Impacts of Tidal Flat Reclamation on Saltwater Intrusion and Freshwater Resources in the Changjiang Estuary

Lyu, Hanghang; Zhu, Jianrong

doi:10.2112/jcoastres-d-18-00077.1

Cited by 18 publications

(13 citation statements)

References 27 publications

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“…Residual water levels, including those under climatic wind conditions (Figure 3b) and the persistent strong wind in February 2014, were calculated using the results of a large domain (Bohai Sea, Yellow Sea, and East China Sea) numerical model (Wu et al, 2011). More details on the model boundary and initial conditions are provided by Lyu and Zhu (2019). Water depths measured in 2014 were used in the model.…”

Section: Methodsmentioning

confidence: 99%

“…Maritime transportation typically requires the construction of channels, ports, and other structures to minimize navigational hazards. Such human interventions significantly alter the morphology and therefore have great impact on the tides (Chant et al, 2018), flood (Ralston et al, 2019), and saltwater intrusion (C. Liu et al, 2019; Lyu & Zhu, 2019). The impact on saltwater intrusion is crucial for urban estuaries, as it affects drinking water supply for large number of population.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Dikes on Saltwater Intrusion Under Various Wind Conditions in the Changjiang Estuary

Zhu

Chant

et al. 2020

JGR Oceans

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To improve navigation, the deep waterway project (DWP) was implemented in the North Passage of the Changjiang Estuary in 1998, which includes a deep channel and two dikes protecting it. By altering estuarine morphology, the DWP can affect saltwater intrusion and mixing, with implications for drinking water intake and supply. In this study, we employ a numerical model to study the influence of dikes of the DWP on saltwater intrusion in the estuary under the climatic and persistent strong northerly wind conditions that occurred in February 2014. The model results show that the dikes prevent the southward transport of relatively low‐salinity water at the mouth of the North Channel (NC) under climatic wind conditions, resulting in the weakening of saltwater intrusion and mixing in this channel. Under persistent strong northerly wind conditions, relatively high‐salinity water is transported southward to the mouth of NC and blocked by the dikes causing a water level rise at the mouth of the NC. As a result, a large amount of high‐salinity water advected into the NC and then out to the sea from the South Chanel, forming a counterclockwise horizontal circulation. The salinity increases abnormally, but mixing decreases in the NC for no more salinity variance input with the implementation of the DWP. Overall, the DWP favors water intake for the reservoir in NC under climatic wind conditions and is unfavorable to water intake under persistent strong northerly winds (>9 m/s), which can lead to extremely severe saltwater intrusion.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Dikes on Saltwater Intrusion Under Various Wind Conditions in the Changjiang Estuary

Zhu

Chant

et al. 2020

JGR Oceans

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“…The transaction was located at the landward boundary of the turbidity maximum zone in the Yangtze Estuary. The barotropic pressure gradient caused by the huge river discharge of the Yangtze River made the variation range of salinity on surface layer significantly less than bottom within a tidal cycle [42]. With the variation of salinity on bottom, the stratification of water columns increased during flood tide and decreased during ebb tide (Figures 2 and 5).…”

Section: Mechanism Behind Lateral Variations Of Tidal Mixing Asymmetrymentioning

confidence: 99%

Lateral Variation of Tidal Mixing Asymmetry and Its Impact on the Longitudinal Sediment Transport in Turbidity Maximum Zone of Salt Wedge Estuary

Teng

Cheng

Zhang

et al. 2022

JMSE

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The lateral bathymetry in the estuary results in different degrees of tidal mixing asymmetry, which has significant impacts on the longitudinal sediment transport by changing the temporal variation of vertical eddy diffusion. This study focus on the lateral variation of tidal mixing asymmetry and longitudinal sediment transport at the landward boundary of turbidity maximum zone in the North Channel of Yangtze estuary, which is a typical time-dependent salt wedge estuary. A transect survey was carried out in December, 2018; five vertical profiles of flow velocity, salinity and suspended sediment concentration were simultaneously measured covering a spring tidal cycle. Analysis of the data revealed that, after the maximum ebb, the stratification in the main and secondary channel was stronger than that on the shoal. In the channel, during ebb tide, the stronger stratification restrained the turbulent mixing induced by vertical shear, vertical mixing during the flood tide was stronger than that during ebb tide and vertical mixing coefficients ranged from 0.06 to 0.12, showing regular tidal mixing asymmetry over a flood–ebb tidal cycle. Therefore, stronger eddy diffusion caused by vertical mixing resulted in higher suspended sediment concentrations during flood tide, the larger landward tidally averaged sediment transport rate was induced by tidal pumping with the transportation of flood tidal current and the net sediment transport over a flood–ebb tidal cycle in the channel was landward. Meanwhile, on the shoal, under the effect of vertical shear, the vertical mixing during flood tide was weaker than that during ebb tide; vertical mixing coefficients ranged from −0.27 to −0.02, showing the reversed tidal mixing asymmetry. Higher suspended sediment concentration was transported seaward by the ebb current, the tidally averaged sediment transport rate by both tidal pumping and advection was seaward and the net sediment transport was seaward. Furthermore, large river discharge increased the seaward advection sediment flux on the surface layer in the main channel, resulting in the seaward tidally averaged sediment flux. Strong resuspension increased the seaward advection sediment flux near the bottom in the main and secondary channel, resulting in the seaward tidally averaged sediment flux.

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“…1b) for the demands of land and water. These projects considerably changed the local topography and further changed the topography in the entire estuary by altering the hydrodynamic processes (Lyu and Zhu, 2018a;Zhu and Bao, 2016). Due to these anthropogenic activities, the Changjiang Estuary has undergone dramatic topography change from 2007 to 2017.…”

Section: Topography Change From 2007 To 2017mentioning

confidence: 99%

“…River discharge and tides are major control factors of saltwater intrusion in the Changjiang Estuary (Li et al, 2010;Qiu et al, 2012;Shen et al, 2003;Wu et al, 2006;Zhu et al, 2010;) but is also influenced by wind (Li et al, 2012), topography (Li, et al, 2014), anthropogenic activities in the river basin and estuary (Lyu and Zhu, 2018a;Qiu and Zhu, 2013;Zhu, et al, 2006) and sea-level rise (Qiu and Zhu, 2015). The North Branch is always found to be filled with highly saline water due to a low river discharge and high tidal range.…”

Section: Introductionmentioning

confidence: 99%

Impacts of topography change on saltwater intrusion over the past decade in the Changjiang Estuary

Chen

Zhu

Lyu

et al. 2019

Estuarine, Coastal and Shelf Science

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Saltwater intrusion in estuaries is mainly controlled by tides and river discharge, as well as by topography and other factors. The Changjiang estuary has been seen a significant change in its topography from the data obtained in 2007 and 2017. In this study, a well-validated 3D numerical model was used to simulate and analyze the residual water and salt transport, water diversion ratio (WDR) in bifurcated channels and water resources in the Changjiang Estuary in 2007 and 2017. The comparisons of the model results showed that due to the North Branch becoming much shallower and narrower over the period from 2007 to 2017, the overall salinity in the North Branch decreased and the intensity of saltwater spillover (SSO) from the North Branch into the South Branch weakened. In the North Channel, the simulated residual or net transection water flux (NTWF) and WDR decreased during spring tides, resulting in increased saltwater intrusion. During neap tides, the saltwater intrusion was weakened despite the decreased NTWF and WDR because the water depth at the river mouth became shallower. The changes of topography during that period also resulted in changes of DWR, NTWF, salt transport across the tidal flats and dykes in the North Passage, South Passage and the South Channel, as well as overall dynamic mechanism. The results indicated that the salinity at the water intakes of the three reservoirs in the estuary slightly decreased, indicating that the time that reservoirs can take water from the estuary become longer in dry seasons. In the scenario of complete silt-up of the North Branch, the saltwater intrusion was weakened in the South Branch because of the disappearance of the SSO, which was favorable for the utilization of freshwater resources, but enhanced in the North Channel, North and South Passages. The overall influence from the topographic change over the period is that the saltwater intrusion is weakened in the North Branch, and enhanced during spring tides and weakened during neap tides in the North Channel, North and South Passages. Sediment accretion in the North Branch is favorable for utilization of freshwater resources.

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Impacts of Tidal Flat Reclamation on Saltwater Intrusion and Freshwater Resources in the Changjiang Estuary

Cited by 18 publications

References 27 publications

Effect of Dikes on Saltwater Intrusion Under Various Wind Conditions in the Changjiang Estuary

Effect of Dikes on Saltwater Intrusion Under Various Wind Conditions in the Changjiang Estuary

Lateral Variation of Tidal Mixing Asymmetry and Its Impact on the Longitudinal Sediment Transport in Turbidity Maximum Zone of Salt Wedge Estuary

Impacts of topography change on saltwater intrusion over the past decade in the Changjiang Estuary

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