Simulations of cobble structure on a gravel streambed

Tribe, Selina; Church, Michael

doi:10.1029/98wr01141

Cited by 27 publications

(27 citation statements)

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“…Les alignements présentent différents stades d'évolution. Ils traversent le chenal d'une rive à l'autre selon une orientation oblique et, moins souvent, perpendiculaire à l'écoulement (Tribe et Church, 1999). Leur destruction partielle peut entraîner la pré-sence d'alignements scindés en deux parties qui persistent près des berges (De Jong et Ergenziner, 1995).…”

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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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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“…As the result of grain-grain interference during tractive transport of sediment over the bed, the resident material becomes arranged into recognizable structures [Johnston, 1922;Laronne and Carson, 1976] that increase the reluctance of individual grains to move [Brayshaw et al, 1983], reduce the bed material transport, and reinforce the overall stability of the channel bed [Church et al, 1998]. The development of bed structures has been investigated experimentally by Church et al [1998] under the condition of zero sediment influx, and the nature of the grain-grain interaction has been studied computationally by Tribe and Church [1999]. Here we report the extension of our experiments to the condition of low rates of bed material influx over an already structured bed, the usual condition of bed material transport in most gravel bed channels in nature.…”

Section: Introductionmentioning

confidence: 99%

Experiments on surface structure and partial sediment transport on a gravel bed

Hassan¹,

Church²

2000

Water Resources Research

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144

156

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Abstract. Eight flume experiments were conducted to study the development of bed surface texture and structure in the presence of partial bed material transport. The experiments have two phases, a no-feed degradational phase followed by a feeding phase. A surface structure of irregular, reticulate stone nets and clusters was developed before sediment feeding commenced. Bed load transport equaled or slightly exceeded the fed supply, except at the highest feed rate. The bed structure was maintained, but bed surface texture fined with increasing sediment load. The two phenomena may coexist because the largest grains on the bed moved only very sporadically. The actual sediment transport rates were much less than the expected rate calculated from the ratio of bed surface grain size to transported grain size. The difference reflects the increase in bed stability introduced by the bed structure. Between 17% and 47% of the bed shear stress is estimated to be carried by the structure, <4% being absorbed by the load, while the bed grains carried the balance of the stress. Bed material transport is exceedingly sensitive to bed surface structure and grain size, which raises concerns about the realizable precision of grain size measurements and characterization of the structure.

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“…For simplification only one particle at a time is permitted to move and interact with the bed (cf. Tribe and Church, 1999). During each run a specified number of movements are simulated.…”

Section: Methodsmentioning

confidence: 99%

“…All distributions were truncated at 4 mm because, (1) we are interested in modelling the coarse fractions, (2) there is assumed to be no interaction between large sizes and those finer than 4 mm, and (3) this covers the size range of tracers used in Harris Creek Church, 1992, 2001). Further information on the Harris Creek prototype can be found in Church et al, (1998), Tribe and Church (1999) and Church (2000, 2001).…”

Section: Model Developmentmentioning

confidence: 98%

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Simulation of individual particle movement in a gravel streambed

Malmaeus

Hassan

2002

Earth Surf Processes Landf

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A two-dimensional simulation model of travel distances of individual particles in a gravel-bed river is presented. The model is based on a number of rules, which include particle size, entrainment, trajectory, distance of movement and entrapment. Particle interactions are controlled by resistance fields defined about each obstacle and critical elevation defined in the model. Resistance fields, particle dropping and critical elevation rules control particle interactions. The interaction rules cause the particles to develop pebble clusters, stone cells and transverse structures (transverse ribs). The simulated travel distances of individual particles are consistent with reported field results. Individual particle travel distances were simulated using two different models; one without interactions between the individual particles and the stationary bed and one with interactions. The case without interactions demonstrates the random nature of sediment transport, and narrow ranges of travel distances. Wider ranges of travel distances, similar to those for natural situations, were obtained for the cases with interactions. The more intense the interaction between the mobile stones and the stationary ones, the wider the range of distances of travel for a given particle size. Modelling the mean travel distance yielded a result similar to that published previously, which was based on empirical data. Well developed bed-surface structures were obtained for relatively poorly sorted sediment with intense interactions between particles. Transverse structures developed when relatively large particles were allowed to move.

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Simulations of cobble structure on a gravel streambed

Cited by 27 publications

References 11 publications

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

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

Experiments on surface structure and partial sediment transport on a gravel bed

Simulation of individual particle movement in a gravel streambed

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