Author(s): Wim S.J. Uijttewaal
Keywords: Coherent structures; mixing; rivers; roughness; shallow flows; turbulence
Abstract: Shallowness defines a wide class of flows of high significance to hydraulic and environmental engineering. This paper discusses research on shallow flows that have been carried out in laboratory and field studies as well as with numerical simulations. Recent advances in experimental and numerical techniques helped to reveal the important features of shallow flows which are directly relevant to rivers. Particular attention is paid to the contribution of large-scale structures to transverse transport of momentum and mass which is assessed for archetypical flow configurations like wakes, shear layers, and bend flows. It is demonstrated that the flow geometry and roughness distribution determine the relative contribution of secondary circulation and large-scale turbulent structures to this transport. For applications in civil and environmental engineering, a proper parameterization of the physical processes is required for representing shallow flows at the large scale. The paper outlines some perspective directions to be developed in the forthcoming years.