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[1] River confluences are complex hydrodynamic environments where convergence of incoming flows produces complicated patterns of fluid motion, including the development of large-scale turbulence structures. Accurately simulating confluence hydrodynamics represents a considerable challenge for numerical modeling of river flows. This study uses an eddy-resolving numerical model to simulate the mean flow and large-scale turbulence structure at an asymmetrical river confluence with a concordant bed when the momentum ratio between the two incoming streams is close to 1. Results of the simulation are compared with field data on mean flow and turbulence structure. The simulation shows that the mixing interface is populated by quasi-two-dimensional eddies. Successive eddies have opposing senses of rotation. The mixing layer structure resembles that of a wake behind a bluff body (wake mode). Strong streamwise-oriented vortical (SOV) cells form on both sides of the mixing layer, a finding consistent with patterns inferred from the field data. The predicted mean flow fields show that flow curvature has an important influence on streamwise variation of circulation within the cores of the two primary SOV cells. These SOV cells, along with vortices generated by flow over a submerged block of sediment at one of the banks, strongly influence distributions of the streamwise velocity and turbulent kinetic energy downstream of the junction. Comparison of the eddy-resolving simulation results with predictions from the steady Spalart-Allmaras RANS model shows that the latter fails to predict important features of the measured distributions of streamwise velocity and turbulent kinetic energy because the RANS model underpredicts the strength of the SOV cells. Analysis of instantaneous and mean bed shear stress distributions indicates that the SOV cells enhance bed shear stresses to a greater degree than the quasi-two-dimensional eddies in the mixing interface.

A recent opinion piece rekindled debate as to whether geography's current interdisciplinary make-up is a historical relic or an actual and potential source of intellectual vitality. Taking the latter position, we argue here for the benefits of sustained integration of physical and critical human geography. For reasons both political and pragmatic, we term this area of intermingled research and practice critical physical geography (CPG). CPG combines critical attention to power relations with deep knowledge of biophysical science or technology in the service of social and environmental transformation. We argue that whether practiced by individuals or teams, CPG research can improve the intellectual quality and expand the political relevance of both physical and critical human geography because it is increasingly impractical to separate analysis of natural and social systems: socio-biophysical landscapes are as much the product of unequal power relations, histories of colonialism, and racial and gender disparities as they are of hydrology, ecology, and climate change. Here, we review existing CPG work; discuss the primary benefits of critically engaged integrative research, teaching, and practice; and offer our collective thoughts on how to make CPG work.Keywords: physical geography, critical human geography, transdisciplinarity, anthropoceneIntervention en géographie physique critique Un article d'opinion paru récemment est à l'origine de la relance d'un débat qui pose la question à savoir si le fondement interdisciplinaire actuel de la géographie serait une relique historique ou une source réelle et potentielle de vitalité intellectuelle. En prenant la défense de la seconde position, nous militons en faveur des bénéfices découlant de l'intégration soutenue de la géographie physique et de la géographie humaine critique. Pour des raisons à la fois politiques et pragmatiques, nous avons nommé ce domaine de recherche et de pratique enchevêtré la géographie physique critique (GPC). C'est au service de la transformation sociale et environnementale que la GPC intègre un regard critique sur les relations de pouvoir à la connaissance profonde de la science ou de la technologie biophysique. Que se soient des individus ou des équipes qui la pratiquent, les travaux de recherche en GPC peuvent contribuer à l'amélioration de la qualité intellectuelle et à l'élargissement de la pertinence politique de la géographie humaine critique et géographie physique, compte tenu que la séparation de l'analyse des systèmes naturels et des systèmes sociaux pose des difficultés d'ordre pratique. À l'origine des paysages sociobiophysiques se trouvent autant les relations inégales de pouvoir, les histoires de colonialisme et les disparités raciales et entre les sexes que l'hydrologie, l'écologie et les changements climatiques. Dans cette partie de l'article, nous passons en revue les travaux actuels en GPC, nous engageons une discussion sur les principaux avantages des approches intégratives et véritablement critiques en recherche, dans l'ense...

The planform dynamics of meandering rivers produce a complex array of meander forms, including elongated meander loops. Thus far, few studies have examined in detail the flow structure within meander loops and the relation of flow structure to patterns of planform change. This field-based investigation examines relations between three-dimensional fluid motion and channel change within an elongated, asymmetrical meander loop containing multiple pool-riffle structures. The downstream velocity field is characterized by a high-velocity core that shifts slightly outward as flow moves through individual lobes of the loop. For some of the measured flows this core becomes submerged below the water surface downstream of the lobe apexes. Vectors of cross-stream/vertical velocities indicate that skew-induced helical motion develops within the pools near lobe apexes and decays over riffles where channel curvature is less pronounced. Maximum rates of bank retreat generally occur near lobe apexes where impingement of the flow on the outer channel bank is greatest. However, maximum rates and loci of bank retreat differ for upstream and downstream lobes of the loop, leading to increasing asymmetry of loop geometry over time -a finding consistent with experimental investigations of loop evolution.