Turbulent flow structures in alluvial channels with curved cross-sections under conditions of downward seepage

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Experimental investigations have been done to analyze turbulent structures in curved sand bed channels with and without seepage. Measures of turbulent statistics such as time-averaged near-bed velocities, Reynolds stresses, thickness of roughness sublayer and shear velocities were found to increase with application of downward seepage. Turbulent kinetic energy and Reynolds normal stresses are increased in the streamwise direction under the action of downward seepage, causing bed particles to move rapidly. Analysis of bursting events shows that the relative contributions of all events (ejections, sweeps and interactions) increase throughout the boundary layer, and the thickness of the zone of dominance of sweep events, which are responsible for the bed material movement, increases in the case of downward seepage. The increased sediment transport rate due to downward seepage deforms the cross-sectional geometry of the channel made of erodible boundaries, which is caused by an increase in flow turbulence and an associated decrease in turbulent kinetic energy dissipation and turbulent diffusion.

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