Abstract
Several researchers have studied turbulent structures, such as ejections, sweeps, and outwards and inwards interactions in flumes, where the streamwise velocity dominates over vertical and transversal velocities. However, this research presents an experimental study in which there are ejections associated with the interchange between surface and subsurface water, where the vertical velocity dominates over the streamwise component. The experiment is related to a surface alluvial stream that is polluted with fine sediment, which is percolated into the bed. The subsurface flow is modified by a lower permeability associated with the fine sediment and emerges to the surface current. Quasi-steady ejections are produced that drag fine sediment into the surface flow. Particle image velocimetry (PIV) measured the velocity field before and after the ejection. The velocity data were analyzed by scatter plots, power spectra, and wavelet analysis of turbulent fluctuations, finding changes in the distribution of turbulence interactions with and without the presence of fine deposits. The flow sediment ejection changes the patterns of turbulent structures and the distribution of the turbulence interactions that have been reported in open channels without subsurface flows.
Highlights
Landslides, volcanos, or anthropogenic changes may modify the availability of fine sediment in rivers, reservoirs, or lakes [1]
The sediment ejection generates a quasi-steady flow from the bed toward the water column, where the vertical velocity component is higher than the streamwise velocity component, i.e., the turbulent interactions in Q1 and Q3 for that structure has a higher probability than in other research
Low velocities in the streamwise direction and high vertical velocities can break the streamwise structures associated with secondary currents near the bed and sediment ejections can be seen
Summary
Landslides, volcanos, or anthropogenic changes may modify the availability of fine sediment in rivers, reservoirs, or lakes [1]. Fine sediment can cause pollution in gravel beds. The intrusion of fine sediment into gravel bed streams generates changes in the hyporheic exchange, nutrients cycling, low oxygenation of fish eggs, etc. The hyporreic zone have an important coupling between the subsurface groundwater system and surface water, such as rivers or lakes and floodplains. This exchange is through the porous sediment, and it is characterized by the circulation of surface water into the alluvium and back to the river bed [6]
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