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Nancy Martel

 

Étudiante 2è cycle

Department of biology, chemistry and geography, UQAR

Des Ursulines Building
300 Allée des Ursulines
UQAR
Quebec, Canada
G5L 3A1

418.723.1986 extension 1733
Nancy.Martel@uqar.ca

 

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Direction

 
 

Research project

Studies on river confluences have highlighted the complex relationships between flow structure, sediment transport and bedforms development. The flow structure at river confluences is influenced by the junction angle, by the momentum flux ratio and by the bed morphology. Although the flow structure at river confluence is relatively well documented and the general effect of an ice cover on the flow is known, the relationship between the flow structure and the presence of an ice cover at a confluence has yet to be explored. The aim of this study is to characterize and compare the flow structure at a medium sized confluence with and without an ice cover. The confluence of the Mitis-Neigette River is located in Sainte-Angèle-de-Mérici in Eastern Québec. The difference in turbidity between the two rivers allows the position of the shear layer and turbulent structures to be observed when the flow is without ice. The confluence was selected because a thick ice cover is present for most of the winter allowing for safe field work.The project relies on two field campaigns. A winter field campaign where ice-cover measurements were taken in addition to hydraulic and morphological measurements and a summer campaign to acquire similar measurements in the absence of an ice cover. For both campaigns, velocity profiles are collected with an acoustic Doppler current profiler (ADCP) to reconstruct the three-dimensional flow structure from several velocity profiles. Vertical profiles are also measured using an acoustic Doppler velocimeter (ADV) to characterize the size and frequency of turbulent flow structures within the shear layer. The project presents many challenges in both logistics and data analysis. In the winter, measuring velocity profiles in the field is complicated because of the cold affecting the instrumentation and field assistants. Also, the location of the shear layer was difficult to evaluate in winter conditions. In the summer, high flow velocities and the deep scour hole challenge the use of instrumentation attached along a pole because of problems of vibration. Despite these challenges, the results of this project allow one of first documentations of the flow structure at a river confluence with ice cover.

 
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