Probabilistic description of grain resistance from simultaneous flow field and grain motion measurements

Bottacin‐Busolin, Andrea; Tait, Simon; Marion, Andrea; Chegini, Amir; Tregnaghi, Matteo

doi:10.1029/2007wr006224

Cited by 23 publications

(25 citation statements)

References 29 publications

(43 reference statements)

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“…Visually, it is diffi cult to assess if transport events coincide with high or low values of any of the seven variables. This attests to the fact that there are no unique sets of conditions under which particle are mobilized as observed by Bottacin-Busolin et al (2008). The following observations can be made: (1) transport events occur both at high or low streamwise velocity; (2) many transport events occur concomitantly to a positive vertical velocity; (3) high Reynolds shear stress values do not seem to be associated with transport events; (4) several transport events coincide with peaks in the streamwise and vertical normal stresses; (5) most events occur at rapid transitions in the streamwise and vertical fl ow velocities, thus hinting at the potential role of fl uid acceleration and deceleration on the bedload movement.…”

Section: Linking Mean and Turbulent Fl Ow Variables With Individual Tmentioning

confidence: 72%

Effects of turbulence on the transport of individual particles as bedload in a gravel‐bed river

Paiement-Paradis

Marquis

Roy

2010

Earth Surf Processes Landf

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This study investigates the association between mean and turbulent fl ow variables and the movement of individual particles in a gravel-bed river. The experimental design implemented in the Eaton-North River (Québec, Canada) is based on the simultaneous observations at a high temporal resolution of both particle movements as bedload using an underwater video camera and of the streamwise and vertical fl ow velocity components using a vertical array of three electromagnetic current meters (ECMs). The frequency and distance of displacement of particles larger than 20 mm that were sliding or rolling on the bed were measured from a 10 minutes long fi lm. Mean and turbulent fl ow properties obtained for periods without sediment transport are compared to those when particles were sliding and rolling. When particles are sliding, weak differences are present for the mean streamwise velocity and normal vertical stresses. Instantaneous Reynolds shear stresses are signifi cantly lower for sliding events which was not expected but could be explained by the important dominance of Quadrant 3 events (inward interactions). When particles are rolling, only the vertical normal stresses show a weak difference from those observed in the absence of transport but they tend to occur when Quadrant 2 (ejections) dominate the fl ow fi eld. For both sliding and rolling particles, vertical and/or streamwise fl uid accelerations show high magnitude values when compared to periods without transport. For sliding particles, streamwise acceleration is mostly negative and combines most of the time with a positive vertical acceleration. For rolling particles, streamwise and vertical acceleration are predominantly of opposite sign. These results suggest that fl uid acceleration or deceleration in the streamwise and vertical directions is affecting the pressure fi eld around particles. In this study, fl uid acceleration seems to play a more important role than Reynolds shear stress or normal stresses for bedload movements.

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Section: Linking Mean and Turbulent Fl Ow Variables With Individual Tmentioning

confidence: 72%

Effects of turbulence on the transport of individual particles as bedload in a gravel‐bed river

Paiement-Paradis

Marquis

Roy

2010

Earth Surf Processes Landf

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“…It has been demonstrated by others that some aspect of streamwise velocity strongly correlates with sediment entrainment transport, but that the cross products of velocity have a poorer relationship with sediment entrainment (Williams et al, 1989;Nelson et al, 1995;Papanicolaou et al, 2001;Schmeeckle and Nelson, 2003). For example, Bottacin-Busolin et al (2008) discovered that over half of the grain movements observed over a gravel bed were due to variations in the streamwise component of velocity, and only in a relatively small percentage of the cases (around one-tenth) were they characterised by changes in the cross-product of temporal fl uctuations in velocity. In simple terms, entrainment appears .…”

Section: Contributions To the Total Fluid Forcementioning

confidence: 96%

Examining the physical components of boundary shear stress for water‐worked gravel deposits

Cooper¹,

Tait²

2010

Earth Surf Processes Landf

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It is argued in this commentary that, in order to understand better the physical mechanisms that generate boundary shear stress over water-worked gravel beds, fl ow velocity data should be re-evaluated by spatial averaging the Reynolds equations to produce time-and space-averaged (double-averaged) momentum equations. A series of laboratory experiments were conducted in which the fl ow velocities were measured using a PIV system over two water-worked gravel deposits. Combined with detailed data on the bed surface topography and vertical porosity, the physical components of shear stress were obtained. This enabled the various momentum transfer mechanisms present above, within and at the interface of a porous, fl uvial deposit, to be quantifi ed. This included the examination of the relevant contributions of temporal and spatial fl uctuations in velocity and surface drag to the overall momentum transfer. It is demonstrated that double-averaging represents a logical framework for assessing the fl uid forces responsible for sediment entrainment and for investigating intragravel fl ow and sediment-water interface exchange mechanisms within the roughness layer in water-worked gravel deposits. By considering the physical components of shear stress and their relative sizes it was possible to provide a physically based explanation for existing observations of enhanced mobility of gravel-sand mixtures and the transfer of solutes into porous, gravel deposits. This analysis reveals the importance of obtaining co-located, high quality spatial data on the fl ow fi eld and bed surface topography in order to gain a physical understanding of the mechanisms which generate boundary shear stress.

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“…Bottacin-Busolin et al (2008) performed measurements at a level of shear stress just above the critical shear stress, so they were only able to characterise the lower range of critical entrainment velocities. Instead we have simulated the distribution of τ c using a discrete particle model first developed by McEwan and Heald (2001).…”

Section: Estimation Of Critical Shear Stressmentioning

confidence: 99%

Does flow variance affect bedload flux when the bed is dominated by grain roughness?

Cooper

2012

Geomorphology

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Probabilistic description of grain resistance from simultaneous flow field and grain motion measurements

Cited by 23 publications

References 29 publications

Effects of turbulence on the transport of individual particles as bedload in a gravel‐bed river

Effects of turbulence on the transport of individual particles as bedload in a gravel‐bed river

Examining the physical components of boundary shear stress for water‐worked gravel deposits

Does flow variance affect bedload flux when the bed is dominated by grain roughness?

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