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Résultats de la recherche (48 résultats)

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  • The dominance of dispersion in the evolution of bed material waves in gravel-bed rivers
  • This paper summarizes recent theoretical models, experiments and field studies that have been designed specifically to measure relative rates of dispersion and translation of bed material waves. In considering uniform channels only, and also
  • in disregarding exchanges of sediment between a channel and its floodplain, 2 factors influence wave behaviour : interactions between flow, wave topography and bed load transport; and relative particle sizes of input sediment and pre-existing bed material
  • . The results indicate that dispersion dominates the evolution of bed material waves in gravel-bed channels.
  • 2001
  • Visual characterization technique for gravel-cobble river bed surface sediments; validation and environmental applications contribution to the programme of CIRSA (Centre Interuniversitaire de Recherche sur le Saumon Atlantique)
  • Canada ; Ecosystem ; Fish ; Fluvial processes ; Grain size distribution ; Gravel ; Habitat ; Quebec ; Research technique ; River bed ; Sampling ; Stream
  • This study proposes a useful alternative visual technique to characterize the surface substrate (size and distribution) over an expanse of a gravel-bed river. The paper is divided into 4 sections : a brief review of bed sediment sampling techniques
  • ; an explanation of the methodology and training protocol used for the visual estimation of a river bed surface sediment size distribution; the error estimation linked to this technique and a comparison with common surface sampling techniques (grid sampling
  • 2001
  • Thresholds of particle entrainment in a poorly sorted sandy gravel-bed river
  • This paper presents an analysis of a new data set on threshold conditions for bed material entrainment in the poorly sorted sandy gravel-bed of the Arbúcies River (NE Spain), an interesting example of a perennial to ephemeral transitional
  • 2001
  • Computational fluid dynamics modelling of boundary roughness in gravel-bed rivers : an investigation of the effects of random variability in bed elevation
  • over 2 contrasting gravel beds. The aims of this study are : to assess the performance of the CFD model; to identify the limitations of the conventional wall function approach; to explore the potential for modelling intermediate-scale roughness effects
  • using a random elevation model, and to address the wider implications of these results for the application of CFD models to natural gravel-bed channels.
  • 2001
  • Determination of the sediment transport in an armoured gravel-bed river
  • -discharge (Qb/Q) relationships are determined by local bed-load transport in the Common Meuse. The survey data in the Common Meuse were analysed with a geographical information system (GIS) (ARC-INFO) to produce maps of the river-bed level. The subtraction
  • of maps of bed levels in different years results in a map with spatial distributions of erosion and sedimentation.
  • 2001
  • Carrying capacity ; Dune ; Experimentation ; Fluvial processes ; Longitudinal section ; Model ; Ripple-mark ; River bed ; Runoff ; Stream flow ; Turbulence
  • Flume experiments were conducted on different bed stages across the ripple-dune transition. As flow velocity increases, an initially flat bed surface (made of fairly uniform sandy material) is gradually transformed into a two-dimensional rippled bed
  • . With further increase in velocity, two-dimensional ripples are replaced by irregular, linguoid ripples. As the average velocity necessary for the ripple-dune transition to occur is imposed on the bed surface, these non-equilibrium linguoid ripples are further
  • transformed into larger, two-dimensional dunes. For each of these stages across the transition, a concrete mould of the bed was created and the flow structure above each fixed bed surface investigated.
  • 2001
  • Effective discharge and gravel-bed rivers
  • Rivers with constraints on the mobility of bed material, typically armoured channels with steeper than average relationship of bedload discharge to water discharge, may have an effective discharge occuring at higher stages and greater recurrence
  • intervals than bankfull discharge. Bedload discharges were measured at 5 snow-melt dominated, gravel-bedded rivers in the northern Rocky Mountains, USA. Data indicate that, as the exponent of the bedload rating increases from typical to more steep values
  • 2001
  • Three-dimensional flow structure around small-scale bedforms in a simulated gravel-bed environment
  • Gravel ; Model ; River bed ; Runoff ; Simulation ; Stream ; Stream flow ; Turbulence
  • This paper presents high-resolution three-dimensional data illustrating the effects of pebble clusters on turbulent flow characteristics in a simulated gravel-bed environment. Past research has tended to focus on only 2 flow components : downstream
  • ) model and will elucidate more explicitely bed-flow interactions in gravel-bed environments.
  • 2001
  • Adjustment of mainstream - Tributary relation upstream from a reservoir : an example from the Laohahe River, China
  • Base level ; Beijing ; Carrying capacity ; Channel geometry ; China ; Fluvial dynamics ; Hydraulic works ; Impact ; River bed ; Sediment load ; Sedimentation ; Stream
  • Based on data from the Laohahe River and the Yangchangzihe River, its tributary, both located above the Honshan Reservoir, effort has been made to reveal the response of tributary channel to the rising base-level induced by the reservoir
  • construction and the sedimentation in the river mainstream. This paper also discusses the feedback from the tributary to the channel adjustment of the river mainstream. Due to the strong sedimentation in the river mainstream, the response of channel adjustment
  • 2001
  • The sensitivity of Scottish rivers and upland valley floors to recent environmental change
  • Atmospheric circulation ; Flood ; Global change ; Land use ; Nineteenth Century ; River bed ; Scotland ; Sensitivity analysis ; Stream ; United Kingdom ; Valley floor evolution
  • This paper examines the stability of river channels and their associated valley floors in the uplands of Scotland since 1750. Changes in global-scale atmospheric circulation patterns during this period have resulted in regionally district flood-rich
  • and flood-poor periods with potential geomorphic impacts. Changes in the planform of 9 active rivers in the piedmont zone of upland Scotland are examined from series of rectified maps and aerial photographs at scales close to 1:10 000. Differences
  • in geomorphic history, land use and degree of slope-channel coupling are identify as the likely causes of marked differences in the behaviour of active rivers in Scotland and northern England over the last 250 years.
  • 2001
  • Canada ; Channel geometry ; Hydraulic works ; Ontario ; River bed ; Roughness ; Spatial analysis ; Stream ; Stream flow ; Turbulence ; Wood
  • The aim of this study is to identify the spatial extent of flow disturbance caused by coarse woody debris positioned normal to the flow between 75° and 105°to the downstream flow direction. A reprsentative reach of the Pine River, Ontario, was used
  • for intensive study, and results were compared to similar obstructions elsewhere on the same river (n = 48) as well as on another system (Wilmot Creek, n = 1066) with a high volume of woody debris.
  • 2001
  • Bank erosion ; Channel geometry ; Experimentation ; Mississippi ; Model ; River bed ; Sand ; Stream ; United States of America
  • This paper presents the results of a movable-boundary, distorted, Froude-scaled hydraulic model based on Abiaca Creek, a sand-bedded channel in northern Mississippi. The model was used to examine the geomorphic and hydraulic impact of simplified
  • 2001
  • Riparian vegetation and island formation along the gravel-bed Fiume Tagliamento, Italy
  • Alps (The) ; Braided channel ; Channel geometry ; Gravel ; Hydrological regime ; Italy ; Model ; Riparian vegetation ; River bed ; Stream ; Wood
  • 2001
  • Channel bed steps and pool shapes along Soda Creek, Three Sisters Wilderness, Oregon
  • Lithology ; Longitudinal section ; Oregon ; River bed ; Slope gradient ; Stream ; United States of America ; Volcanic rock
  • 2001
  • Carrying capacity ; Experimentation ; Fluvial hydrology ; Gravel ; Longitudinal section ; Model ; River bed ; Roughness ; Runoff ; Shear stress ; Stream ; Stream flow ; Turbulence
  • be placed on the very near-bed region, the shear stress estimated from average profiles, the turbulence intensity profiles, and the implications of the findings to bed load transport and flow resistance prediction equations.
  • 2001
  • Toward a practical method for estimating sediment-transport rates in gravel-bed rivers
  • 2001
  • Channel geometry ; Classification ; Economic activity ; Fluvial processes ; Human impact ; River bed ; Structural stability
  • 2001
  • Ardenne ; Belgium ; Biology ; Earth surface processes ; Human impact ; Hydrodynamics ; Impact study ; River bed ; River management ; Stream ; Wallonie
  • 2001
  • Canal ; Environmental conservation ; Fluvial processes ; Germany ; Landscape ; Navigation ; River bed ; River management ; Traffic
  • 2001
  • Carrying capacity ; Channel geometry ; England ; Gravel ; Northumberland ; River bed ; Sediment load ; Shear stress ; Stream ; United Kingdom
  • this issue by providing velocity and boundary shear stress data over a range of discharges from a sequence of 4 pools and 3 riffles in the River Rede, Northumberland.
  • 2001