Confluence | EPFL Graph Search

In geography, a confluence (also: conflux) occurs where two or more flowing bodies of water join to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); or where two streams meet to become the source of a river of a new name (such as the confluence of the Monongahela and Allegheny rivers at Pittsburgh, forming the Ohio); or where two separated channels of a river (forming a river island) rejoin at the downstream end. Scientific study of confluences Confluences are studied in a variety of sciences. Hydrology studies the characteristic flow patterns of confluences and how they give rise to patterns of erosion, bars, and scour pools. The water flows and their consequences are often studied with mathematical models. Confluences are relevant to the distribution of living organisms (i.e., ecology) as well; "the general pattern [downstream of confluences] of increasing stream flow and decreasing

Lyon-Confluence. Un nouveau quartier résidentiel pour Perrache (Lyon, F)

Le projet urbain constitutif de ce nouveau quartier résidentiel et tertiaire trouve sa place à l'intérieur de limites bien distinctes qui confèrent aux aménagements la richesse de leurs qualités fonctionnelles spatiales et relationnelles. A l'Est une voie ferrée, surélevée par un viaduc, coupe littéralement la presqu'île de Lyon en deux ensembles déconnectés. La traversée de l'ouvrage permettra une nouvelle lecture transversale de ce morceau de ville. Au Sud, un bassin de plaisance en cours d'élaboration constituera une nouvelle place publique qui permettra au quartier de trouver sa respiration par rapport au pôle de loisirs qui verra le jour dans les prochaines années. Le projet se pose en terme de revitalisation de ce morceau Ouest de la presqu'île, laissé jusqu'alors à une activité industrielle aujourd'hui vouée au déclin. Le plan masse qui détermine la morphologie du quartier exprime la volonté d'ouverture sur les collines de l'Ouest lyonnais, par delà la Saône, qui offre un paysage boisé au regard du nouvel ensemble d'habitations. Les grands équipements publics trouvent quant à eux leur place le long de la voie ferrée. Le projet exprime la diversité des relations à l'espace collectif, qu'il soit privé ou public. Les îlots fermés à cour surélevée composent un système de ramification à partir de la voie ferrée. Ils irriguent un grand espace public paysager dans lequel viennent s'insérer les barres de logements sur pilotis renforçant le caractère fluide de ce grand espace ouvert.

2004

Hydro-morphodynamic differences induced by different angles in an experimental discordant confluence

Sebastián Guillén Ludeña

Confluences, within the fluvial network, are considered particular areas with great ecological value, where flow dynamics and bed morphology are complex and highly three-dimensional. Several parameters influence the morphodynamics and hydrodynamics of river confluences including discharge and momentum ratios, angle of confluence and sediment transport. Confluences with low discharge and momentum ratios, where narrow steep tributaries with high sediment load join a wide low-gradient main-channel that provides the dominant discharge, are often observed in the Upper-Rhone river in Switzerland. Few existing studies have looked at the hydro-morphodynamics of this type of river confluences considering sediment discharge in both confluent channels. This paper aims to analyze the influence of the confluence angle on the flow dynamics and bed morphology of this type of confluences in an experimental facility under movable bed conditions. For that purpose, two experiments were carried out in a laboratory confluence with low discharge and momentum ratios (Qr = 0.11 and Mr = 0.16 respectively), and with two different confluence angles (α = 90° and 70°). During the experiments, two distinct poorly shorted sediment mixtures were supplied into the tributary and into the main channel at constant but different rates for each flume. The experiments were run until equilibrium in bed morphology was reached. During the experiments bed topography surveys were systematically recorded, and water surface was measured at equilibrium. These measures illustrate the bed topography evolution during the experiments, and the confluence hydrodynamics at equilibrium. The results show that different confluence angles resulted in different flow regimes and bed elevations in the tributary. Also, the distinct angle configurations yielded different water surface elevations in the main channel upstream of the confluence.

2015

Hydro-morphodynamics of open-channel confluences with low discharge ratio and dominant tributary sediment supply

Sebastián Guillén Ludeña

River confluences in which the tributary supplies the dominant sediment load, and the flow discharge is abundantly provided by the main river, are typically observed in mountain-river basins. The existent knowledge on the hydrodynamic, morphodynamic and sedimentary processes involved in mountain-river confluences is sparse, since most of the studies on confluence dynamics focus on low land confluences. In this context, the present research study aims to deepen the knowledge on the hydro-morphodynamics and sedimentology of mountain-river confluences inspired in those of the Upper-Rhone river basin. For that purpose twelve laboratory experiments were conducted in two experimental facilities: one located at the Laboratory of Hydraulic Constructions of the École Polytechnique Fédérale de Lausanne (LCH-EPFL), and the other one located at the Instituto Superior Técnico de Lisboa (IST-UL). The experimental setup covered a wide range of configurations including three unit-discharge ratios, two junction angles, two sediment mixtures with different gradation coefficients, and two width ratios. The experiments were performed under movable bed conditions and with continuous sediment supply to both flumes, which represents a novelty in the study of this type of confluence. Systematic surveys of bed topography and water surface were recorded at different instants during the experiments and at equilibrium condition. Additionally and also at equilibrium, point velocities were measured and the spatial and grain size distribution of the bed sediments were analyzed. These measurements allowed the analysis of the influence of the discharge ratio, junction angle, sediment gradation and width ratio on the hydro-morphodynamics of open channel confluences. The bed morphology and hydrodynamics displayed some common features that were influenced by the variation of the tested parameters. The most significant morphological features were a marked discordance between the bed elevations of the tributary and main channel, a steep bed slope in the tributary, a bank-attached bar along the inner bank of the main channel and a scour hole that extended from the tributary mouth flanking the bar. The hydrodynamics were mainly characterized by a double flow deflection to the outer bank of the main channel by the tributary inflow and the bank-attached bar, flow acceleration downstream of the confluence, a shear layer that separated each confluent flows, and eventually supercritical flow regime in the tributary depending on the parameter setup. In summary, this research study presents a broad analysis of the hydrodynamic, morphodynamic and sedimentary processes involved in confluences characterized by low discharge ratios, and where the dominant sediment load is supplied by the tributary. This analysis contributes to widen the existent knowledge on the dynamics of this type of confluence and constitutes a benchmark for further studies, as well as a valuable tool for restoration projects.

EPFL2015

Hydro-morphodynamic differences induced by different angles in an experimental discordant confluence

Sebastián Guillén Ludeña

2015

Hydro-morphodynamics of open-channel confluences with low discharge ratio and dominant tributary sediment supply

Sebastián Guillén Ludeña

EPFL2015