Abstract
A confluence is a natural component in river and channel networks. This study deals, through field and numerical studies, with alluvial behaviors of a confluence affected by both river run-off and strong tides. Field measurements were conducted along the rivers including the confluence. Field data show that the changes in flow velocity and sediment concentration are not always in phase with each other. The concentration shows a general trend of decrease from the river mouth to the confluence. For a given location, the tides affect both the sediment concentration and transport. A two-dimensional hydrodynamic model of suspended load was set up to illustrate the combined effects of run-off and tidal flows. Modeled cases included the flood and ebb tides in a wet season. Typical features examined included tidal flow fields, bed shear stress, and scour evolution in the confluence. The confluence migration pattern of scour is dependent on the interaction between the river currents and tidal flows. The flood tides are attributable to the suspended load deposition in the confluence, while the ebb tides in combination with run-offs lead to erosion. The flood tides play a dominant role in the morphodynamic changes of the confluence.
Highlights
A river confluence is a key feature of a drainage basin in terms of hydrology and geomorphology, for geological records, as well as from a habitat point of view [1]
In a river confluence subjected to strong tidal currents, its flow and morphological changes are dependent on a number of factors, showing a complex pattern in both time and space
From the sea into the Yong River, the sediment is transported by the tidal currents, especially during the spring tides
Summary
A river confluence is a key feature of a drainage basin in terms of hydrology and geomorphology, for geological records, as well as from a habitat point of view [1]. In a long-term perspective, the flow patterns govern the morphology changes of the confluence, e.g., the scouring and sediment deposition [2]. In bi-directional flows, the shift of the dominant processes between river run-off and tides, featuring periodical changes in both magnitude and direction, induces more degrees of complexity in terms of flow patterns, sediment transport, and bed morphology change in the confluence. The objective was, by means of field measurements and simulations, to provide insight into the physical phenomenon that governs flow features of the tidal confluence, to describe circulatory patterns of suspended load transport, and to predict the scour-hole evolution. The paper includes a description of the study area, field measurements of flow and sediment and data analyses, numerical formulation, model set-up with calibration and validation, major flow features, and morphological changes of the confluence
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