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Résultats de la recherche (173 résultats)

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  • Flow resistance in alluvial channels
  • Applied hydrology ; Flood ; Flow resistance ; River bed ; Roughness ; Sediment transport ; Stream ; Stream flow ; Turbulence
  • Significant progress has been made towards predicting flow resistance (and therefore velocity) for a given discharge. Different types of equations have been shown to provide reasonably good estimates in specific environments. Major difficulties
  • transport would ultimately provide valuable information and improved knowledge on both flow resistance processes and applications (predictions).
  • 2011
  • Czech Republic ; Discharge ; Floodplain ; Hydrology ; Lužnice river ; Piezometric level ; Spatial variation ; Stream ; Stream flow ; Surface water ; Temporality ; Underground water
  • This paper presents preliminary results of an assessment of the groundwater – surface water (GW-SW) interaction processes of the Lužnice River floodplain during a selected time period, comprising high and low stream flow. It analyses various events
  • that reflect the spatial and temporal variations in water flows to and from the floodplain. The results indicate that observed groundwater levels are closely associated with the river flows and the assessed reach was gaining most of the time. - (EN)
  • 2011
  • Magnitude and frequency relations of bankfull flows and bed-material entrainment in the Llano River watershed, Central Texas, USA
  • Carrying capacity ; Channel geometry ; Flood ; Peak discharge ; Sediment transport ; Stream ; Stream flow ; Texas ; United States of America ; Watershed
  • Bankfull channel geometry and bed-material entrainment are examined in the Llano River watershed in central Texas, which is characterized by mixed alluvial-bedrock boundaries and a highly variable flow regime. Field data, including cross-section
  • surveys and sediment samples from 17 sites, are coupled with one-dimensional hydraulic models and flood-frequency analyses to compute recurrence intervals of bankfull and entrainment conditions. Recurrence intervals of flows that entrain median-sized bed
  • material are consistently less than 1 year, whereas flows that define bankfull morphology range from 1 to 4 years (median of 1.75 years). Recurrence intervals of flows responsible for incipient entrainment of relatively coarse bed material are typically
  • less than 1.5 years, but complete mobilization of this size fraction occurs less frequently than bankfull flows.
  • 2011
  • A rational sediment transport scaling relation based on dimensionless stream power
  • Carrying capacity ; Concept ; Hydrodynamics ; Sediment transport ; Shear stress ; Stream ; Stream flow
  • The AA. derive a scaling relation that describes how externally imposed changes in either magnitude of sediment load or available discharge can be accommodated by changes in the channel configuration, described by the energy gradient, mean flow
  • depth, characteristic grain size and a parameter describing the effect of bed surface structures on grain entrainment. Therefore they derived an empirical transport function relation relating E to dimensionless stream power using data from a wide range
  • to the transfer of momentum from the fluid to the bed material (described by dimensionless stream power).
  • 2011
  • An experimental study of discharge partitioning and flow structure at symmetrical bifurcations
  • Bifurcation ; Channel geometry ; England ; Experimental catchment ; Leeds ; Model ; Runoff ; Stream ; Stream flow ; United Kingdom ; Yorkshire
  • , bifurcation flume models. The aims of the paper are to identify and to detail the partitioning of fluid, characterize the flow structures through the bifurcation model and to ascertain the key controls on the generation of flow structures at, and downstream
  • 2011
  • Discharge ; Flood ; Fluvial erosion ; Geotechnics ; Model ; Numerical model ; River bed ; Scouring ; Stream ; Stream flow
  • A modelling approach is presented to predict local scour under time varying flow conditions. The model is based on a number of hypotheses concerning the characteristics of the flow hydrograph, the temporal evolution of the scour and the geometry
  • of the scour hole. A key assumption is that, at any time, the scour depth evolves at the same rate as in an equivalent steady flow. Experimental data are presented that show the scour hole development downstream of bed sills due to flood hydrographs follow
  • in the rising limb of the flow hydrograph. This suggests that the underlying assumptions used in the modelling approach are appropriate.
  • 2011
  • Flow modelling in gravel-bed rivers: rethinking the bottom boundary condition
  • England ; Grain size distribution ; Gravel ; Model ; River bed ; Roughness ; Simulation ; Stream ; Stream flow ; United Kingdom
  • -resolution topography. The results show the ability of the model to capture the spatially-averaged flow field and, thus, illustrate its potential for representing flow processes in natural gravel-bed rivers. Finally, practical data requirements
  • 2011
  • Bedform response to flow variability
  • Colorado ; Experimentation ; Fluvial geomorphology ; Forecast ; Numerical model ; River bed ; Sediment transport ; Stream ; Stream flow ; United States of America
  • In this paper, results of the Giri and Shimizu (2006) model are compared with laboratory data on bedform response to time-varying flows that produce changes in bedform morphology without total removal (so-called washout) of bedforms. The goal
  • of the research presented herein is to assess this method for making predictions of bedform behavior in time-varying flows and to try to identify aspects of the problem that need further research to develop this and similar methods into practical predictive tools
  • 2011
  • Experimental analysis of cross-sectional flow motion in a large amplitude meandering bend
  • Bank erosion ; Channel geometry ; Cross section ; Experimentation ; Hydrodynamics ; Meander ; Stream ; Stream flow ; Turbulence
  • Experiments have been carried out in a laboratory meandering channel of large amplitude, over a deformed-rigid bed, for 2 values of the width-to-depth ratio. The three-dimensional flow velocity field has been measured in detail at 5 cross-sections
  • , almost equally spaced along the channel reach between 2 consecutive apex sections. The measurements have been carried out on a fine grid by an acoustic Doppler velocity profiler. The distributions of the cross-sectional flow and turbulent kinetic energy
  • 2011
  • Flow structures at an idealized bifurcation : a numerical experiment
  • Bifurcation ; Braided channel ; Channel geometry ; Discharge ; Fluvial dynamics ; Model ; Numerical model ; Sensitivity analysis ; Slope gradient ; Stream
  • This paper presents results of a numerical sensitivity experiment undertaken using computational fluid dynamics (CFD) with the purpose of understanding the flow dynamics of a series of idealized bifurcations. A geometric sensitivity analysis
  • is undertaken for a range of channel slopes (0.005 to 0.03), bifurcation angles (22° to 42°) and a restricted set of inflow conditions based upon simulating flow through meander bends with different curvature on the flow field dynamics through the bifurcation
  • . The results demonstrate that the overall slope of the bifurcation affects the velocity of flow through the bifurcation and when slope asymmetry is introduced, the flow structures in the bifurcation are modified.
  • 2011
  • , local slope, and altitude were measured at 23 channel heads. Hydrological observation revealed stable stream runoff, indicating predominance of groundwater flow. Geomorphic investigation showed a scattered area-slope relationship at channel heads
  • . These results correspond with the previous findings that channel initiation is not controlled by area-slope thresholds in the areas where contribution of groundwater flow to stream runoff is greater.
  • 2011
  • Canada ; Carrying capacity ; Experimentation ; Fluvial dynamics ; Quebec ; Sediment load ; Sediment transport ; Stream ; Stream flow ; Turbulence
  • This study investigates the association between mean and turbulent flow variables and the movement of individual particles in a gravel-bed river. The experimental design implemented in the Eaton-North River (Québec, Canada) is based
  • on the simultaneous observations at a high temporal resolution of both particle movements as bedload using an underwater video camera and of the streamwise and vertical flow velocity components using a vertical array of three electromagnetic current meters (ECMs
  • ). Mean and turbulent flow properties obtained for periods without sediment transport are compared to those when particles were sliding and rolling. In this study, fluid acceleration seems to play a more important role than Reynolds shear stress or normal
  • 2011
  • Tree establishment on bars in low-order gravel-bed mountain streams
  • Alberta ; Canada ; Flood ; Mountain ; Plant colonization ; Riparian vegetation ; River bed ; Rocky Mountains ; Sedimentation ; Stream ; Tree ; Vegetation
  • This study was conducted in first- to third-order streams of Jumping Pound Creek in the Front Ranges of the Canadian Rocky Mountains, west of Calgary, Alberta, to provide an alternative explanation for patterns of tree recruitment in low order
  • gravel-bed mountain streams that does not conform to the standard lateral accretion model of tree recruitment for larger rivers. It is suggested that vertical accretion results in sediment deposition patterns on bars that are often highly patchy
  • . Consequently, tree species and ages are also heterogeneously distributed. Recruitment is fairly continuous on these bars and is not correlated with high water years, suggesting that even flows close to bankfull levels are capable of transporting fine sediment
  • 2011
  • Channel geometry ; Dam ; Gravel ; Hydraulic works ; Sediment budget ; Sediment transport ; Stream ; United States of America ; Wyoming
  • Calibration of the transport relations was based on bed load transport data collected over a wide range of flows on the Snake River and its 2 major tributaries within the study area in 2006 and 2007. Comparison of actual flows with unregulated flows
  • for the period since 1957 shows that operations of Jackson Lake Dam (JLD) have reduced annual peak flows and increased late summer flows. Painted tracer stones placed at 5 locations during the 2005 spring flood demonstrate that despite the reduction in flood
  • 2011
  • Channel ; Channel geometry ; Drainage network ; Hydrological regime ; Model ; Numerical model ; Slope gradient ; Stability analysis ; Stream flow ; Watershed
  • This analysis derives a stability criterion for long-term equilibrium channel heads. The concept of finite perturbation analysis is presented, during which the surface is subjected to perturbations of a finite amplitude and resulting changes in flow
  • path structure and slope are computed. Based on these quantities the analysis predicts whether the perturbed location is going to erode, be filled in or remain steady. The channel head is defined geometrically as the focus point of converging flow lines
  • at the bottom of hollows. It is demonstrated that stability at the channel head grows out of the competition between the rate of flow path convergence and the degree of profile concavity. Analytical functions are derived to compute channel head-contributing area
  • and -slope, flow path convergence and profile concavity as a function of perturbation depth, distance from the crest and the initial slope.
  • 2011
  • Alps (The) ; Austria ; Carrying capacity ; Europe ; Flood ; Model ; Numerical model ; Roughness ; Sediment load ; Slope gradient ; Stream ; Switzerland ; Torrent
  • -calculations of 6 extreme bedload transporting events with the recently developed numerical bedload transport model SETRAC for steep streams. The simulation results show the importance of considering increased flow resistance for small relative flow depth when
  • The aim of this study is to indirectly investigate the role of increased flow resistance on bedload transport by analysing a number of flood events which occurred in August 2005 in the Alps (Austria, Switzerland). To this end, the AA. performed back
  • 2011
  • Arid area ; Botswana ; Climatic change ; Climatic trend ; Climatic variability ; Ephemeral stream ; Stream ; Water resources
  • and their relation to climatic factors. Streamflow is generally stochastic highlighting the importance of factoring in temporal flow variability in water resources planning. There is no clear evidence that changes in climatic variables are related to streamflow
  • 2011
  • Bibliography ; Fluvial dynamics ; Geophysics ; Grain size distribution ; Model ; Runoff ; Sediment load ; Sediment transport ; Stream
  • Bedload, the transport of sediment remaining in contact with the stream bed, has mainly been studied from the perspective of the correlation between fluid driving forces and the responding sediment flux. Yet grain–grain interactions are important
  • and bedload should also be considered as a granular phenomenon. The AA. review progress made recently in the study of granular flows, especially on segregation and rheology, that better illuminates the nature of bedload. Mutual study of these phenomena may
  • 2011
  • Interactions between river flows and colonizing vegetation on a braided river: exploring spatial and temporal dynamics in riparian vegetation cover using satellite data
  • ASTER ; Braided channel ; Data processing ; Flood ; Friuli-Venezia Giulia ; Italy ; LiDAR ; Remote sensing ; Riparian vegetation ; Satellite imagery ; Stream ; Vegetation dynamics ; Vegetation index ; Water regime
  • River, Italy. The study period (2004-2009) of increasing flow disturbance allows the exploration of vegetation dynamics within the river's active corridor under changing flow conditions. The analysis demonstrates the utility of ASTER data
  • 2011
  • China ; Delta ; Digital elevation model ; Earth surface processes ; Holocene ; River mouth ; Sediment transport ; Stream ; Suspended load ; Yangtze
  • This paper examines the morphological development of the Yangtze River mouth, which has been diverting southeasterly (dextrally), according to historical (150 years) chart-based digital evolution model and on-site measured tidal flow data. The AA
  • . reveal a significantly narrowing of the northern river mouth branch due to rapid siltation. Their data have further demonstrated that the ebb flow that dominates in the study area changes its direction gradually from east to southeast. The AA. examine
  • whether the Coriolis Force could explain the dextral diversion of the ebb flow and the altered morphodynamical processes. The Coriolis Force causes an offset in propagation of in-out flow directions at the river mouth area to form a slack water setting
  • 2011