inscription
PORTAIL D'INFORMATION GÉOGRAPHIQUE

Résultats de la recherche (4459 résultats)

Affinez votre recherche

Par Collection Par Auteur Par Date Par Sujet Par Titre
  • Failure and flow on a 35o slope : causes and three-dimensional observations
  • Three-dimensional characteristics of the active debris flow are reconstructed from mudlines on 58 trees still standing in the flow path. Mudline formation only on the up-flow side of trees indicates relatively high viscosity of the debris flow
  • . Mudline height is a function of the maximum thickness and velocity of the flow at any tree.
  • Probing a traffic congestion controversy : density and flow scrutinized
  • Congestion ; Flow ; Optimization ; Road ; Spatial equilibrium ; Traffic ; Transport
  • Optimization requires equilibrium flow to decrease under mild congestion, but increase under hypercongestion. However, both increasing flow needed under hypercongestion and decreasing flow needed under mild congestion should be accompanied
  • by decreasing density. Thus, inflow of vehicles should always be discouraged to either increase or decrease flow of vehicles for economic efficiency. Moreover, even when optimal policy requires equilibrium flow to increase, the optimal flow itself must decrease
  • Overland flow and soil erosion : some processes and their interactions
  • Carrying capacity ; Flow ; Model ; Overland flow ; Sediment transport ; Soil erosion
  • Flow detachment, sediment transport and interactions between flow characteristics and sediment load are discussed here. Descriptions of the interactions between sediment load and flow characteristics, namely mean flow velocity, obtained through
  • Effect of saltating sediment on flow resistance and bred roughness in overland flow
  • This study has evaluated the effect of saltating sediment on flow resistance and bed roughness in overland flow on a fixed sand-covered bed. It is concluded that saltating sediment has a considerable impact on overland flow hydraulics, at least
  • on fixed granular beds. Saltation is likely to have a relatively smaller effect on overland flow on natural hillslopes and agricultural fields where form and wave resistance dominate.
  • A comparison of flow intensities in alluvial rivers : characteristics and implications for modelling flow processes
  • Forecast ; Least squares method ; Linear regression ; Methodology ; Model ; Stream ; Stream flow ; Turbulence
  • This paper compares flow intensity data obtained with different instruments from a variety of fluvial environments. It examines associations between the root-mean-square of longitudinal velocity fluctuations (flow intensity), local mean velocity
  • , relative depth, and boundary resistance. Preliminary approaches to prediction and modelling of variations in flow intensity are suggested based upon linear regression relationships.
  • Violence in pyroclastic flow eruptions in Tephra studies.
  • Violence reflects the vigour with which a pyroclastic flow is emplaced. It is described quantitatively by the height of hills climbed by the flow (yielding flow-velocity estimates), the overall morphology of the deposit and by the proportion
  • of the flow which forms an ignimbrite veneer deposit. Using the Taupo ignimbrite (New Zealand) as an example of an extremely violent flow, we relate violence to the eruption intensity. The AA. consider that eruption magnitude and intensity control the gross
  • distribution of a pyroclastic flow deposit.
  • Visualization of the turbulent flow structure in a gravel-bed river
  • Canada ; Hydrodynamics ; Model ; Programming ; Rocky Mountains ; Stream ; Stream flow ; Turbulence
  • A novel technique for visualizing turbulent flow data from a gravel-bed river is presented. The time development of flow velocity and shear stress at three heights is displayed using a computer program. This can be used to observe how
  • the fluctuations of velocity and shear stress interact both spatially and temporally. The AA. highlight examples of flow events which are important for the understanding of flow dynamics.
  • Macroscale surface roughness and frictional resistance in overland flow
  • Hydrology ; Inundation ; Microrelief ; Model ; Overland flow ; Roughness ; Runoff ; Watershed
  • The aim of this paper is to pose a broad model for the hydraulics of overland flow by assessing the dependence of the friction factor on an inundation ratio at 3 stages of progressive flow inundation. The development of the model is prefaced
  • by a brief review of the physical variables which may contribute to flow resistance and some of the possible dimensionless groupings arising from those variables. Previously published field and laboratory data are re-evaluated in terms of the frictional
  • resistance as a function of an estimated inundation ratio for each flow, and the results are compared with the trends predicted by the model.
  • Morphology of the 1984 open-channel lava flow at Krafla volcano, northern Iceland
  • Aerial photography ; Caldera ; Cartography ; Fault ; Iceland ; Lava flow ; Model ; Rock mechanics ; Volcanic eruption ; Volcanism
  • This paper presents results of a detailed mapping and field study of the 1984 open-channel lava flow. Identified surface-texture types are described as flow facies. Lava flow dimensions are assessed by combining the pre- and post-flow topography
  • to get a realistic figure of the dimensions of the lava flow. Video recordings are also used to draw conclusions about the development of the flow during eruption. Lava flow models are then discussed in the light of topographic data and observations.
  • Effects of flow regulation on flow regime in the Murrumbidgee River, South Eastern Australia : an assessment using a daily estimation hydrological model
  • Australia ; Flood ; Hydraulic works ; Hydrological regime ; Model ; New South Wales ; Stream ; Stream flow ; Water management
  • In this paper, modelled hydrological data are used to quantify the effects of regulation on the flow regime of the lower Murrumbidges River in the period 1970-1988. The comparison of modelled natural and regulated daily flows shows the magnitude
  • of changes to mean and seasonal flows, flood peaks and flow duration. The AA. compared historical regulated data with modelled natural data over a common 29 year period to eliminate the effect of secular climate change on flow data and the daily time-step
  • The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers : a reply
  • Carrying capacity ; Flood ; Flow ; Fluvial hydrology ; Fluvial processes ; River bed ; Sediment transport ; Turbulence
  • The inference that flow and form are dynamically linked is in sympathy with the own conclusions of the AA. that cluster spacing is an equilibrium condition governed by the interplay of flow resistance and sediment transport.
  • Hydraulic geometry and changes in flow velocity at a river confluence with coarse bed material
  • The purpose of this paper is to report observations of flow processes occuring at a natural stream confluence and to illustrate the interactions between form and flow as water stage is varied. Changes in flow velocity at the confluence will also
  • Critical flow in rockbed streams with estimated values for Manning's n - Comment and reply
  • Hydrodynamics ; Slope gradient ; Stream ; Stream flow
  • H. Chanson comments some aspects of the Tinkler's paper (1997) regarding critical flow, critical slope calculations and boundary shear stress distributions in undular flows, and K.J. Tinkler replies in turn.
  • Resistance to flow past deformable boundaries
  • An hypothesis from which a general principle covering deformation of alluvial boundaries may be developed is proposed, namely flow of fluid past a deformable boundary will deform the boundary so as to increase the resistance to flow. Upon attainment
  • of a local maximum of resistance to flow the boundary shape will cease to change.
  • Volumetric displacement of flow depth by obstacles, and the determination of friction factors in shallow overland flows
  • Applied hydrology ; Discharge ; Experimentation ; Overland flow ; Rill wash ; Roughness ; Runoff ; Soil erosion ; Water erosion
  • Large roughness elements such as stones or plant stems (obstacles) influence the depth of overland flows in 2 ways. The first effect is a dynamic one, involving frictional retardation of the flow and associated reduction in flow speeds. The second
  • influence is static, and arises from the upward volumetric displacement of flow depth because of the submerged volume of the obstacles.To understand the true frictional drag arising from obstacles , a correction must be made for the volumetric displacement
  • Flow threads in surface run-off : implications for the assessment of flow properties and friction coefficients in soil erosion and hydraulics investigations
  • Arid area ; Australia ; Experiment plot ; Microrelief ; New South Wales ; Overland flow ; Runoff ; Soil erosion ; Water erosion
  • New field experiments were made on untilled soil surfaces in arid western New South Wales, Australia, to explore the implications for deriving meaningful measures of flow properties, including friction coefficients. A new approach to the evaluation
  • of friction coefficients in non-uniform flows is advanced, involving the determination of separate coefficients for threads and non-thread zones of the flow field. In contrast, flow-field friction coefficients as they are customarily derived in run-off plot
  • Modelling floodplain flows using a two-dimensional finite element model
  • Devon ; Earth surface processes ; England ; Floodplain ; Flow ; Fluvial hydrology ; Fluvial processes ; Model ; United Kingdom
  • A prototype two-dimensional finite element flow model for depth-averaged free surface flows is developed for floodplain environments. Preliminary model results indicate that this modelling approach can be used to identify dynamic variations
  • in the flow field parameters over length scales of the order of 10-100 m. Potentially, such data have the ability to permit detailed analysis of short-term floodplain sedimentary dynamics.
  • Variations in the association between mid-tropospheric flow and surface temperatures across the United States
  • Variations in the association between mid-tropospheric flow and mid-latitude surface temperatures are examined by correlating multiple indices of a surrogate measure of mean monthly 500-mb flow with mean monthly surface temperatures across
  • the conterminous United States from 1951-80. There are major changes in the key areas of flow from one season to the next. Temperatures in the northwest and southeast appear to be most strongly associated with flow conditions.
  • Water movement in a structured soil in the south-east of Ireland : preliminary evidence for preferential flow
  • A study was carried out on a structured soil in the south-east of Ireland to investigate flow patterns of water in soil. The results provided preliminary evidence for preferential flow in the soil. Nitrate leaching data, from a grazing study, tended
  • to confirm the results. The importance of preferential flow with regard to movement of manures and chemicals towards groundwater, which will depend on the timing of the application of those substances and the occurrence of significant rainfall events
  • is discussed. Soils having physical characteristics conducive to preferential flow are illustrated.
  • Inception of sediment transport in shallow overland flow
  • Model ; Overland flow ; Rill wash;Runoff ; Sediment transport ; Soil erosion
  • Literature suggests that the Shields criterion is not well suited to predicting the inception of sediment transport in overland flow. A new approach to transport inception in overland flow is proposed, which avoids measurement difficulties
  • and friction law uncertainties. A preliminary model, valid for uniform flow over non-cohesive material, is developed.