Flow Structures and Their Controls on Downstream Discharge Regulation for a Combined Confluence and Bifurcation Network Node

Abstract A deep understanding of flow regulation in river bifurcations is critical for downstream river management and flood control. The deltaic river network frequently contains the H‐shaped network node, where two main channels are linked together via a connecting channel, combining both bifurcation and confluence. However, flow structures and their control on downstream discharge regulation of the H‐shaped node remain unclear in river hydraulics. This study employed a high‐resolution hydrodynamic model to simulate the flow dynamics of the H‐shaped node in the Pearl River network, revealing three major findings: (a) the H‐shaped node produces a more uniform discharge distribution between downstream channel branches than a single bifurcation; (b) the connecting channel plays a core role in downstream discharge regulation. When the upstream discharge ratio (UDR) exceeds a threshold (ranging between 3 and 4 in this study), the surface elevation difference between two junctions of the connecting channel causes the through flow to reverse its flow direction; (c) the switching of flow direction results in a dynamic transition between confluence‐type and bifurcation‐type flow structures at the two junctions. For , the vortices developed at the tail of the island upstream of the junction can adjust the discharge supply to the connecting channel, which can serve as a stabilizing effect on river channel bifurcations. Further analyses reveal that the dynamic response of flow structures to UDR reflects their core role in discharge regulation, thus functioning as naturally occurring water diversion facilities analogous to training dams and sluice gates. This study not only highlights the potential of the H‐shaped node as an efficient flood control node, but also provides scientific basis for the design of nature‐based, cost‐effective diversion facilities in the deltaic river system.