Exploring turbulence-sediment dynamics for river erosion control

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The applicant proposes to study turbulence and its interaction with sediments in water channels. Turbulence over channel-beds causes bed-sediment scour and deposition, influencing the stability of a river channel. Channel instability has a detrimental impact on the effectiveness of river engineering schemes for flood control, navigation improvement, and the safe use of in-stream structures. The flow dynamics of the sediment-water interface region are complex and poorly understood. The objective of the proposed research is to provide an improved understanding of complex flow dynamics. In a river confluence, two streams of different flow velocities combine to form a single channel, the combining flow features velocity shear. The associated vorticity can lead to hydrodynamic instability and the development of turbulence. Turbulent eddies have the ability to scour sediment particles from the bed and sweep them downstream. Past research has focused on turbulent mixing between the incoming fluids, assuming negligible bed friction. This assumption is invalid for flows through a shallow confluence. The applicant intends to investigate the role of shallowness in the interaction between fluid- and sediment-particles by means of laboratory measurements and particle trajectory simulations. The simulations will consider both open-water and ice-covered conditions. The results will be useful for the development of effective strategies for the protection of confluence stability and benthic ecology. In a channel expansion, water flow typically separates from one or both of its sidewalls. Flow separation creates turbulent eddies of various sizes. Larger eddies bear more energy and are capable of interacting with sediment particles. The result is scour, deposition, and bed evolution within the expansion and often further downstream. The applicant plans to conduct laboratory experiments and morphodynamic simulations in order to find solutions to the problem of scour in channel expansions. The applicant will use advanced measurement techniques (laser Doppler anemometry and three-dimensional particle tracking velocimetry) to produce reliable measurements of the instantaneous flow velocity and particle trajectories. Digital positioning devices will allow accurate and repeatable measurements. The applicant will perform particle tracking simulations and high-resolution sediment scour simulations on high performance computing clusters. The laboratory measurements and the mathematical predictions are complementary to each other. In Canada, turbulence-induced erosion is omnipresent in rivers, streams, drainage canals, and water supply channels. The results from this proposed research will help achieve two long-term objectives: (a) developing sound analysis and prediction strategies to support practical and managerial activities in river engineering and water resources engineering; (b) creating reliable data for decision makers to address environmental and economic needs.