Salt intrusion in an estuarine network, a study with an exploratory model

2020 ◽  
Author(s):  
Huib E. de Swart ◽  
Inge van Tongeren
Keyword(s):  
River Water ◽  
Fresh Water ◽  
River Discharge ◽  
Yangtze Estuary ◽  
Strong Impact ◽  
The South ◽  
The Yangtze Estuary ◽  
Salt Intrusion ◽  
The North ◽  
Averaged Model

<p>Many estuarine systems experience increased salt intrusion, which is harmful for ecology and agriculture and may cause problems for fresh water supply to cities. Some causes of salt intrusion are extraction of fresh water in the upper reaches of the estuary and climate change. Besides, anthropogenic measures, like deepening of channels, are known to have a strong impact on the salt balance.</p><p>This contribution focuses on salt intrusion in estuarine networks, which consist of multiple connected channels. The motivation of the study arose from observations in the Yangtze estuary that reveal frequent overspill of salt between its different channels. To understand the underlying physics of such behaviour, an exploratory, width- and tidally averaged model has been developed and analysed. This model describes the competition between export of salt by river flow and import of salt by density-driven flow and horizontal diffusion. Its key new aspect is that it generalises an earlier model MacCready (2004) from a single channel to estuarine networks. The new model calculates the distribution of salt in, and salt exchange between the channels, as well as the distribution of river water over the different channels.  </p><p>Here, results will be presented for a simplified estuarine network consisting of the South Channel, South Passage and North Passage of the Yangtze Estuary. It will be shown that, for the present-day situation, dry season and spring tide, salt intrusion is larger in the South Passage than in the North Passage. As will be explained, this is mainly due to the different geometry of the two channels. Furthermore, it will be shown that there is slightly more river water transport through the South Passage than through the North Passage, except during high river discharge and neap tide. These results agree with field data and results from numerical studies.</p><p>Other results that will be presented are the sensitivity of salinity intrusion length and distribution of river water over the different channels to changes in, respectively, upstream river discharge, tidal currents and human interventions. Specifically, the effects of the creation of a Deepwater Navigation Channel in the North Passage on salt dynamics will be shown and discussed.</p><p>Reference:<br>MacCready, P. 2004. Toward a unified theory of tidally-averaged estuarine salinity structure. Estuaries 27, 561-570.</p>

scholarly journals THE BRANCHING CHANNEL NETWORK IN THE YANGTZE ESTUARY

2012 ◽  
Vol 1 (33) ◽  
pp. 69
Author(s):  
Zheng Bing Wang ◽  
Pingxing Ding
Keyword(s):  
Yangtze Estuary ◽  
River Delta ◽  
Sediment Supply ◽  
Channel Structure ◽  
The South ◽  
Channel Network ◽  
The Yangtze Estuary ◽  
The North ◽  
Navigation Channel ◽  
The Impact

The channels in the Yangtze Estuary have an ordered-branching structure: The estuary is first divided by the Chongming Island into the North Branch and the South Branch. Then the South Branch is divided into the North Channel and South Channel by the Islands Changxing and Hengsha. The South Channel is again divided into the North and South Passage by the Jiuduansha Shoal. This three-level bifurcation and four-outlet configuration appears to be a natural character of the estuary, also in the past (Chen et al., 1982), although the whole system has been extending into the East China Sea in the southeast direction due to the abundant sediment supply from the Yangtze River. Recently, the natural development of the system seems to be substantially disturbed by human interferences, especially the Deep Navigation Channel Project. For the understanding of the behaviour of the bifurcating channel system in the estuary we present analysis on two aspects: (1) the equilibrium configuration of river delta distributary networks, and (2) influence of tidal flow on the morphological equilibrium of rivers. Based on the analyses we conclude that the branching channel structure of the Yangtze Estuary can be classified as tide-influenced river delta distributary networks. Its basic structure is the same as in case of river dominated delta. The empirical relations describing the basic features of the river-dominated distributary delta networks can be explained by theoretical analysis, although they are not fully satisfied by the Yangtze Estuary because of the influence of the tide. Two major influences of the tide are identified, viz. increasing the resistance to the river flow into the sea and increasing the sediment transport capacity. As consequence of these two influences the cross-sectional area of the river/estuary increases in the seawards direction and the bed slope decreases. The insights from the analyses are helpful for the understanding of the impact of the Deep Navigation Channel Project on the large scale morphological development of the estuary.

Influences of River Discharge Variation and Tidal Asymmetry on the Spatial Evolution of the Turbidity Maximum Zone in Yangtze Estuary

2020 ◽  
Author(s):  
Ping Dong ◽  
Huabin Shi
Keyword(s):  
River Discharge ◽  
Yangtze Estuary ◽  
Turbidity Maximum ◽  
Tidal Range ◽  
Tidal Asymmetry ◽  
Interannual Variations ◽  
The South ◽  
Turbidity Maximum Zone ◽  
Averaged Model ◽  
Seasonal And Interannual Variations

<p>The Yangtze estuary is characterized by its extremely high suspended sediment concentration (SSC) and the extensive turbidity maximum zone (TMZ). The estuary is physically forced by an upstream river discharge seasonally varying in a wide range of 6000 – 92000 m3/s and semidiurnal-diurnal mixed tides with the tidal range up to 5 m. The influences of the seasonal and interannual variations in the upstream river discharge and the tidal asymmetry on the location of the Yangtze TMZ are numerically investigated with a two-dimensional depth-averaged model. Sensitivities of SSC and hence the location of TMZ to the bottom shear stress, bed erodibility, and the sediment settling velocity are studied. The spatial and temporal evolutions of the TMZ position in the cases of various upstream river discharges with different monthly, seasonal and interannual variations are simulated and discussed. The effects of the M2/M4-induce tidal asymmetry on the TMZ position and those of the interactions between the eight main astronomical tides (M2, S2, N2, K2, K1, O1, P1, and Q1) are compared. It is shown that the M2/M4-induce tidal asymmetry plays a critical role in the formulation of TMZ in the downstream of the South Branch of Yangtze estuary, while the interactions between the eight main astronomical tides have more significant effects on the TMZ location in other areas of Yangtze estuary such as the South and the North Passages.</p>

scholarly journals An analytical solution for tidal propagation in the Yangtze Estuary, China

2012 ◽  
Vol 16 (9) ◽  
pp. 3327-3339 ◽  
Author(s):  
E. F. Zhang ◽  
H. H. G. Savenije ◽  
S. L. Chen ◽  
X. H. Mao
Keyword(s):  
Analytical Solution ◽  
Analytical Model ◽  
Single Channel ◽  
Yangtze Estuary ◽  
The South ◽  
Tidal Dynamics ◽  
The Yangtze Estuary ◽  
The North ◽  
Tidal Propagation ◽  
First Time

Abstract. An analytical model for tidal dynamics has been applied to the Yangtze Estuary for the first time, to describe the tidal propagation in this large and typically branched estuary with three-order branches and four outlets to the sea. This study shows that the analytical model developed for a single-channel estuary can also accurately describe the tidal dynamics in a branched estuary, particularly in the downstream part. Within the same estuary system, the North Branch and the South Branches have a distinct tidal behaviour: the former being amplified demonstrating a marine character and the latter being damped with a riverine character. The satisfactory results for the South Channel and the South Branch using both separate and combined topographies confirm that the branched estuary system functions as an entity. To further test these results, it is suggested to collect more accurate and dense bathymetric and tidal information.

scholarly journals An analytical solution for tidal dynamics in the Yangtze Estuary, China

2012 ◽  
Vol 9 (2) ◽  
pp. 2213-2244 ◽  
Author(s):  
E. F. Zhang ◽  
H. H. G. Savenije ◽  
S. L. Chen ◽  
X. H. Mao
Keyword(s):  
Analytical Model ◽  
Single Channel ◽  
Yangtze Estuary ◽  
Phase Lag ◽  
The South ◽  
Tidal Dynamics ◽  
The Yangtze Estuary ◽  
Velocity Amplitude ◽  
The North ◽  
Wave Celerity

Abstract. An analytical model for tidal dynamics has been applied to the Yangtze Estuary, a large branched estuary with three-order branches and four outlets to the sea. This study shows that the analytical model developed for a single-channel estuary can also accurately describe the tidal dynamics in a branched estuary, particularly in the downstream part. For given geometry, friction, and tidal amplitude at the mouth of every branch, the tidal damping/amplification, the phase lag, the wave celerity, and the velocity amplitude along the estuary can be computed. Within the same estuary system, the North Branch and the South Branches have a distinct tidal behavior: the former being amplified demonstrating a marine character and the latter being damped with a riverine character. The satisfactory results for the South Channel and the South Branch using both separate and combined topographies confirm that the branched estuary system functions as an entity. To further test these results, it is suggested to collect more accurate and dense bathymetric and tidal information.

scholarly journals Study on the Spillover of Sediment during Typical Tidal Processes in the Yangtze Estuary Using a High-Resolution Numerical Model

2019 ◽  
Vol 7 (11) ◽  
pp. 390 ◽  
Author(s):  
Dechao Hu ◽  
Min Wang ◽  
Shiming Yao ◽  
Zhongwu Jin
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
Good Description ◽  
Sediment Concentration ◽  
Yangtze Estuary ◽  
Sediment Flux ◽  
The Yangtze Estuary ◽  
Cross Sectional ◽  
The North ◽  
The Difference

Because of special morphologies and complex runoff–tide interactions, the landward floodtide flows in Yangtze Estuary are observed to spill over from the North to the South Branches, carrying a lot of sediment. To quantitatively clarify the spillover problem, a two-dimensional numerical model using a high-resolution channel-refined unstructured grid is developed for the entire Yangtze Estuary from Datong to river mouths (620 km) and part of the East Sea. The developed model ensures a good description of the river-coast-ocean coupling, the irregular boundaries, and local river regimes in the Yangtze Estuary. In tests, the simulated histories of the tidal level, depth-averaged velocity, and sediment concentration agree well with field data. The spillover of sediment in the Yangtze Estuary is studied using the condition of a spring and a neap tide in dry seasons. For a representative cross-section in the upper reach of the North Branch (QLG), the difference of the cross-sectional sediment flux (CSSF) between floodtide and ebbtide durations is 43.85–11.26 × 104 t/day, accounting for 37.5–34.9% of the landward floodtide CSSF. The mechanics of sediment spillover in Yangtze Estuary are clarified in terms of a successive process comprising the source, transport, and drainage of the spillover sediment.

Simulating high ebb currents in the North Passage of the Yangtze estuary using a vertical 1-D model

2017 ◽  
Vol 196 ◽  
pp. 399-410 ◽  
Author(s):  
Yuyang Shao ◽  
Xiaoteng Shen ◽  
Jerome P.-Y. Maa ◽  
Jian Shen
Keyword(s):  
Yangtze Estuary ◽  
The Yangtze Estuary ◽  
The North ◽  
D Model

A NEW WATER-BUG FROM CANADA

1897 ◽  
Vol 29 (3) ◽  
pp. 56-56
Author(s):  
William H. Ashmead
Keyword(s):  
New Species ◽  
Fresh Water ◽  
North American ◽  
South American ◽  
The South ◽  
Water Stream ◽  
The North ◽  
Water Species

The interesting new species of water-bug described below was received some time ago from Abbé P. A. Bégin, of Sherbrooke, Canada. It was captured swimming on a fresh-water stream some little distance above Sherbrooke, and is of more than ordinary interest, from the fact that it belongs to the genus Halobatopsis, Bianchi, a genus not yet recognized in the North American fauna, and only recently characterized, being based upon the South American Halobates platensis, Berg., also a fresh-water species.

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