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.

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>

Observations of Nepheloid Layers in the Yangtze Estuary, China, Through Phase-Corrupted Acoustic Doppler Current Profiler Speeds

2012 ◽  
Vol 46 (4) ◽  
pp. 60-70 ◽  
Author(s):  
Zhenyi Cao ◽  
Xiao Hua Wang ◽  
Weibing Guan ◽  
Les J. Hamilton ◽  
Qi Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Acoustic Doppler Current Profiler ◽  
Yangtze Estuary ◽  
Fluid Mud ◽  
Nepheloid Layer ◽  
The Yangtze Estuary ◽  
Mean Velocity ◽  
The North ◽  
Navigation Channel ◽  
Current Profiler

AbstractA bottom quadrapod was deployed from March 29 to April 5, 2009 to measure bottom boundary layer (BBL) flows and nepheloid layer properties in the Deepwater Navigation Channel in the North Passage of Shanghai Port in the Yangtze estuary. Using a downward-looking acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimeter, detailed measurements of mean velocity and turbulence distribution within 1 m above the seabed were obtained. It appears that corrupted speeds measured for the deeper bins are caused by formation of the nepheloid layer at the seabed, implying that the ADCP is not a suitable instrument to measure current velocities in the bins nearest the seafloor. A statistical clustering method was used to characterize the current profiles in the BBL. The majority of current profiles within the BBL had a simple shape with current speed monotonically decreasing with depth, reflecting a logarithmic boundary layer. Phase-corrupted ADCP speeds measured for bins close to the bottom are shown to be useful as proxies to indicate the presence of primary and secondary lutoclines/nepheloid layers. A lutocline is a sediment-induced density gradient or pycnocline. The primary lutocline is closest to the bottom, and below it is the nepheloid layer, which is commonly composed of fluid mud. The proxies indicated that a nepheloid layer formed in the neap tide when the current velocity 1 m above the seabed dropped below a threshold of 0.65 m/s. The lutocline height was indicated to be about 0.2 m above the seabed. A secondary lutocline in the water column was also observed in the second half of the record, when the lowest maximum currents occurred.

scholarly journals SEDIMENTOLOGY AND SEQUENCE STRATIGRAPHY OF SHALLOW MARINE SEDIMENTS IN A SYN-RIFT SETTING: HUGIN FORMATION, SOUTH VIKING GRABEN

2018 ◽  
Author(s):  
Rachel Kieft ◽  
Christopher Aiden-Lee Jackson ◽  
Gary J. Hampson
Keyword(s):  
Sequence Stratigraphy ◽  
Structural Features ◽  
Sediment Supply ◽  
Structural Development ◽  
The South ◽  
Candidate Sequence ◽  
Shallow Marine ◽  
The North ◽  
Facies Associations ◽  
The Impact

Fault growth and linkage within rift basins generates localised uplift and subsidence, which may exert significant control over syn-rift sedimentation. The shallow-marine Hugin Formation within the South Viking Graben, a salt-influenced rift basin, is studied as an example of such sedimentation. The principal aims of this thesis are to: (1) characterise the sedimentology and sequence stratigraphy of the succession, (2) investigate structural development within the graben by analysis of the hangingwall dipslope, and (3) establish the impact of syn-depositional structural development on shallow marine sedimentation. Sedimentological analysis of the Hugin Formation has recognised fifteen facies that are grouped into six facies associations: bay-fill, shoreface, fluvio-tidal channel fill, mouth bar, coastal plain and offshore open marine. Combining the results of this analysis with biostratigraphy, the studied succession is subdivided into a series of units delineated by regionally correlatable maximum flooding surfaces. Within the stratigraphic framework delineated by these surfaces each of the main facies associations are developed coevally in distinct and different geographical locations. Higher order flooding surfaces, transgressive surfaces and candidate sequence boundaries can also be interpreted within this framework which are geographically localised. Structural analysis of the hangingwall dipslope identified a series of distinct structural features that were evolving contemporaneous with Hugin Formation deposition. To the north, the gravity-driven Gudrun-Brynhild fault array initiated as a series of distinct segments which subsequently propagated and linked. Further south, the salt-cored highs at Dagny and Alpha Central were also developing. Palaeogeographical localisation of facies associations is interpreted to reflect deposition within these different structural locations along with proximity to the axial fluvial feeder system to the south of the basin. Sediment supply via wave-driven longshore drift from the north of the basin and local re-working of structurally controlled palaeohighs was also important.

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.

Nachhaltigkeit im Wald – vor und hinter der Welle der Globalisierung | Sustainable Forest Management – In Front and Behind the Wave of Globalization

2000 ◽  
Vol 151 (12) ◽  
pp. 502-507
Author(s):  
Christian Küchli
Keyword(s):  
Forest Management ◽  
Cultural Landscape ◽  
Sustainable Forest Management ◽  
Essential Element ◽  
Specific Situation ◽  
The South ◽  
The North ◽  
Time Space ◽  
Starting Point ◽  
The Impact

Are there any common patterns in the transition processes from traditional and more or less sustainable forest management to exploitative use, which can regularly be observed both in central Europe and in the countries of the South (e.g. India or Indonesia)? Attempts were made with a time-space-model to typify those force fields, in which traditional sustainable forest management is undermined and is then transformed into a modern type of sustainable forest management. Although it is unlikely that the history of the North will become the future of the South, the glimpse into the northern past offers a useful starting point for the understanding of the current situation in the South, which in turn could stimulate the debate on development. For instance, the patterns which stand behind the conflicts on forest use in the Himalayas are very similar to the conflicts in the Alps. In the same way, the impact of socio-economic changes on the environment – key word ‹globalisation› – is often much the same. To recognize comparable patterns can be very valuable because it can act as a stimulant for the search of political, legal and technical solutions adapted to a specific situation. For the global community the realization of the way political-economic alliances work at the head of the ‹globalisationwave›can only signify to carry on trying to find a common language and understanding at the negotiation tables. On the lee side of the destructive breaker it is necessary to conserve and care for what survived. As it was the case in Switzerland these forest islands could once become the germination points for the genesis of a cultural landscape, where close-to-nature managed forests will constitute an essential element.

scholarly journals Assessing the Sensitivity of Main Crop Yields to Climate Change Impacts in China

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 172
Author(s):  
Yuan Xu ◽  
Jieming Chou ◽  
Fan Yang ◽  
Mingyang Sun ◽  
Weixing Zhao ◽  
...  
Keyword(s):  
Climate Change ◽  
Crop Yield ◽  
Food Production ◽  
Crop Yields ◽  
Climatic Factors ◽  
Climatic Data ◽  
The South ◽  
The North ◽  
Output Elasticity ◽  
The Impact

Quantitatively assessing the spatial divergence of the sensitivity of crop yield to climate change is of great significance for reducing the climate change risk to food production. We use socio-economic and climatic data from 1981 to 2015 to examine how climate variability led to variation in yield, as simulated by an economy–climate model (C-D-C). The sensitivity of crop yield to the impact of climate change refers to the change in yield caused by changing climatic factors under the condition of constant non-climatic factors. An ‘output elasticity of comprehensive climate factor (CCF)’ approach determines the sensitivity, using the yields per hectare for grain, rice, wheat and maize in China’s main grain-producing areas as a case study. The results show that the CCF has a negative trend at a rate of −0.84/(10a) in the North region, while a positive trend of 0.79/(10a) is observed for the South region. Climate change promotes the ensemble increase in yields, and the contribution of agricultural labor force and total mechanical power to yields are greater, indicating that the yield in major grain-producing areas mainly depends on labor resources and the level of mechanization. However, the sensitivities to climate change of different crop yields to climate change present obvious regional differences: the sensitivity to climate change of the yield per hectare for maize in the North region was stronger than that in the South region. Therefore, the increase in the yield per hectare for maize in the North region due to the positive impacts of climate change was greater than that in the South region. In contrast, the sensitivity to climate change of the yield per hectare for rice in the South region was stronger than that in the North region. Furthermore, the sensitivity to climate change of maize per hectare yield was stronger than that of rice and wheat in the North region, and that of rice was the highest of the three crop yields in the South region. Finally, the economy–climate sensitivity zones of different crops were determined by the output elasticity of the CCF to help adapt to climate change and prevent food production risks.

scholarly journals A tale of two parts of Switzerland: regional differences in the impact of the COVID-19 pandemic on parents

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Michelle Seiler ◽  
Georg Staubli ◽  
Julia Hoeffe ◽  
Gianluca Gualco ◽  
Sergio Manzano ◽  
...  
Keyword(s):  
Public Health ◽  
Regional Differences ◽  
Online Survey ◽  
Pediatric Emergency ◽  
The South ◽  
Public Health Agencies ◽  
The North ◽  
Regional Strategies ◽  
Health Agencies ◽  
The Impact

Abstract Background We aimed to document the impact of the coronavirus disease 2019 (COVID-19) pandemic on regions within a European country. Methods Parents arriving at two pediatric emergency departments (EDs) in North of Switzerland and two in South of Switzerland completed an online survey during the first peak of the pandemic (April–June 2020). They were asked to rate their concern about their children or themselves having COVID-19. Results A total of 662 respondents completed the survey. Parents in the South were significantly more exposed to someone tested positive for COVID-19 than in the North (13.9 and 4.7%, respectively; P <  0.001). Parents in the South were much more concerned than in the North that they (mean 4.61 and 3.32, respectively; P <  0.001) or their child (mean 4.79 and 3.17, respectively; P <  0.001) had COVID-19. Parents reported their children wore facemasks significantly more often in the South than in the North (71.5 and 23.5%, respectively; P <  0.001). Conclusion The COVID-19 pandemic resulted in significant regional differences among families arriving at EDs in Switzerland. Public health agencies should consider regional strategies, rather than country-wide guidelines, in future pandemics and for vaccination against COVID-19 for children.

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