Modeling lateral circulation and its influence on the along-channel flow in a branched estuary

Zhu, Lei; He, Qing; Shen, Jian

doi:10.1007/s10236-017-1114-8

Cited by 23 publications

(26 citation statements)

References 54 publications

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“…This has led to shallow shoals in the groyne region and a deeper main channel in the middle of the NP, forming a typical channel‐shoal system. Cross‐channel flows have been observed in the NP through observational and numerical studies (Liu et al, ; Zhu et al, ). The NP is also the main mixing front of freshwater and saline water, resulting in strong horizontal salinity gradient and vertical stratification (Ge et al, , ; Wu et al, ).…”

Section: Study Site Observation Methods and Numerical Modelmentioning

confidence: 99%

“…Using a lateral momentum balance, they observed that stronger cross‐channel circulation by rotational effects (Coriolis and channel curvature) is larger during the ebb. A modeling study by Zhu et al () in a strongly anthropogenically impacted estuary (the Changjiang Estuary) suggests that lateral circulations are strong near the main navigation channel and peak close to slack tide conditions. This has great implications for siltation rates in the channel, in which more than 80 million m 3 /year (by 2011) needs to be dredged annually (Wang et al, ).…”

Section: Introductionmentioning

confidence: 99%

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

Zhou

Wang

et al. 2019

JGR Oceans

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Lateral flow significantly contributes to the near-bottom mass transport of salinity in a channel-shoal system. In this study, an integrated tripod system was deployed in the transition zone of a channel-shoal system of the Changjiang Estuary (CE), China, to observe the near-bottom physics with high temporal/spatial resolution, particularly focusing on the lateral-flow-induced mass transport. These in situ observations revealed a small-scale salinity fluctuation around low water slack during moderate and spring tidal conditions. A simultaneous strong lateral current was also observed, which was responsible for this small-scale fluctuation. A high-resolution unstructured-grid Finite-Volume Community Ocean Model has been applied for the CE to better understand the mechanism of this lateral flow and its impact on salinity transport. The model results indicate that a significant southward near-bed shoal-to-channel current is generated by the salinity-driven baroclinic pressure gradient. This lateral current affects the salinity transport pattern and the residual current in the cross-channel direction. Cross-channel residual current shows a two-layer structure in the vertical, especially in the intermediate tide when the lateral flow notably occurred. Both observation and model results indicate that near-bottom residual transport of water moved consistently southward (shoal to channel). Mechanisms for this intratidal salinity variation and its implications can be extended to other estuaries with similar channel-shoal features.Plain Language Summary In channel-shoal systems, lateral processes sometimes can be of great significance, for example, influencing salinity and sediment transport, even some biogeochemical matters that influence the water environment. Salinity and sediment transport will have a further effect on navigability, ecology, and so on, for example, sediment deposition issues, which significantly decrease the shipping capacity. Consequently, knowing the accurate information about the flow field and finding a criterion for pronounced lateral processes are important to better understand hydrodynamics and sediment behaviors in channel-shoal systems. Here in this study, we conducted an in situ observation and used numerical simulation to detect and predict a strong lateral flow in the North Passage of the Changjiang Estuary. This shoal-to-channel lateral flow occurred around the end of ebb and caused an intratidal salinity variation at the observation site, close to the deep channel. Therefore, a link between pronounced lateral flows and typical salinity variation can be established. This link can also be found in other estuaries like Hudson River estuary. Findings presented here will help to easily distinguish pronounced lateral flows and better understand the effect of lateral flows.

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Section: Study Site Observation Methods and Numerical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Zhou

Wang

et al. 2019

JGR Oceans

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“…The baroclinic force, generated by the transverse salinity gradient, drives a southward lateral flow in the main channel with a magnitude less than 0.05 m/s. The magnitude of lateral flow exceeds 0.2 m/s on the shoal, which is induced by the cross‐shoal flow (Zhu et al, ). During flood slack, the lateral flow is greater in magnitude than the along‐channel current and shows a two‐layer structure flow with the surface flow directs to the north and near‐bottom water flows southward.…”

Section: Resultsmentioning

confidence: 99%

Response of Stratification Processes to Tidal Current Alteration due to Channel Narrowing and Deepening

Zhu

Shen

2020

JGR Oceans

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Stratification in estuaries has received much focus due to its importance in estuarine hydrodynamics and material transport. By utilizing a well‐calibrated numerical model, in this work we investigate the changes in stratification in the deepened and narrowed North Passage of the Changjiang Estuary. Before channel narrowing and deepening, lateral straining, generated by the interaction between vertical shear in lateral flow and transverse salinity gradient, is the dominant factor that controls stratification. A two‐layer structure of the lateral flow strains the isopycnal transversely, resulting in rapid stratification from late flood to early ebb tide. Thus, maximum stratification occurs during the early ebb. Then, the stratification was suppressed by the vertical mixing and the less stratified water advected from upstream, even the vertical shear in along‐channel flow continued to strain the isopycnal. After channel deepening and narrowing, the salinity in the upper water column experienced a sharp vertical gradient during the entire tidal cycle, while the transverse salinity gradient and lateral flow are profoundly reduced. The impact of lateral straining on stratification becomes minor. The enhanced stratification results in a sharp decrease in turbulent mixing within the pycnocline. The water movement in the upper layer is in a free‐stream status and the tidal current speed increases significantly. The alteration of the vertical current structure enhances the along‐channel tidal straining and stratification is most vigorous on late ebb tide.

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“…Wave energy is moderate at the mouth with a mean wave height of 0.9 m, although wave heights can reach 6.2 m during storm conditions (Yang et al, 2001). Under combined river and tidal forcing, the mouth zone of the YE is a partially mixed environment with strong density currents and lateral circulations due to water exchange between different branches (Wu et al, 2010;Zhu et al, 2018). These lateral circulations, however, are presently decreasing because of elevated tidal flats and the blocking effects of the jetties discussed in the next paragraphs .…”

Section: Study Areamentioning

confidence: 99%

Decadal morphological evolution of the mouth zone of the Yangtze Estuary in response to human interventions

Zhu

Guo

Maren

et al. 2019

Earth Surf Processes Landf

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The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi‐natural system to evaluate large‐scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be >30 years (starting from the mid‐1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large‐scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd.

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Modeling lateral circulation and its influence on the along-channel flow in a branched estuary

Cited by 23 publications

References 54 publications

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

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

Response of Stratification Processes to Tidal Current Alteration due to Channel Narrowing and Deepening

Decadal morphological evolution of the mouth zone of the Yangtze Estuary in response to human interventions

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