Journal Article

Three-Dimensional Hydrodynamics and Morpho-dynamics at a Tidal River Junction

Hu, Lihan, Xu, Jin, Han, Jianjun, Wang, Lingling

2024

Overview

River junctions act as critical nodes in river networks because they can affect flows, sediment transports, and morphological and ecological patterns. River junctions subject to the unidirectional flow have been widely studied in the last decades; in contrast, the efforts are limited regarding the understanding of flow behaviors and morphological changes around tidal river junctions. In this study, a numerical model coupling two- and three-dimensional (2D-3D) domains is established to study the flow patterns and sediment motion of the tidal reach of Rongjiang River (RR), which has a typical tidal river junction. The simulation results show that the continuous process of alternating merging and separating streams leads to the swing of flow dynamic axes in the planar field, and results in the periodic inversion of secondary flows (helical flows) around the junction. These features are unique and different from the hydrodynamics of fluvial junctions. Moreover, a simulation of the particle moving indicates that the periodic 3D circulation around the junction can make the suspended sediment tend to gather in the north branch, which leads to the net input of the sediment into the north branch. Additionally, the long-term morphological evolutions and potential changes are analyzed by historical data and a numerical experiment. The numerical experiment results illustrate the significant sedimentation at river banks and deepening at mid-channels under the effects of tidal currents, which also demonstrates that the net sediment input to the tributary is a potential cause and mechanism of the distinct bed discordance in tidal river junctions. Furthermore, these findings emphasize the importance of periodical flow behaviors and local hydraulics on the dynamics around the tidal river junctions, which can expand the understanding of physics both in tidal and non-tidal river reaches and provide a reference for tidal river management.

• Publisher: Springer Nature B.V
• Subject: Creeks & streams / Discordance / Flow distribution / Flow pattern / Fluid flow / Fluid mechanics / Helical flow / History / Hydraulics / Hydrodynamics / Mathematical models / Morphology / Numerical models / Physics / River banks / River networks / Riverbanks / Rivers / Secondary flow / Sediment / Sediments / Suspended sediments / Tidal currents / Tidal effects / Tidal rivers / Tidal waterways / Unidirectional flow