Longitudinal variation in lateral trapping of fine sediment in tidal estuaries: observations and a 3D exploratory model

Abstract

This study investigates the longitudinal variation of lateral entrapment of suspended sediment, as is observed in some tidal estuaries. In particular, field data from the Yangtze Estuary are analysed, which reveal that in one cross-section, two maxima of suspended sediment concentration (SSC) occur close to the south and north sides, while in a cross-section 2 km downestuary, only one SSC maximum on the south side is present. This pattern is found during both spring tide and neap tide, which are characterised by different intensities of turbulence. To understand longitudinal variation in lateral trapping of sediment, results of a new three-dimensional exploratory model are analysed. The hydrodynamic part contains residual flow due to fresh water input, density gradients and Coriolis force and due to channel curvature-induced leakage. Moreover, the model includes a spatially varying eddy viscosity that accounts for variation of intensity of turbulence over the spring-neap cycle. By imposing morphodynamic equilibrium, the two-dimensional distribution of sediment in the domain is obtained analytically by a novel procedure. Results reveal that the occurrence of the SSC maxima near the south side of both crosssections is due to sediment entrapment by lateral density gradients, while the second SSC maximum near the north side of the first cross-section is by sediment transport due to curvature-induced leakage. Coriolis deflection of longitudinal flow also contributes the trapping of sediment near the north side. This mechanism is important in the upper estuary, where the flow due to lateral density gradients is weak.

Study of Lateral Flow in a Stratified Tidal Channel‐Shoal System: The Importance of Intratidal Salinity Variation

“…Cross‐sectional flows influence the salinity, leading to an intratidal salinity variation (ISV). Many studies have identified the salinity's response to the longitudinal and vertical process (Bowen, ; Chen & de Swart, ; Dyer, ; Simpson et al, ). However, few observations directly relate salinity fluctuations to lateral flows.…”

Hydrodynamics Sabang Bay and Its Influence on Near Shore Sediment Transport, Weh Island, Indonesia

“…In contrast, in the surface bottom, the velocity of current becomes weaker ranging from -0.3-0.4 m/s caused by the many factors such as bottom friction, the higher value of density, and some other forces (Van Rijn, 2011). If we see in more detail, the tidal ellipses that rotate counterclockwise bottomward show the influence of Coriolis forces (Chen & de Swart, 2018). This event also determines that the Ekman spiral principal controls the vertical transport that occurred in Sabang Bay.…”

“…On the other hand, during 20-year tidal prediction, we also identified the lowest water level during spring tidal conditions of 1.86 meters beneath MSL, while, the average minimum surface level during spring tidal conditions is 1.34 meters, with the lowest value of 0.91 meters beneath MSL. The variability of surface elevation changes has a role in generating surface currents and transport mechanisms in the estuarine area (Chen & de Swart, 2018). The higher the elevation formed, the more substantial transport energy resulted from this tidal fluctuation (Qarnain et al, 2014).…”

Regime shifts in the Changjiang (Yangtze River) Estuary: The role of concentrated benthic suspensions

“…The lateral flow asymmetry in the North Passage results from lateral density gradients and the curvature effect (Chen and de Swart, 2018;Zhu et al, 2018;Zhou et al, 2019). Due to the lateral flow asymmetry, the CBS pool tends to move to the south flank of the channel, especially when sediment settles from the CBS to the bed (Fig.…”