River confluences are characterized by a complex mixing zone with three‐dimensional (3D) turbulent structures which have been described as both streamwise‐oriented structures and Kelvin–Helmholtz (KH) vertical‐oriented structures. The latter are visible where there is a turbidity difference between the two tributaries, whereas the former are usually derived from mean velocity measurements or numerical simulations. Few field studies recorded turbulent velocity fluctuations at high frequency to investigate these structures, particularly at medium‐sized confluences where logistical constraints make it difficult to use devices such as acoustic doppler velocimeter (ADV). This study uses the ice cover present at the confluence of the Mitis and Neigette Rivers in Quebec (Canada) to obtain long‐duration, fixed measurements along the mixing zone. The confluence is also characterized by a marked turbidity difference which allows to investigate the mixing zone dynamics from drone imagery during ice‐free conditions. The aim of the study is to characterize and compare the flow structure in the mixing zone at a medium‐sized (~40 m) river confluence with and without an ice cover. Detailed 3D turbulent velocity measurements were taken under the ice along the mixing plane with an ADV through eight holes at around 20 positions on the vertical. For ice‐free conditions, drone imagery results indicate that large (KH) coherent structures are present, occupying up to 50% of the width of the parent channel. During winter, the ice cover affects velocity profiles by moving the highest velocities towards the centre of the profiles. Large turbulent structures are visible in both the streamwise and lateral velocity components. The strong correlation between these velocity components indicates that KH vortices are the dominating coherent structures in the mixing zone. A spatio‐temporal conceptual model is presented to illustrate the main differences on the 3D flow structure at the river confluence with and without the ice cover. © 2019 John Wiley & Sons, Ltd.

River confluences are characterized by a complex mixing zone with three-dimensional turbulent structures, which can be affected by the presence of an ice cover during the winter. The objective of this study is to characterize the flow structure in the mixing zone at a medium-size (~ 40 m) river confluence with and without an ice cover. Detailed velocity profiles were collected under the ice along the mixing plane with an Acoustic Doppler Velocimeter. For the ice-free conditions, drone imagery was used to characterize the mixing layer structures for various flow stages. Results indicate that during the ice-free conditions, very large Kelvin-Helmholtz (KH) coherent structures are visible due to turbidity differences, and occupy up to 50% of the width of the parent channel. During winter, the ice cover affects velocity profiles by moving the highest velocities towards the center of the profiles. Large turbulent structures are visible in both the streamwise and lateral velocity components. The strong correlation between these velocity components indicates that KH vortices are the dominating coherent structures in the mixing zone. A spatio-temporal conceptual model is presented to illustrate the main differences on the three-dimensional flow structure at the river confluence with and without the ice cover.

Les mutations de l’organisation du travail remettent en question le cadre traditionnel d’exécution du travail et transforment la disponibilité temporelle attendue du salarié, qui s’étend bien au-delà de la période pendant laquelle il exécute un travail. Cette obligation du salarié d’être disponible pour répondre à une éventuelle demande de l’employeur a pour conséquence d’étendre les risques reliés au travail au-delà des lieux de l’entreprise ou du temps spécifiquement consacré à l’exécution du travail. Notre article a pour objectif de déterminer, au moyen d’une analyse jurisprudentielle, si l’expression « à l’occasion du travail », comprise dans la définition de la notion d’« accident du travail » dans la Loi sur les accidents du travail et les maladies professionnelles, permet de reconnaître les lésions subies par des travailleurs qui sont assujettis à une obligation de disponibilité. Globalement, l’application ou l’interprétation des termes « à l’occasion du travail » paraît favorable à la reconnaissance des lésions subies par des travailleurs soumis à une telle obligation. Toutefois, une analyse du contenu des décisions révèle que l’interprétation de cette expression n’est pas uniforme. D’une part, il existe deux courants d’interprétation de celle-ci dans la jurisprudence étudiée, courants qui ne reconnaissent pas de manière équivalente le caractère professionnel des lésions subies par des travailleurs assujettis à des obligations de disponibilité similaires. D’autre part, l’organisme administratif chargé de statuer sur des réclamations de travailleurs assujettis à une obligation de disponibilité paraît peu enclin à conclure qu’il s’agit de lésions professionnelles, contrairement aux décisions rendues par le tribunal.