The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers

Hassan, Marwan A.; Reid, Ian

doi:10.1002/esp.3290150807

Cited by 163 publications

(138 citation statements)

References 29 publications

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“…have been reported by Tait and Willetts [1992b] and, in somewhat similar experimental circumstances, by Hassan and Reid [1990]. Declining sediment transport in previous experiments has been ascribed to continued degradation of the bed and coarsening of the surface [e.g., Gessler, 1970].…”

Section: Experimental Observationssupporting

confidence: 56%

Stabilizing self‐organized structures in gravel‐bed stream channels: Field and experimental observations

Church¹,

Hassan²,

Wolcott³

1998

Water Resources Research

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317

359

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IntroductionMost alluvial stream channels change remarkably little over periods that can be as long as years or decades, even though they may be regularly subjected to sediment-transporting flows. Stream channels are stability-seeking entities. What we see is the product of a succession of changes; the morphology that persists is that which is most nearly stable in face of the usually imposed flows. Stability is gained when stream energy can be dissipated without the accomplishment of significant channel-deforming work, even though sediment transfer, including the exchange of sediment at the channel boundaries, may still occur. Energy-dissipating structures develop at all morphological scales within the channel, including the scales of channel pattern, pool and riffle, and sedimentary bed forms. However, the most basic level at which stability develops in gravel-bed channels is that of the granular boundary materials, the potentially mobile sediments themselves.Grains are entrained in stream channels when the force of water acting on the alluvial bed material overcomes particle inertia. Shields [1936] expressed the force balance at entrainment as a "mobility number," a function of the ratio of fluid shear stress exerted on the bed to (submerged) particle weight. [Gomez, 1993]. None of these factors eliminate the fundamental effect of particle weight. However, when particles become interlocked, the relative effect of particle weight becomes comparatively less dominant.• In gravel-bed streams with low rates of bed material transport, we have observed much more complex grain structures, which we call stone cells [cf. Gustavson, 1974]. The purpose of this paper is to describe these features, to obtain some phenomenological understanding of the conditions under which they develop and persist, and to explore their influence on the promotion of streambed stability. 2.Field Observations

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Section: Experimental Observationssupporting

confidence: 56%

Stabilizing self‐organized structures in gravel‐bed stream channels: Field and experimental observations

Church¹,

Hassan²,

Wolcott³

1998

Water Resources Research

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317

359

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“…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%

Occurrence of cluster microforms in mountain rivers

Strom

Papanicolaou

2008

Earth Surf Processes Landf

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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.

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“…La taille (Leopold et al, 1964 ;Hey, 1979 ;Bray, 1980Bray, , 1982Griffiths, 1981 ;Millar, 1999), la concentration (Morris, 1955 ;Nowell et Church, 1979 ;Raupach, 1981 ;Robert et al, 1992Robert et al, , 1993Robert, 1996 ;Smart, 1999), l'orientation (Wohl et Ikeda, 1998) et l'organisation spatiale (Hassan et Reid, 1990) des éléments de rugosité sont les variables le plus souvent utilisées pour caractériser l'effet des blocs et des amas de galets sur l'écoulement. À l'échelle d'un tronçon de cours d'eau, l'organisation spatiale des blocs et des amas de galets représente sans aucun doute l'une des variables les plus importantes puisqu'elle comprend à la fois la notion de concentration et celle de taille des particules.…”

Section: Introductionunclassified

Organisation morphologique des blocs et des amas de galets dans les cours d’eau à lit de gravier

Lamarre

Roy

2003

gpq

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Dans les cours d’eau à lit de graviers, les blocs et les amas de galets entraînent des changements de rugosité qui jouent un rôle important sur la variabilité spatiale du cisaillement exercé sur le lit, de la structure de l’écoulement et du transport des sédiments. Pourtant, peu de méthodes permettent de décrire l’organisation de ces éléments de rugosité du lit à l’échelle de la section de cours d’eau. Nous présentons deux méthodes d’échantillonnage qui permettent de quantifier l’organisation spatiale des blocs et des amas de galets sur quatre tronçons de rivière : la cartographie ponctuelle des blocs isolés et des amas de galets et la cartographie systématique de la topographie du lit. Les caractéristiques de l’organisation spatiale de ces éléments de rugosité sont quantifiées et comparées à celles de distributions aléatoires. Nous observons d’abord que la concentration des blocs isolés et des amas de galets, la distance qui les sépare et les caractéristiques des alignements composés de plusieurs éléments de rugosité sont semblables dans le cas des cours d’eau de même dimension. Ensuite, certaines caractéristiques de l’organisation spatiale des blocs et des amas de galets ressemblent à celles des distributions aléatoires. Nous proposons en discussion une interprétation dynamique de l’organisation spatiale des éléments de rugosité qui tienne compte de ces observations.Pebble clusters and large protuberant clasts such as boulders introduce a strong variability in the distribution of roughness in gravel-bed rivers and exert a significant influence on flow resistance and sediment transport. However, understanding the complex morphology of the bed at a reach scale is limited by the scarcity of sampling strategies to locate these roughness elements in the reach. In this paper, we present two sampling strategies to characterize the spatial organisation of boulders and pebble clusters in four river reaches. We have mapped 1) isolated boulders and pebble clusters and 2) bed topography at a high spatial resolution to compare the characteristics of the spatial organisation of these elements with those obtained from random distributions. We observed that the concentration of boulders and pebble clusters, the distance between neighbouring elements and the characteristics of transverse ribs are similar for reaches of the same width. Furthermore, some characteristics of the spatial organisation of the elements in a natural reach are similar to that of random distributions. A dynamic interpretation of the spatial organisation of bedforms that includes these observations is proposed.En los cauces formados por un lecho de grava los bloques de conglomerados de cantos rodados inducen cambios de rugosidad que juegan un papel importante en la variación espacial del corte ejercido sobre el lecho, de la estructura del escurrimiento y del transporte de los sedimentos. Sin embargo, pocos métodos permiten describir la organización de esos elementos de rugosidad del lecho a la escala de la sección del cauce. Se presentan aquí dos métodos d...

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The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers

Cited by 163 publications

References 29 publications

Stabilizing self‐organized structures in gravel‐bed stream channels: Field and experimental observations

Stabilizing self‐organized structures in gravel‐bed stream channels: Field and experimental observations

Occurrence of cluster microforms in mountain rivers

Organisation morphologique des blocs et des amas de galets dans les cours d’eau à lit de gravier

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