scholarly journals Dynamic mechanism of an extremely severe saltwater intrusion in the Changjiang estuary in February 2014

2020 ◽  
Vol 24 (10) ◽  
pp. 5043-5056
Author(s):  
Jianrong Zhu ◽  
Xinyue Cheng ◽  
Linjiang Li ◽  
Hui Wu ◽  
Jinghua Gu ◽  
...  
Keyword(s):  
Water Level ◽  
Water Transport ◽  
River Discharge ◽  
Saltwater Intrusion ◽  
Changjiang Estuary ◽  
Maximum Speed ◽  
Residual Water ◽  
Northerly Wind ◽  
The Changjiang Estuary ◽  
Water Level Rise

Abstract. Estuarine saltwater intrusions are mainly controlled by river discharge and tides. Unexpectedly, an extremely severe saltwater intrusion event occurred in February 2014 in the Changjiang estuary under normal river discharge conditions. This intrusion cut off the freshwater input for 23 d into the Qingcaosha reservoir, which is the largest estuarine reservoir in the world, creating a severe threat to water safety in Shanghai. No similar catastrophic saltwater intrusion has occurred since records of salinity in the estuary have been kept. During the event, a persistent and strong northerly wind existed, with a maximum speed of 17.6 m s−1, lasting 9 d and coinciding with a distinct water level rise. Our study demonstrates that the extremely severe saltwater intrusion was caused by this northerly wind, which drove substantial landward net water transport to form a horizontal estuarine circulation that flowed into the northern channel and out of the southern channel. This landward net water transport overpowered the seaward-flowing river runoff and transported a large volume of highly saline water into the northern channel. The mechanisms of this severe saltwater intrusion event, including the northerly wind, residual water level rise, landward water transport and resulting horizontal circulation, etc., were systematically investigated.

scholarly journals Dynamic mechanism of extremely severe saltwater intrusion in the Changjiang Estuary occurred in February 2014

2020 ◽  
Author(s):  
Jianrong Zhu ◽  
Linjiang Li ◽  
Hui Wu ◽  
Jinghua Gu ◽  
Hanghang Lyu ◽  
...  
Keyword(s):  
River Discharge ◽  
Saltwater Intrusion ◽  
Changjiang Estuary ◽  
Dynamic Mechanism ◽  
Ekman Transport ◽  
Maximum Speed ◽  
Northerly Wind ◽  
The Changjiang Estuary ◽  
The North ◽  
Freshwater Resource

Abstract. Estuarine saltwater intrusion is mainly controlled by river discharge and tide. Unexpectedly, an extremely severe saltwater intrusion event in February 2014 occurred in the Changjiang Estuary under normal river discharge conditions. It cut off the freshwater input for 23 days into the Qingcaosha Reservoir, which is the largest estuarine reservoir in the world, creating a severe threat to water safety in Shanghai. Such catastrophic saltwater intrusion has not occurred since recorded salinity in the estuary. During the event, a persistent and strong northerly wind existed, with a maximum speed of 16 m s−1, lasting ten days and coinciding with a distinct water level rise. Our study demonstrates that this extremely severe saltwater intrusion was caused by a persistent and strong northerly wind, which drove substantial landward Ekman transport to form a horizontal estuarine circulation that flowed into the North Channel and out of the South Channel. This process surpassed seaward runoff and brought very large amounts of highly saline water into the upper reaches in the North Channel. An ordinary cold front passing over the estuary cannot produce strong saltwater intrusion; only a strong northerly wind lasting 8 days can produce a severe saltwater intrusion in the Changjiang Estuary. The revealed dynamic mechanism is important to ensure safety of freshwater resource utilization in estuaries.

scholarly journals Seasonal behaviour of tidal damping and residual water level slope in the Yangtze River estuary: identifying the critical position and river discharge for maximum tidal damping

2019 ◽  
Vol 23 (6) ◽  
pp. 2779-2794 ◽  
Author(s):  
Huayang Cai ◽  
Hubert H. G. Savenije ◽  
Erwan Garel ◽  
Xianyi Zhang ◽  
Leicheng Guo ◽  
...  
Keyword(s):  
Water Level ◽  
River Discharge ◽  
Yangtze River ◽  
River Estuary ◽  
Yangtze River Estuary ◽  
Residual Water ◽  
The Yangtze River ◽  
The Yangtze River Estuary ◽  
Seasonal Behaviour ◽  
Residual Water Level

Abstract. As a tide propagates into the estuary, river discharge affects tidal damping, primarily via a friction term, attenuating tidal motion by increasing the quadratic velocity in the numerator, while reducing the effective friction by increasing the water depth in the denominator. For the first time, we demonstrate a third effect of river discharge that may lead to the weakening of the channel convergence (i.e. landward reduction of channel width and/or depth). In this study, monthly averaged tidal water levels (2003–2014) at six gauging stations along the Yangtze River estuary are used to understand the seasonal behaviour of tidal damping and residual water level slope. Observations show that there is a critical value of river discharge, beyond which the tidal damping is reduced with increasing river discharge. This phenomenon is clearly observed in the upstream part of the Yangtze River estuary (between the Maanshan and Wuhu reaches), which suggests an important cumulative effect of residual water level on tide–river dynamics. To understand the underlying mechanism, an analytical model has been used to quantify the seasonal behaviour of tide–river dynamics and the corresponding residual water level slope under various external forcing conditions. It is shown that a critical position along the estuary is where there is maximum tidal damping (approximately corresponding to a maximum residual water level slope), upstream of which tidal damping is reduced in the landward direction. Moreover, contrary to the common assumption that larger river discharge leads to heavier damping, we demonstrate that beyond a critical value tidal damping is slightly reduced with increasing river discharge, owing to the cumulative effect of the residual water level on the effective friction and channel convergence. Our contribution describes the seasonal patterns of tide–river dynamics in detail, which will, hopefully, enhance our understanding of the nonlinear tide–river interplay and guide effective and sustainable water management in the Yangtze River estuary and other estuaries with substantial freshwater discharge.

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

2019 ◽  
Vol 231 ◽  
pp. 106469 ◽  
Author(s):  
Qing Chen ◽  
Jianrong Zhu ◽  
Hanghang Lyu ◽  
Shunqi Pan ◽  
Shenliang Chen
Keyword(s):  
Saltwater Intrusion ◽  
Changjiang Estuary ◽  
The Changjiang Estuary ◽  
The Past

Types of saltwater intrusion of the Changjiang Estuary

2001 ◽  
Vol 44 (S1) ◽  
pp. 150-157 ◽  
Author(s):  
Zhichang Mao ◽  
Huanting Shen ◽  
T. James Liu ◽  
D. Eisma
Keyword(s):  
Saltwater Intrusion ◽  
Changjiang Estuary ◽  
The Changjiang Estuary

scholarly journals Impacts of the Qingcaosha Reservoir on saltwater intrusion in the Changjiang Estuary

2021 ◽  
Vol 4 (1) ◽  
pp. 17-35
Author(s):  
Zhangliang Ding ◽  
Jianrong Zhu ◽  
Hanghang Lyu
Keyword(s):  
Saltwater Intrusion ◽  
Neap Tide ◽  
Spring Tide ◽  
Changjiang Estuary ◽  
Water Diversion ◽  
The Changjiang Estuary ◽  
The North ◽  
Salinity Increase ◽  
Hydrodynamic Processes ◽  
Changxing Island

The massive Qingcaosha Reservoir (QCSR) is located in the Changjiang Estuary along the northwest coast of Changxing Island. The reservoir significantly narrowed the upper reaches of the North Channel and deepened the channel near the reservoir. These topographical changes inevitably influenced hydrodynamic processes and saltwater intrusion in the estuary. A well-validated model was employed to investigate the influence of the QCSR on saltwater intrusion in the Changjiang Estuary. The model results showed that the narrowed upper reaches of the North Channel decreased the water diversion ratio and thus increased salinity in the North Channel. During the moderate tide after neap tide, the salinity decreased at the water intake of the QCSR because saltwater intrusion was obstructed at flood slack at the surface, while the salinity increase during the moderate tide after spring tide was mainly due to the intensified saltwater intrusion during spring tide. The deepening of the channel near the QCSR resulted in an increased water diversion ratio, and the salinity in the Eastern Chongming Shoal decreased by more than 0.5 psu during spring tide; however, the saltwater intrusion was enhanced due to the strengthened baroclinic force, which is proportional to the water depth. During neap tide, the salinity in the entire North Channel decreased because of a 1.4% increase in the water diversion ratio of the North Channel and the relatively weak tide.

scholarly journals IMPACTS OF DEEP WATERWAY PROJECT ON LOCAL CIRCULATIONS AND SALINITY IN THE CHANGJIANG ESTUARY, CHINA

2011 ◽  
Vol 1 (32) ◽  
pp. 44 ◽  
Author(s):  
Jianzhong Ge ◽  
Pingxing Ding ◽  
Changsheng Chen
Keyword(s):  
Saltwater Intrusion ◽  
Unstructured Grid ◽  
Model Simulation ◽  
High Tide ◽  
Changjiang Estuary ◽  
Observation Data ◽  
Three Dimension ◽  
Local Circulation ◽  
The Changjiang Estuary ◽  
Astronomical Tide

With an aim to improve and maintenance water depth along the navigational channel, the Deep Waterway Project has been conducted in the Changjiang Estuary. The structures of dikes and groins have greatly changed the local circulation with the combined effects of astronomical tide and strong freshwater discharge. A high-resolution fully three-dimension unstructured-grid model (FVCOM) has been applied to study the complicated hydrodynamics with the implementation of unstructured-grid dike-groin module. With the model validation with observation data, the simulation shows the dikes and groins has converted the rotational current into reciprocating flow along the navigational channel between the dikes, and produced the geometrically controlled eddies. The significant southward crossover current was produced along the dike during high tide when the water level is higher than the dike height. The strong saltwater intrusion is also revealed in the observation and model simulation.

scholarly journals Water and Salt Transports in the Hengsha Channel of Changjiang Estuary

2022 ◽  
Vol 10 (1) ◽  
pp. 72
Author(s):  
Rui Ma ◽  
Jianrong Zhu
Keyword(s):  
Water Transport ◽  
Neap Tide ◽  
Spring Tide ◽  
Dry Season ◽  
Changjiang Estuary ◽  
Dynamic Mechanism ◽  
Gradient Force ◽  
Residual Water ◽  
Wet Season ◽  
The North

In a multilevel bifurcated estuary, the channels between the bifurcated branches play important roles in the exchanges of water and salt. In the Changjiang Estuary, the Hengsha Channel (HC) connects the North Channel (NC) and the North Passage (NP). In this paper, based on a two-way nesting unstructured quadrilateral grid, finite-differencing, three-dimensional estuarine and coastal ocean model, the tidal and seasonal variations in the water and salt transports in the HC were simulated, and their dynamic mechanism was analyzed. The residual water and salt transports in the HC both flow southward from the NC to the NP. In wet season, the residual water transport in the HC is 677 m3/s during neap tide and 245 m3/s during spring tide, and the residual salt transport is 0. In dry season, the residual water and salt transports in the HC are 1278 m3/s and 0.38 t/s during neap tide, respectively, and 1328 m3/s and 12.61 t/s during spring tide. Affected by the northerly wind and the southeastward baroclinic gradient force, the water and salt fluxes in dry season are much larger than those in wet season. The dynamic mechanism responsible for the water transport in the HC was numerically simulated and analyzed.

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