005), Docherty and Chanson (2010) and Khezri and Chanson (2012b). After rapid closure, the water initially accumulated against the gate, thus increasing the water depth and creating a surge propagating upstream into the channel.…”

Section: Iii324 Unsteady Flow Generationmentioning

confidence: 98%

“…A constant head tank supplied the water into a large basin leading to the channel through a bed and sidewall convergent. The same channel with a similar set up was used previously by Docherty and Chanson (2012) and Khezri and Chanson (2012b). The tainter gate used to generate the unsteady flow was located next to the downstream channel end at x = 0 when fully-closed and vertical as sketched in Figure III.2a.…”

Section: Iii3 Experimental Study Iii31 Facilitymentioning

confidence: 99%

“…The overall thickness of the gravel bed (plywood sheet and glued gravels) was on average 15 mm and it was installed between x = 0.59 m and x = 9.15 m from the gate. The fixed gravel bed configuration was selected to continue experiments with the same set up as Docherty and Chanson (2012) and Khezri and Chanson (2012b) who used the same gravel bed. The hydraulic roughness of the fixed gravel bed yielded a Darcy-Weisbach friction factor f = 0.031 to 0.045, corresponding to an equivalent sand bed roughness height k s = 3.4 mm (Docherty and Chanson, 2010).…”

Section: Iii3 Experimental Study Iii31 Facilitymentioning

confidence: 99%

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Effects of tidal bores on turbulent mixing: a numerical and physical study in positive surges

Simon

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Tidal bores are positive surges created by the flooding of tides inside estuaries and rivers. They propagate upstream in an estuary sometimes as several metre high waves. Tidal bores are fascinating phenomenon with some impact on the wildlife, the mixing and re-suspension of sediments, and river constructions. Field studies remain challenging due to the violent nature of some bores. Herein, the hydrodynamics of tidal bores was investigated in a complementary study with experimental measurements and numerical simulations of idealised models of tidal bores. While laboratory experiments offer an accurate way to measure the flow properties, numerical simulations provide rather detailed information on the hydrodynamics of bores. These simulations require detailed experimental data to accurately replicate the experiments and validate the numerical methods.Investigations were conducted at the University of Queensland in a large rectangular channel partially covered by a fixed gravel bed. The steady flow condition properties were investigated using a Pitot tube and acoustic Doppler velocimeters (ADVs). The unsteady flow conditions were obtained by the fast closure of a downstream gate, which led to an upstream propagating bore. Free surface characteristics were studied for several types of bores, from undular to breaking. Those measurements showed large free surface fluctuations during the bore passage in agreement with earlier findings. Velocity measurements were conducted at high frequency (200 Hz). In breaking bores, the ensemble averaged data exhibited large velocity reversals near the bed beneath the bore front and in its wake, whereas, in undular bores, a lesser deceleration was observed. The vertical velocity data trend closely followed the water depth time derivative for both breaking and undular bores. Overall, the velocity measurements displayed large velocity fluctuations during the passage of the bore which were believed to induce strong turbulent mixing. The turbulence was further investigated by a two point correlation technique to estimate both turbulent integral time and length scales. The turbulent integral length scales values were similar in the steady and unsteady flows, whereas the turbulent time scales were larger in the unsteady flow. The experiments were limited by the instrumentation since the ADV systems interacted with each other and lacked accuracy for measurements performed in the near vicinity of physical boundaries.A numerical investigation was then performed using the computational fluid dynamics (CFD) ii code Thétis developed in the I2M laboratory of the Université de Bordeaux. Numerical simulations reproduced experiments performed in laboratory prior to this study (Chanson, 2010a,b). The fluid was modelled by the Navier-Stokes equations in their incompressible two-phase form. The turbulence model used a large eddy simulation and the interface air-water was tracked by using a volume of fluid model. Two dimensional and three dimensional simulations were performed to study the comp...

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Mechanism for Sediment Transport at Tidal Estuaries Under Bore Formation

Dolgopolova

2020

Processes in GeoMedia—Volume I

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Sediment inception under breaking tidal bores

Cited by 14 publications

References 4 publications

Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat, West Indies

Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat, West Indies

Effects of tidal bores on turbulent mixing: a numerical and physical study in positive surges

Mechanism for Sediment Transport at Tidal Estuaries Under Bore Formation

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