Undular and breaking bores on fixed and movable gravel beds

Khezri, Nazanin; Chanson, Hubert

doi:10.1080/00221686.2012.686200

Cited by 30 publications

(25 citation statements)

References 25 publications

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“…A transient velocity recirculation was observed beneath breaking bores, but not for undular bores. This has been confirmed in some other studies (Chanson, 2010b;Docherty and Chanson, 2012;Khezri and Chanson, 2012c). After the bore passage, the turbulence in terms of Reynolds stress was shown to be larger than in the initial steady flow, and different between breaking and undular bores (Koch and Chanson, 2005).…”

Section: Ii4 Experimental Studies Of Positive Surgessupporting

confidence: 73%

“…The present data are ensemble-averaged A comparison between present and earlier data on smooth bed suggested that the wave amplitude and steepness were slightly smaller on rough bed for a given Froude number. The observation was supported by the data of Chanson (2010b) and Docherty and Chanson (2012) on rough beds, but not by the data set of Khezri and Chanson (2012c) also on rough bed ( Figure IV.20). Note that the maximum in wave amplitude and wave steepness, corresponding to the propagation of a bore with a breaking roller, was reached for different Froude numbers depending upon the study.…”

Section: Iv332 Free Surface Properties Based Upon Froude Number Cosupporting

confidence: 69%

“…Without a slope, only undular bore could be performed. The fixed gravel bed was located from x = 0.59 m to 9.15 m (section III.3) similarly to setting in Docherty and Chanson (2012) and Khezri and Chanson (2012c). For all investigated flow conditions, the flow was supercritical upstream of the fixed gravel bed.…”

Section: Iv2 Basic Steady Flow Propertiesmentioning

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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Section: Ii4 Experimental Studies Of Positive Surgessupporting

confidence: 73%

Section: Iv332 Free Surface Properties Based Upon Froude Number Cosupporting

confidence: 69%

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

Simon

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“…Due to the large velocity variations, it can be concluded that the turbulence generation and fluid particle mixing are also much more intensive in the breaking bore, as compared with the undular bore. This phenomenon has been experimentally disclosed by Khezri and Chanson (2012). In general, the SPH computations satisfactorily demonstrated both types of the tidal bore velocity structures and this is due to the fact that the mesh-free SPH approach has the capability of treating the free surfaces of large deformation without the numerical diffusion and thus can realistically reproduce these violent flows.…”

Section: Fig 2 Laboratory Bore Flume and Measurement Facilitymentioning

confidence: 73%

“…In a recent pioneering work, Khezri and Chanson (2012) found that in the undular bore experiment, the sediment movement was almost negligible, while some strong sediment motions were observed beneath the breaking bore. In a practical field, this can have a major impact on the sediment processes in the estuarine zone.…”

Section: Undular and Breaking Bore Flows In An Unconfined Open Channelmentioning

confidence: 99%

SPH modeling of tidal bore scenarios

Liu

Shao

et al. 2014

Nat Hazards

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The paper presented a Smoothed Particle Hydrodynamics (SPH) method to study the three-dimensional (3D) tidal bore scenarios. The SPH method is a mesh free particle modeling technique that can track the large deformation of free surfaces in a straightforward and accurate way. Two benchmark cases of the tidal bore propagation were computed and compared with the experimental results. The first one is related to the undular and breaking bores in a regular open channel and the second one considers the undular bore passing through the contraction of bridge piers. Physical laboratory experiments have also been carried out to validate the numerical investigations. The comparisons of both the free-surface profile and velocity field demonstrated that the SPH technique could provide a very promising tool to simulate tidal bore phenomena in engineering practice. The work is the first to systematically explore the potentials of mesh-free SPH modeling approach in predicting the tidal bore features under 3D flow conditions.

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Fluid flow and sediment entrainment in the Garonne River bore and tidal bore collision

Keevil

Chanson

Reungoat

2015

Earth Surf Processes Landf

Self Cite

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Abstract:A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well-defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated 'backward' to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. 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. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters.

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Undular and breaking bores on fixed and movable gravel beds

Cited by 30 publications

References 25 publications

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

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

SPH modeling of tidal bore scenarios

Fluid flow and sediment entrainment in the Garonne River bore and tidal bore collision

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