Aerial Observations and Numerical Simulations Confirm Density‐Driven Streamwise Vortices at a River Confluence

Abstract

The hydrodynamics of river confluences is a fascinating subject having attracted the attention of inquisitive minds for centuries (da Vinci & MacCurdy, 2009). The coherent flow structures generated within a confluence are key drivers of mixing and sediment transport. The roles of shear-induced vertically orientated Kelvin-Helmholtz (KH) instabilities (

Impact of Density Gradients on the Secondary Flow Structure of a River Confluence

“…The validation, detailed in Duguay et al. (2022), supports that the numerical approach could accurately reproduce the mean surface velocity field measured by large‐scale particle image velocimetry and velocity profiles. The model was also validated against metrics derived from the aerial drone video taken on 9 July 2020, specifically the location and spatial scales of the primary streamwise orientated vortices and the frequencies and lateral scales of the large‐scale episodic pulses (see Figures 6 and 7 of Duguay et al.…”

“…The model was validated with field measurements obtained on 22 October 2020. The validation, detailed in Duguay et al (2022), supports that the numerical approach could accurately reproduce the mean surface velocity 2022)). These validations establish confidence in the model's ability to provide insights into coherent flow structure formation and interactions.…”

“…2020 (see Duguay et al. (2022)). Water surface elevation was 0.07 m higher on 9 July than on 22 October 2020.…”

“…The model was also validated against metrics derived from the aerial drone video taken on 9 July 2020, specifically the location and spatial scales of the primary streamwise orientated vortices and the frequencies and lateral scales of the large‐scale episodic pulses (see Figures 6 and 7 of Duguay et al. (2022)). These validations establish confidence in the model's ability to provide insights into coherent flow structure formation and interactions.…”

“…SOVs were first discovered in numerical models as a pair of back-to-back, counter-rotating SOVs flanking each side of the mixing interface (Constantinescu et al, 2011) and their development is generally attributed to the downwelling of superelevated water, in a process strengthened by planform curvature (Sukhodolov & Sukhodolova, 2019). Recently, however strongly coherent SOVs were directly observed in turbidity currents at the Coaticook-Massawippi confluence (Duguay et al, 2022), and numerical modeling showed these SOVs to be gravity currents, caused by a small density gradient Δρ of ≈0.5 kg/m 3 , being confined between the converging flows (Duguay et al, 2022). Gaining knowledge of how greater magnitudes of Δρ and/or a reversal in the direction of Δρ influence these SOVs is the first step towards a full understanding of these intriguing flow structures.Density gradients develop when differences in temperature, dissolved minerals, or suspended sediment concentrations are present across the mixing interface.…”