Formation of Turbidity Maximum in the Modaomen Estuary of the Pearl River, China: The Roles of Mouth Bar

Abstract

An estuarine turbidity maximum (ETM) functions as a filter and plays a key role in transporting suspended sediment. The features of ETM and their formation mechanisms vary with different types of estuaries. Their responses to morphological factors require further study. In this study, the Modaomen Estuary of the Pearl River was selected to examine the formation mechanisms of the ETM and roles of the mouth bar. Hydrodynamics, suspended sediment concentration, and sediment size distribution were measured via cruise shipboard in the mouth bar zone during the dry season of 2020, which indicated that the ETM occurred in the central and western bars. Furthermore, numerical modeling of an idealized estuary based on Delft3D was performed to explore the effects of the existence of a mouth bar on the dynamic structures causing the ETM, including saltwater intrusion, residual longitudinal circulation, and bed sediment resuspension. The results indicated that the existence of a mouth bar contributed to the occurrence of double residual circulations and enhanced bed shear stress on the mouth bar, which favor the ETM formation. In general, two different dynamic regimes were responsible for the ETM formation, that is, sediment trapping by saltwater intrusion and sediment resuspension induced by tidal currents. The mouth bar played a key role in these two mechanisms, including altering the estuarine circulation and bed shear stress. The results contribute to a better elucidation of the ETM formation in estuaries and provide scientific guidelines for estuarine management and engineering.

Flood-driven jet flow and sedimentary regime in a river-dominated estuary

“…Due to the lack of bathymetric data before and after the flood in the ME, which caused the absence of validation of morphological changes, the simulation results were compared with those of previous studies. Li et al (1993) and Jia et al (2018) showed that during the flood season, the west channel of the ME experienced slight erosion, whereas the east channel was dominated by deposition. At the central mouth bar, erosion and deposition occurred simultaneously, with deposition dominating the crest and outer slope of the mouth bar, and erosion dominating its inner slope.…”

Analysis of influencing factors of seawater intrusion in the Yangtze River Estuary and control for water supply security

“…Tides and currents are the power source of the mixing of seawater and freshwater, caused by the gravitational forces of celestial bodies, and they have a crucial impact on seawater intrusion (Paiva and Schettini, 2021). The effects of tides and currents on seawater intrusion include: the convective transport of currents, turbulent mixing caused by tides, and the combined effect of tides and topography leading to tidal trapping and tidal transport (Li et al, 2022). Wind also has a significant impact on seawater intrusion (Tao et al, 2020).…”