AUTHOR=He Chang , Yin Zhen-Yu , Stocchino Alessandro , Wai Onyx Wing Hong 

TITLE=Generation of macro-vortices in estuarine compound channels

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1082506

DOI=10.3389/fmars.2023.1082506

ISSN=2296-7745

ABSTRACT=We report the results of a numerical investigation of the flow structure and mechanism of macro-vortices generation in estuarine compound channels. The Finite-Volume Coastal Ocean Model (FVCOM) was implemented to simulate tidal currents in compound channels, e.g. the Lantau-Channel, which lies in the middle of the Pearl River Estuary (PRE). Results showed that the velocity magnitude in channels was significantly larger than that of floodplains during ebb and flood phases, resulting in high velocity gradient at the depth discontinues. Vorticity and Q-criterion were used to analyse the macro-vortices distribution inside the PRE. Massive macro-vortices were generated along the compound channels where high vorticity were also detected. The across-estuary sections with single and multiple channels were selected as representatives to analyse velocity distribution during ebb and flood tide. To characterize the channel flow, the ratio of main channel depth of the Lantau-Channel to floodplain depth (R$_h$) was calculated using the topography information and surface elevation of sections. It was found that there existed channel segment where the flow periodically changed between shallow flow (R$_h>3$) and intermediate flow (2$<$R$_h<3$). This dynamic changing of R$_h$ greatly influenced the generation of macro-vortices. Transverse dispersive stresses were calculated to evaluate the longitudinal momentum transfer in the lateral direction. We found that the dispersive stresses could play an important role in the redistribution of momentum in addition to barotropic and baroclinic transport. This paper revealed the mechanism of dynamic generation of macro-vortices in estuarine compound channel, serving as a valuable example in understanding natural compound channel flows.