Bed microtopography and entrainment thresholds in gravel-bed rivers

Brayshaw, Andrew C.

doi:10.1130/0016-7606(1985)96<218:bmaeti>2.0.co;2

Cited by 100 publications

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“…boulders and cobbles). Pebbles clusters and individual substrate particles form an important microtopography in gravel-bed rivers (Brayshaw, 1985) and create substrate heterogeneity. The dominance of trapping structures in step-pool reaches suggests an abundance of available flow refugia for organisms during high flow events.…”

Section: Flow Refugia and Invertebrate Diversitymentioning

confidence: 99%

“…Small-scale bedforms described as pebble clusters (e.g. Brayshaw et al, 1983;Brayshaw, 1984;Billi, 1988) represent an important microhabitat and are the main type of microtopography in gravel-bed rivers (Brayshaw, 1985). These 'pebble clusters' represent a general term for bed obstacles (typically boulders and cobbles) that protrude above the water surface with a stoss-side accumulation of large pebbles and a wake deposit of finer particles (Robert, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Characterization of hydraulic habitat and retention across different channel types; introducing a new field-based technique

Milner

Gilvear

2012

Hydrobiologia

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Understanding the interactions between physical habitat and aquatic biodiversity has become a key research objective in river management. River research and management practitioners are increasingly seeking new methodologies and techniques for characterizing physical habitat heterogeneity. The physical biotope has been widely employed as the standard mesoscale unit in river surveys. However, few surveys have quantified the combined physical heterogeneity at the meso- and microscale scale via a single technique. This paper describes a new field methodology for assessing variations in hydraulic habitat and retention across different channel types (e.g. step-pool, bedrock, plane-bed and pool-riffle). Hydraulic habitat and retention was measured by timing 100 flow tracers across a 100-m stream length, and recording the types of trapping structures. The pattern of flow tracers and retention varied significantly between channel types and structures. Rocks (boulders and cobbles) were more important retentive structures than eddies and snags (woody material and vegetation). The results indicate the importance of a diverse hydraulic environment, woody material and channel substrate character in increasing physical heterogeneity within a stream reach. The findings suggest that the field methodology may be an effective tool to assess differences in physical heterogeneity pre and post river restoration activities

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Section: Flow Refugia and Invertebrate Diversitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterization of hydraulic habitat and retention across different channel types; introducing a new field-based technique

Milner

Gilvear

2012

Hydrobiologia

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“…Les blocs isolés et les amas de galets constituent les principaux éléments de la rugosité du lit (ci-après nommés éléments de rugosité) qui influencent la variabilité spatiale de la résistance à l'écoulement et qui stabilisent la surface (Dal Cin, 1968 ;Brayshaw, 1985 ;Naden et Brayshaw, 1987). Dans cette perspective, la connaissance de ces arrangements sédimentologiques mène à une meilleure compréhension de la dynamique du transport des sédiments, de l'écoulement et de la stabilité des lits de rivières.…”

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 first supports the idea that clusters provide stability to the bed, and hence delay sediment entrainment by acting as a sink for incoming sediment (Brayshaw, 1984(Brayshaw, , 1985Hassan and Reid, 1990;Reid et al, 1992;Church et al, 1998;. The second considers clusters to be a less significant factor in channel stability or sediment transport (Billi, 1988;De Jong, 1991).…”

Section: Introductionmentioning

confidence: 54%

The role of hydrologic processes and geomorphology on the morphology and evolution of sediment clusters in gravel-bed rivers

2010

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Bed microtopography and entrainment thresholds in gravel-bed rivers

Cited by 100 publications

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Characterization of hydraulic habitat and retention across different channel types; introducing a new field-based technique

Characterization of hydraulic habitat and retention across different channel types; introducing a new field-based technique

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

The role of hydrologic processes and geomorphology on the morphology and evolution of sediment clusters in gravel-bed rivers

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