Suomen vesistojen bifurkaatiot. (The bifurcations of Finnish watercourses)
Bifurcation ; Cours d'eau ; Finlande ; Géographie de l'Europe ; Réseau de drainage
About 40 lake and 25 river bifurcations in Finland are described in this article. According to their location, the bifurcations can be classified to external and internal bifurcations. An external bifurcation is located on the divide, either between
two river basins or between two subbasins. An internal bifurcation occurs within a river basin or subbasin. The branches of an internal bifurcation have a junction downstream| if at least one branch has a tributary before the junction, the bifurcation
is an ordinary internal bifurcation. If the discharge in both branches remains unchanged, the branching is called pseudobifurcation. Some of the bifurcations are temporary| 14 lake and 16 river bifurcations can be considered perennial. Some of lake bifurcations
Stability, morphology and surface grain size patterns of channel bifurcation in gravel-cobble bedded anabranching rivers
Bifurcation ; Canada ; Chenal anastomosé ; Cours d'eau ; Granulométrie ; Géométrie hydraulique ; Méandre ; New Brunswick
Bifurcation ; Braided channel ; Canada ; Channel geometry ; Grain size distribution ; Meander ; New Brunswick ; Stream
This study presents a detailed field study of the morphology and bed sediment patterns of 5 channel bifurcations on the Renous River, New Brunswick, and a regional description of bifurcation angles within anabranching rivers in the Miramichi Basin
, New Brunswick. The stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term.
Bifurcation ; Diffusion ; Dynamique de système ; Economie spatiale ; Equilibre spatial ; Généralités sur la géographie ; Localisation industrielle ; Simulation
Exemple et débat sur les causes multiples de bifurcation dans les phénomènes spatiaux. Interprétation d'un modèle en termes d'économie spatiale (concentration-diffusion-équilibre).
Multiple bifurcation effects with a logistic attractiveness function in the supply side of a service system
Attraction commerciale ; Bifurcation multiple ; Commerce de détail ; Généralités sur la géographie ; Localisation ; Modèle urbain ; Théorie des catastrophes
Effets de bifurcation multiple quand la fonction d'attraction commerciale, de type Lakshmanan-Hansen, est remplacée par une fonction logistique. Richesse des structures spatiales dérivées de la localisation des commerces de détail.
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.
La composante géographique dans une bifurcation systémique : le cas de l'Europe de l'Est
Bifurcation ; Découpage administratif ; Espace économique ; Etat ; Europe ; Europe de l'Est ; Géographie politique ; Géopolitique ; Restructuration économique ; Régime politique ; Système spatial
Administrative division ; Bifurcation ; Eastern Europe ; Economic restructuring ; Economic space ; Europe ; Geopolitics ; Government ; Political geography ; Spatial system ; State
Après la bifurcation macrogéopolitique de 1989, sommes-nous capables de distinguer certains de ses composants démocratiques locaux ou régionaux? Le délai de réponse, notion fondamentale pour la mise en route de nouvelles interactions spatiales
multiples, sera déterminant dans ce processus de transition-bifurcation.―(RS)
Les bifurcations de la politique énergétique française depuis la guerre
Le paradoxe de la politique énergétique française depuis trente ans, c'est qu'à chacune de ses bifurcations les productivistes l'ont régulièrement emporté sur les autonomistes, à qui l'Histoire semble pourtant toujours finir par donner raison.
River bifurcations are critical but poorly understood elements of many geomorphological systems. They are integral elements of alluvial fans, braided rivers, fluvial lowland plains, and deltas and control the partitioning of water and sediment
through these systems. This review synthesizes our current understanding of bifurcations and brings together insights from different research communities and different environmental settings. The AA. consider the causes and initiation of bifurcations
and avulsion, the physical mechanisms controlling bifurcation and avulsion evolution, mathematical and numerical modelling of these processes, and the possibility of stable bifurcations. They end the review with some open questions.
Effects of helical flow in one-dimensional modelling of sediment distribution at river bifurcations
Bifurcation ; Cours d'eau ; Hydrogéomorphologie ; Lit fluvial ; Modèle ; Pays-Bas ; Rhin ; Transport sédimentaire
Bifurcation ; Hydrogeomorphology ; Model ; Netherlands (The) ; Rhine ; River bed ; Sediment transport ; Stream
Complex flow processes at river bifurcations and the influence of the layout of a bifurcation make it difficult to predict sediment distribution over the downstream branches in case bedload transport dominates. In one-dimensional models a nodal
point relationship, that prescribes the distribution of sediment over the downstream branches, is needed. The AA. have identified which factors need to be included in such a relationship for the division of bedload transport at bifurcations
. The relationship has been tested against data from a unique set of laboratory measurements, numerical data and data from a scale model of the Rhine bifurcation at Pannerden in the Netherlands. It is concluded that deriving a practical physics-based 1-D relationship
including all relevant processes is not feasible. The AA. therefore recommend 2-D or 3-D modelling for all cases in general where morphological evolution depends on the division of bedload transport at bifurcations.
Bifurcation ; Channel geometry ; Delta ; Earth surface processes ; Meander ; Model ; Netherlands (The) ; Rhine ; River bed ; Stream
The aim of this paper is to identify and quantify factors that determine avulsion duration in meandering lowland rivers, and to assess the sedimentary styles associated with bifurcation evolution. The AA. formulate a morphodynamic model and compare
results of scenario modelling to the historic apex bifurcation of the river Rhine of the last 2000 years. The model incorporates channel width adjustment and some effects of meandering on the flow and sediment partitioning at the bifurcation. Rich
historical resources and geological data are available, allowing to infer the possible effects of meandering at the bifurcation, changing channel widths, vegetation in the abandoning channel and sedimentation independently from the model. Furthermore the AA
. reconstruct the sedimentary styles associated with the bifurcation from a geological cross-section, in particular channel migration, channel widening and narrowing and channel belt formation up to the residual channel stage.
The aim of this paper is to explore the interaction between bedform steered flow and bifurcation dynamics. The AA. present the predicted flow dynamics from the application of a Reynolds-averaged Navier–Stokes (RANS) model to a series of bifurcation
geometries with morphologies measured during previous flume experiments. The topography of the bifurcations consists of either plane or bedform-dominated beds which may or may not possess discordance between the 2 bifurcation distributaries. The results
demonstrate the dominant effect bed discordance has upon flow division between the 2 distributaries. They also suggest that sand-bed river bifurcations are more likely to have an influence that extends much further upstream and have a greater impact upon water
Aspects of catastrophe theory and bifurcation theory in regional science in Nineteenth European Congress, London, 1979.
Analyse de système ; Bifurcation ; Généralités sur la géographie ; Mathématique ; Science régionale ; Stabilité structurale ; Système ; Théorie ; Théorie des catastrophes ; Trajectoire
Présentation des formes générales mathématiques des systèmes dynamiques et des conditions de changement de comportement de ces systèmes (bifurcation): interdépendance des variables et non-linéarité. Idées d'application en science régionale, l'A
Bar ; Bifurcation ; Braided channel ; Channel geometry ; Flood ; Italy ; Northeast Italy ; Space time ; Stream
Field data are presented here on a bifurcation in the Tagliamento River, northeast Italy. The planform configuration of the bifurcation and its temporal evolution was monitored by an automatic digital camera during a series of 7 floods
with different magnitudes. Digitized maps of the channels provided information on the location of the bifurcation, the width of the anabranches, the angle between them, along with the occurrence and migration of sediment bars. Data were acquired at 2 different
water levels. A relationship between width asymmetry and flood magnitude was observed. Moreover, the analysis based on recent theoretical findings pointed out the relevance of a correct assessment of the characteristic temporal scales, as the bifurcation
The problem of the bifurcated flow of the Vistula River of Fordon (Bydgoszcz) against the background of the evolution of the Toruń basin at the end of the Plenivistulian
-textural research of the deposits forming the terraces near Bydgoszcz and those near the Vistula River gap of Fordon, reference was made to the problem of the genesis of this river gap. The results of the research suggest that the bifurcation phase
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
Bifurcation ; Dynamique de système ; Fonction d'utilité ; Modèle urbain ; Optimisation ; Population urbaine ; Structure urbaine ; Système ; Système spatial
Bifurcation ; Optimization ; Spatial system ; System ; System dynamics ; Urban model ; Urban population ; Urban structure ; Utility function
modélisation dynamique non linéaire est effectuée, qui décrit l'état du système spatial ouvert, avec intervention éventuelle, de phénomènes d'auto-organisation et de bifurcation.