Author(s): Stan Thorez; Ulrich Lemmin; D. Andrew Barry; Koen Blanckaert
Linked Author(s): Koen Blanckaert, Ulrich Lemmin
Keywords: Hyperpycnal inflows; Plunging; Vortex dynamics; Turbulent mixing processes
Abstract: Hyperpycnal (negatively buoyant) river inflows plunge into lakes or reservoirs upon entry, producing gravity-driven underflows along the bed (Fischer et al., 1979; Forel, 1885). If such underflows encounter a layer of equal density within the water column, they detach from the bed and form an interflow. The amount of mixing between river-borne water and ambient water conditions the density excess and thus the interflow depth of these flows. As they are vectors for sediment, nutrients, oxygen and contaminants, their pathway and destination have an impact on the water quality and hazards in lakes and reservoirs, highlighting the importance of studying the mixing processes these flows undergo. Previous research has pointed out that the mixing processes of the near-shore plunging region are of particular importance. The plunging mixing has been quantified in the literature using the plunging mixing coefficient Ep (Akiyama & Stefan, 1984; Ford & Johnson, 1983): Ep = Qd/Q0 - 1 (1) in which Q0 and Qd signify the discharge at the inflow and directly downstream of the plunging region, respectively. It has been shown that the quantity of plunging mixing in laterally confined inflows, typical for reservoirs in which valley walls inhibit lateral motion, can be up to an order of magnitude smaller (e.g. Johnson et al., 1989; Ep = O(0.1)) than that in unconfined inflows, typical for lakes (Blanckaert et al., 2024; Thorez et al., 2024; Ep = O(1)). This raises the question: do unconfined inflows exhibit hydrodynamic mixing processes absent in confined inflows, and if so, what are they?
Year: 2025