scholarly journals Seasonal Estuarine Turbidity Maximum under Strong Tidal Dynamics: Three-Year Observations in the Changjiang River Estuary

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1854
Author(s):  
Xia Hua ◽  
Huiming Huang ◽  
Yigang Wang ◽  
Xiao Yu ◽  
Kun Zhao ◽  
...  
Keyword(s):  
Sediment Transport ◽  
River Discharge ◽  
River Estuary ◽  
Changjiang River ◽  
Changjiang River Estuary ◽  
Wet Season ◽  
Tidal Dynamics ◽  
The Changjiang River ◽  
The Changjiang River Estuary ◽  
Dry Seasons

The estuarine turbidity maximum (ETM) under strong tidal dynamics (during spring tides) was investigated along the Deepwater Navigation Channel (DNC) in the North Passage (NP) of the Changjiang River Estuary (CRE) in wet and dry seasons of 2016, 2017 and 2018. The observed water current, salinity, stratification and suspended sediment concentration (SSC) were illustrated and analyzed. Results show that the SSC was lower in wet seasons than dry seasons in 2016 and 2017 because of the weak influence of typhoons before observations in wet seasons. On the contrary, the SSC was higher in the wet season than the dry season in 2018 because of the strong influence of typhoons in the wet season. Our observations challenged the common perspective that SSC in the NP is higher in wet seasons than dry seasons, because the magnitudes of SSC were found to be easily influenced by strong winds before observations. The along-channel distribution of high SSC was determined by the location of salt wedge, and consequently, the ETM was further upstream in dry seasons than wet seasons. The observed SSC was more concentrated in lower water layers in wet seasons (“exponential” profile) than dry seasons (“linear” profile). This seasonal difference of vertical SSC was related to the flocculation setting velocity influenced by temperature rather than the weak stratification during spring tides. Moreover, on the basis of the net water/sediment transport and flux splitting, large river discharge and a low-SSC condition could reduce siltation in the middle DNC. The former vanished the convergence of water transport, and the latter reduced landward tidal pumping sediment transport. Sediment trapping and siltation in the dry seasons occurred in the seaward segment of the upper reach because of the decrease in the river discharge.

Simulation to Investigate the Reasons for the Sediment Deposition in the Upper Reach of the Deepwater Navigation Channel in the Changjiang River Estuary

2012 ◽  
Vol 610-613 ◽  
pp. 1237-1241
Author(s):  
Jie Gu ◽  
Wei Chen ◽  
Xin Qin ◽  
Dan Qing Ma ◽  
Xiao Li Wang ◽  
...  
Keyword(s):  
River Estuary ◽  
Sediment Deposition ◽  
Changjiang River ◽  
Changjiang River Estuary ◽  
The Changjiang River ◽  
The North ◽  
Velocity Magnitude ◽  
Navigation Channel ◽  
The Changjiang River Estuary ◽  
Set Up

At present, the upper reach of the Deepwater Navigation Channel is silted heavily, which brings negative influences on navigation. A two-dimensional numerical model is set up to simulate the hydrodynamics of the Changjiang River Estuary with Delft3D-FLOW in this paper. This model has been validated with the observed tidal level, flow velocity magnitude and direction, and the computed results agree well with the observed data, which also shows the model can well simulate the hydrodynamics of the Changjiang River Estuary caused by the Deepwater Navigation Channel Project. Based on the analysis of computed results, especially the velocity along the South Passage and North Passage, the flood and ebb flow in the Hengsha Passage, and the flow spilt ratio of South Passage and North Passage, it presents that one fundamental reason for the sediment deposition in the upper reach of the Deepwater Navigation Channel is that the velocity along the North Passage is far less than that along South Passage, above all, the velocity in North Passage upstream of the Hengsha Passage is even smaller; another reason is that the flood and ebb flow of Hengsha Passage are large, which weakens the water exchange between the North Passage and South Channel.

scholarly journals Assessment of Extreme Storm Surges over the Changjiang River Estuary from a Wave–Current Coupled Model

2021 ◽  
Vol 9 (11) ◽  
pp. 1222
Author(s):  
Yutao Chi ◽  
Zengrui Rong
Keyword(s):  
Return Period ◽  
River Estuary ◽  
Coupled Model ◽  
Storm Surges ◽  
Distribution Model ◽  
Changjiang River ◽  
Changjiang River Estuary ◽  
The Changjiang River ◽  
The Changjiang River Estuary ◽  
The Impact

Disastrous storm surges and waves caused by typhoons are major marine dynamic disasters affecting the east China coast and the Changjiang River Estuary, especially when they occur coincidentally. In this study, a high-resolution wave–current coupled model consisting of ADCIRC (Advanced Circulation) and SWAN (Simulating Waves Nearshore) was established and validated. The model shows reasonable skills in reproducing the surge levels and waves. The storm surges and associated waves are then simulated for 98 typhoons affecting the Changjiang River Estuary over the past 32 years (1987–2018). Two different wind fields, the ERA reanalysis and the ERA-based synthetic wind with a theoretical typhoon model, were adopted to discern the potential uncertainties associated with winds. Model results forced by the ERA reanalysis show comparative skills with the synthetic winds, but differences may be relatively large in specific stations. The extreme surge levels with a 50-year return period are then presented based on the coupled model results and the Gumbel distribution model. Higher risk is presented in Hangzhou Bay and the nearshore region along the coast of Zhejiang. Comparative runs with and without wave effects were conducted to discern the impact of waves on the extreme surge levels. The wave setup contributes to 2–12.5% of the 50-year extreme surge level. Furthermore, the joint exceedance probabilities of high surge levels and high wave height were evaluated with the Gumbel–logistic statistic model. Given the same joint return period, the nearshore region along the coast of Zhejiang is more vulnerable with high surges and large waves than the Changjiang River Estuary with large waves and moderate surges.

scholarly journals Effects of the interaction of ocean acidification, solar radiation, and warming on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary

2017 ◽  
Author(s):  
Shan Jian ◽  
Jing Zhang ◽  
Hong-Hai Zhang ◽  
Gui-Peng Yang
Keyword(s):  
Solar Radiation ◽  
Ocean Acidification ◽  
River Estuary ◽  
Sulfur Compounds ◽  
Changjiang River ◽  
Changjiang River Estuary ◽  
Chl A ◽  
The Changjiang River ◽  
Temperature Conditions ◽  
The Changjiang River Estuary

Abstract. Ocean acidification (OA) affects marine primary productivity and community structure, and therefore may influence the biogeochemical cycles of volatile biogenic dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) and photochemical oxidation product dimethyl sulfoxide (DMSO). A 23-day incubation experiment on board was conducted to investigate the short-term response of biogenic sulfur compounds production and cycling to OA in the Changjiang River Estuary and further understand its effects on biogenic sulfur compounds. Result showed that phytoplankton abundance and species presented remarkable differences under three different pH levels in the late stage of the experiment. A significant reduction in chlorophyll a (Chl-a), DMS, particulate DMSP (DMSPp), and dissolved DMSO (DMSOd) concentrations was identified under high CO2 levels. Moreover, minimal change was observed in the production of dissolved DMSP (DMSPd) and particulate DMSO (DMSOp) among treatments. The ratios of DMS, total DMSP (DMSPt), and total DMSO (DMSOt) to Chl-a were also not affected by a change in pH. In addition, DMS and DMSOd were highly related to mean bacterial abundance under three pH levels. Additional incubation experiments on light and temperature showed that the influence of pH on productions of dimethylated sulfur compounds also depended on solar radiation and temperature conditions. DMS photodegradation rate increased with decreasing pH under full-spectrum natural light and UVB light. Thus, OA may lead to decreasing DMS concentrations in the surface seawater. Light and temperature conditions also play an important role in the production and cycling of biogenic sulfur compounds.

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