Author(s): Stan Thorez; Ulrich Lemmin; Andrew Barry; Koen Blanckaert
Linked Author(s): Ulrich Lemmin, Koen Blanckaert
Keywords: Hyperpycnal inflows; Plunging; Gravity currents; Mixing processes
Abstract: When a river entering a lake or reservoir is denser than the receiving body of water, it will plunge and form a gravity-driven current (underflow) near the bed. When a layer of equal density is encountered, these underflows will detach from the bed and intrude horizontally into the lake waters to form an interflow. Alternatively, they may continue to the bottom of the lake. As underflows carry a number of constituents fed to them by the river or eroded from the bed, such as sediment, contaminants, nutrients and oxygen, their pathway and final destination has an impact on lake water quality. Turbulent mixing processes dilute the excess density of the river plume (as compared to the ambient lake water) and thereby exert a primary control on the final intrusion depth. Quantifying these turbulent mixing as a function of the inflow conditions is therefore key. The focus of this contribution is on the mixing processes in the plunging region, which are known to be of dominant importance (Rueda et al., 2007). In the past, most estimations of the amount of mixing in the plunging region were performed in laterally confined lab experiments and/or through passive tracer methods. In this study, an effort was made (a) to quantify the mixing in the plunging region directly from flow velocities in a laterally unconfined inflow in the field and (b) to investigate the influence of the inflow conditions on this mixing.
Year: 2024