Flow processes and river dynamics

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Alluvial rivers are complex and fundamental components of the natural environment and a key resource for human activities and for wildlife. Although river systems have been extensively studied in the past, their dynamics and response to environmental changes, both natural and anthropogenic, are still far from being understood. Numerous spectacular examples of major and unforeseen impacts on the shape, size and pattern of alluvial channels have been caused by severe floods or by periods of drought such as those recently witnessed in Europe, North America, and elsewhere. In order to understand the behaviour of rivers we need to advance our knowledge on the fundamental mechanical processes that drive the river system. This research program focuses on the relationships, feedbacks and mutual adjustments between flow structure, sediment mobility and the resulting adjustments of the bed (form and bed material distribution) in rivers. The particular scope of the research is on the role of flow turbulence (i.e. smaller scales of motion in fluid flow) in these relationships. The objectives of the research program are to: develop a better model of the properties, origin and evolution of large-scale turbulent flow structures in uniform and non-uniform river flows; to quantify and understand changes in flow structures as flow stage changes; to integrate turbulence in the characterisation of the variability of patches and to assess the role of turbulence on fish behaviour; quantify the relations between flow structures and bedload sediment transport; determine the effects of bed morphology on bed particle movements at the reach scale. These objectives will be met through interconnected projects that will rely on both classical and innovative methods and experimental designs. The experiments will be conducted in rivers in eastern Québec at a selection of field sites, some of which have permanent installations for the measurements of flow, bed topography and particle displacements. The results of this research will be used to improve current models on the development of turbulence and on the effects of turbulence on fish behaviour and sediment transport.