Effects of a pebble cluster on the turbulent structure of a depth-limited flow in a gravel-bed river

Buffin‐Bélanger, Thomas; Roy, Alain

doi:10.1016/s0169-555x(98)00062-2

Cited by 148 publications

(128 citation statements)

References 25 publications

Supporting

Mentioning

109

Contrasting

Unclassified

Order By: Relevance

“…Ainsi, au moment où le fort mouvement de retour se produit, une structure à faible vitesse passe au-dessus de l'obstacle. Ces observations rejoignent également la fréquence d'échappement de 1 événement par 5 secondes mesurée par BUFFIN-BÉLANGER et ROY (1998) à l'aval du même obstacle ( figure 12 dans BUFFIN -BÉLANGER et ROY, 1998). De plus, BUFFIN-BÉLANGER ef al.…”

Section: -Un Modele D'interactions Entre Structures Turbulentesunclassified

“…dans ces environnements, les structures d'échappement représentent le premier mécanisme responsable de la résistance à l'écoulement (CLIFFORD ef al., 1992 ;ROBERT ef a/., 1996 ;BUFFIN-BÉLANGER et ROY, 1998 Les structures à grande échelle sont des portions de fluide rapide entrecoupées par des portions de fluide plus lent qui occupent toute la tranche de l'écoulement. La figure 1b illustre en deux dimensions le passage de ces portions de fluide à partir d'un échantillonnage des vitesses longitudinales instantanées à trois positions dans un écoulement sur lit de graviers.…”

Section: -Introductionunclassified

See 1 more Smart Citation

Interactions entre les structures d'échappement et les structures à grande échelle dans l'écoulement turbulent des rivières à lit de graviers

Buffin‐Bélanger¹,

Roy²,

Levasseur³

2005

rseau

View full text Add to dashboard Cite

Dans les rivières graveleuses, il est établi que les structures d'échappement formées dans la zone de recirculation à l'aval d'amas de galets génèrent d'intenses échanges turbulents. Le mécanisme responsable de l'échappement demeure par contre mal connu. Peu d'études sur la dynamique des structures d'échappement ont été réalisées dans des écoulements où le nombre de Reynolds est élevé comme c'est le cas en rivières. De plus, les connaissances actuelles ne tiennent pas compte des découvertes récentes sur la turbulence en rivière à lit de graviers où on a observé des structures de forte et de faible vitesse occupant toute la profondeur de l'écoulement et pouvant durer plusieurs secondes. Ces structures à grande échelle devraient jouer un rôle sur le mécanisme d'échappement étant donné l'influence de la vitesse ambiante sur la dynamique de la zone de recirculation. Nous rapportons les résultats de deux expériences originales sur les liens dynamiques entre les structures à grande échelle et le mécanisme d'échappement en aval d'un amas de galets. La première expérience repose sur l'analyse de corrélations croisées entre des séries de vitesses obtenues au sommet et à l'aval proximal d'un amas de galets. Les résultats montrent que les fortes fluctuations dans le sens de l'écoulement au sommet de l'obstacle sont liées, quelques instants plus tard, à de fortes fluctuations vers l'amont dans la zone de recirculation. La seconde expérience utilise la visualisation des structures d'échappement et la mesure simultanée des vitesses de l'écoulement. L'analyse combinée des images vidéo et de séries de vitesse suggère une relation entre le passage des structures à grande échelle et les manifestations de l'échappement. Ces résultats nous permettent de présenter un modèle où, lors du passage d'un front de haute vitesse, une structure d'échappement se développe et prend de l'expansion vers le lit et vers la surface en se propageant vers l'aval alors que, lors du passage d'un front de faible vitesse, elle s'élève vers la surface de manière plus cohérente. Cette étude propose un nouveau mécanisme d'échappement et révèle le rôle que joue la structure de l'écoulement ambiant sur le développement de structures dans les cours d'eau à lit graveleux.The flow structure in a gravel-bed river is closely related to the presence of protruding clasts and of pebble clusters. It is well known that shedding motions from the lee side of large clasts and clusters are a recurrent process that explains the strong exchanges of momentum in river flows. However, shedding has yet to be fully characterised for high Reynolds number flows such as those found in gravel-bed rivers. Moreover, our current understanding of shedding mechanisms does not include the recent discovery that large-scale flow structures in the form of high- and low-speed wedges occupy the entire flow depth over a gravel-bed river. From two original experiments, this paper investigates the influence of these wedges on the nature of shedding in the lee of a pebble cluster. The interactions b...

show abstract

Section: -Un Modele D'interactions Entre Structures Turbulentesunclassified

Section: -Introductionunclassified

Interactions entre les structures d'échappement et les structures à grande échelle dans l'écoulement turbulent des rivières à lit de graviers

Buffin‐Bélanger¹,

Roy²,

Levasseur³

2005

rseau

View full text Add to dashboard Cite

show abstract

“…Clusters have been observed to have an impact on the local dynamics of gravel bed rivers by introducing perturbations from a non-clustered state in bed stability Wittenberg and Newson, 2005), downstream particle movement (Billi, 1988), bedload transport rates (Strom et al, 2004), overall flow resistance (Hassan and Reid, 1990;, and local flow field characteristics (Buffin-Bélanger and Roy, 1998;Lawless and Robert, 2001;Strom et al, 2007b). In addition to studying the local dynamic environment created by clusters, it is also of interest to understand the conditions that are conducive to cluster formation within a stream reach and/or stream-network; such knowledge would be analogous to our understanding of the conditions that induce particular types of sand bedforms (e.g., Simons and Richardson, 1961).…”

Section: Introductionmentioning

confidence: 99%

“…In regard to location, clusters have been noted to occur on bars and, in some cases, in the main channel of streams with gravel and cobble size sediment (Brayshaw, 1984;Billi, 1988;de Jong, 1991de Jong, , 1995Reid and Hassan, 1992;Buffin-Bélanger and Roy, 1998;Wittenberg, 2002;Wittenberg and Newson, 2005). When present in the bed, it has been reported that cluster frequency is positively related to the d 90 of the bed material and the sorting index (Wittenberg et al, 2007), and that cluster to cluster spacing is likely proportional to the size of the largest particle in the cluster and inversely proportional to local channel slope (Strom and Papanicolaou, 2008).…”

Section: Introductionmentioning

confidence: 99%

Occurrence of cluster microforms in mountain rivers

Strom

Papanicolaou

2008

Earth Surf Processes Landf

View full text Add to dashboard Cite

The occurrence of cluster microforms in natural rivers is examined using data collected from three mountain streams. The study was conducted under the premise that the occurrence of clusters is strongly tied to local reach-scale conditions, and that prediction of clustered sites therefore can be made through identification of particular reach conditions that are conducive to cluster development. For the study, reach-scale variables were measured at 50 sites and the presence or absence of clusters at each of these sites was recorded. A statistical analysis using logistic regression was performed to examine the correlation between the occurrence of clusters and various combinations of reach-scale parameters. It was found that clustering was best predicted by the bankfull channel width scaled with the d 84 of the bed sediment, w/d 84 , and the non-dimensional parameter wQ 2 /gd 6 84 . It is thought that these variables work best at predicting the presence of clusters because they are descriptive of the reach hydraulic and sedimentary conditions and work well at discriminating between reach morphology types. It was found that clustering was most strongly tied to riffle-pool type reaches. Observations from this study suggest that clusters can be described as bed features that form out of the structural organization of grains in cobble-size sediment within depositional mountain reaches, for which the majority of the sediment can become mobilized by yearly peak flows.

show abstract

“…The size of the eddies generated by individual boundary protuberances scales, typically, with the dimension of the protruding elements. Examples of boundary singularities and irregularities in rivers causing eddy generation include sediment clusters or boulders protruding from the riverbed [submerged (Buffin-Bélanger and Roy 1998;Buffin-Bélanger et al 2000;Franca 2005b) or emerging (Tritico and Hotchkiss 2005)], high relative roughness riverbeds (Baiamonte et al 1995;Katul et al 2008), vegetation patches (Tanino and Nepf 2008;Siniscalchi et al 2012;Sukhodolova and Sukhodolov 2012;Ricardo 2014), wood debris or remains of organic elements (Shields et al 2004;Blanckaert et al 2014).…”

Section: Energy-based Description Of Processesmentioning

confidence: 99%

Turbulence in Rivers

Franca

Brocchini

2015

Rivers – Physical, Fluvial and Environmental Processes

View full text Add to dashboard Cite

The study of turbulence has always been a challenge for scientists working on geophysical flows. Turbulent flows are common in nature and have an important role in geophysical disciplines such as river morphology, landscape modeling, atmospheric dynamics and ocean currents. At present, new measurement and observation techniques suitable for fieldwork can be combined with laboratory and theoretical work to advance the understanding of river processes. Nevertheless, despite more than a century of attempts to correctly formalize turbulent flows, much still remains to be done by researchers and engineers working in hydraulics and fluid mechanics. In this contribution we introduce a general framework for the analysis of river turbulence. We revisit some findings and theoretical frameworks and provide a critical analysis of where the study of turbulence is important and how to include detailed information of this in the analysis of fluvial processes. We also provide a perspective of some general aspects that are essential for researchers/ practitioners addressing the subject for the first time. Furthermore, we show some results of interest to scientists and engineers working on river flows.

show abstract

Effects of a pebble cluster on the turbulent structure of a depth-limited flow in a gravel-bed river

Cited by 148 publications

References 25 publications

Interactions entre les structures d'échappement et les structures à grande échelle dans l'écoulement turbulent des rivières à lit de graviers

Interactions entre les structures d'échappement et les structures à grande échelle dans l'écoulement turbulent des rivières à lit de graviers

Occurrence of cluster microforms in mountain rivers

Turbulence in Rivers

Contact Info

Product

Resources

About