scholarly journals Recent Spatio-Temporal Variations of Suspended Sediment Concentrations in the Yangtze Estuary

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 818 ◽  
Author(s):  
Haifei Yang ◽  
Bochang Li ◽  
Chaoyang Zhang ◽  
Hongjie Qiao ◽  
Yuting Liu ◽  
...  
Keyword(s):  
Suspended Sediment ◽  
Sediment Concentration ◽  
Temporal Variations ◽  
Essential Elements ◽  
Yangtze Estuary ◽  
Sediment Flux ◽  
The Yangtze Estuary ◽  
Riverine Sediment ◽  
Mouth Bar ◽  
Outer Estuary

Water and sediment are two of the most essential elements in estuaries. Their product, suspended sediment concentration (SSC), is involved in hydrology, geomorphology and ecology. This study was focused on the spatial and temporal variations of SSC in the Yangtze Estuary under new situations after the closure of ~50,000 dams in the Yangtze basin, including the Three Gorges Dam (TGD) in 2003. It was found that the SSC first exhibited an increasing and then a decreasing trend longitudinally from Xuliujing Station to the outer estuary with the Turbidity Maximum Zone located in the mouth bar area. Vertically, the SSC in the bottom layers averaged 0.96 kg/m3, about 2.4 times larger than the surface layers (0.40 kg/m3). During spring tides, the SSCs were always higher than those in neap tides, which was fit for the cognition law. As for the seasonal variations in the North Branch and mouth bar area, the SSCs in the dry season were higher than those in the flood season, while in the upper reach of the South Branch and outer estuary, the seasonal variation of SSCs reversed. This phenomenon primarily reflected the competition of riverine sediment flux and local resuspended sediment flux by wind-induced waves. As for the interannual changes, the SSCs demonstrated overall fluctuant downward trends, determined by riverine sediment flux and influenced by waves. This study revealed the new situation of SSC and can be a reference for other related researches in the Yangtze Estuary.

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.

Analysis of tidal average saturated suspended sediment concentration of cohesive sediment in the Yangtze Estuary

2021 ◽  
Author(s):  
Junyu Tao ◽  
Peng Hu ◽  
Wei Li ◽  
Zhiguo He
Keyword(s):  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Cohesive Sediment ◽  
Yangtze Estuary ◽  
Shear Stresses ◽  
The Yangtze Estuary ◽  
Erosion And Deposition ◽  
Deposition Fluxes ◽  
The Impact

<p>It is generally believed that sediment erosion and deposition can’t occur simultaneously, which is also reflected in the classical Partheniades-Krone formulas used to calculate erosion and deposition flux. In this study, the erosion and deposition fluxes of cohesive sediment are integrated in the tidal period respectively, and when they are equal, the corresponding suspended cohesive sediment concentration is called ‘tidal average saturated concentration of cohesive sediment’. Theoretical analysis of the factors affecting the saturated concentration indicates that a large erosion coefficient results in a high saturated concentration level. The corresponding critical erosion and deposition shear stresses (i.e., τ<sub>e </sub>and τ<sub>d</sub>) at saturated concentration have many possibilities. Therefore, it is understandable that good agreement of suspended sediment concentration between simulation and observation have been obtained by adjusting τ<sub>e </sub>and τ<sub>d </sub>in the previous numerical simulation calibration. According to the relative magnitude of τ<sub>e </sub>and τ<sub>d</sub> at saturated concentration, the erosion and deposition fluxes of cohesive sediment can be divided into four situations: weak erosion (i.e., τ<sub>e  ></sub> τ<sub>d</sub>), intense erosion (i.e., τ<sub>e  <</sub> τ<sub>d</sub>), intense deposition (i.e., τ<sub>e  <</sub> τ<sub>d</sub>), and weak deposition (i.e., τ<sub>e > </sub>τ<sub>d</sub> ). A two-dimensional numerical model is applied to calculate the temporal and spatial variation of the saturated concentration of cohesive sediment in the Yangtze Estuary. Simulation results shows the following findings. 1) The impact of the fraction of the kth size class in the surface (top) layer of bed material on erosion flux of non-uniform cohesive sediment is necessary to be considered. Otherwise, the calculated saturated concentration of cohesive sediment is greater than the measured. 2) The differences between saturated concentration and the field calculated/measured suspended sediment concentration can be applied to infer bed erosion/deposition characteristics to some extent, and compared it with the measured erosion/deposition result, which in turn verifies the values of  τ<sub>e </sub>and τ<sub>d</sub> in the model. This finding provides insights for the following research on transport and diffusion of cohesive sediment in estuary and coastal areas.</p>

Retrieval and Analysis on the Sediment Concentration of the South Branch of the Yangtze Estuary Based on TM

2013 ◽  
Vol 353-356 ◽  
pp. 2763-2768 ◽  
Author(s):  
Jia Ling Hao ◽  
Tong Cao ◽  
Zhu Jun Zhang ◽  
Li Ping Yin
Keyword(s):  
Remote Sensing ◽  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Yangtze Estuary ◽  
The South ◽  
The Yangtze Estuary ◽  
Remote Sensing Technology ◽  
Sensing Technology ◽  
Quantitative Remote Sensing

Suspended sediment concentration is important index of water quality, and assessment coefficient of water environment. Remote sensing technology can overcome the shortcomings of conventional methods, such as low speed, long period, and scarce temporal and spatial data distribution. Thus it is meaningful to introduce remote sensing technology to monitoring suspended sediment. In this paper, two TM/ETM+ images of the Yangtze estuary were utilized, and based on review of available domestic and overseas remote sensing data of suspended sediment, also combined with analysis on the 21 samples of synchronizing collection on April 28, 2009 and 3 samples of synchronizing collection on March 26, 2000 at the same time of satellite passing through respectively, the inversion model of satellite quantitative data was setup correlated to suspended sediment concentration. Then the classification diagram of sediment concentration in the surface water at the South Branch of the Yangtze Estuary was drawn. This study gets the following conclusions:(1) TM4 band reflection coefficient is more related to surface sediment concentration, the correlation coefficient is 0.884. (2)Through the regression analysis, the quantitative remote sensing model is established. By the mode, using satellite picture, sediment concentration distribution map in study area is obtained. (3)The diffusion law of suspended sediment, the range of high turbid water region and the estuarine sediment transportation were further discussed from monitoring data, and its characteristic phenomenon were observed and the cause was also explained.

A Study of Turbulent Shear Stress on Fine-Grained Suspended Sediment Flocs Size in the Yangtze Estuary

2013 ◽  
Vol 353-356 ◽  
pp. 2720-2723 ◽  
Author(s):  
Jiang Cheng ◽  
Wei Pan ◽  
Pan Jun Du
Keyword(s):  
Shear Stress ◽  
Suspended Sediment ◽  
Sediment Concentration ◽  
High Energy ◽  
Yangtze Estuary ◽  
Turbulent Shear ◽  
The Yangtze Estuary ◽  
Fine Grained ◽  
Turbulent Shear Stress ◽  
Tidal Data

During the two surveys at both spring and neap tides in wet (July-August 2008) season, measurements of flow, turbulence, suspended sediment concentration (SSC), fine-grained sediment particle mean diameter (Dm) were carried out over 26 h that covered two M2 semidiurnal cycles in the middle north channel of the Yangtze estuary. The preliminary observations data show complex temporal and seasonal variation in estuarine flocculation of fine-grained sediment. In the high-turbidity and high-energy area of the Yangtze estuary, the flocculation processes indicate that the turbulence shear stress maybe the most important factor to the fine-grained sediment flocculation processes during the spring and neap tide cycle change. There exists a turning point of flocs Dm vs. turbulent shear stress. The neap tidal critical turbulent shear stress is around 0.1 Nm-2, much smaller that the spring tidal data of about 0.5 Nm-2.

Variation behavior of tidal dynamics in the Yangtze Estuary: implying the amplification of hydrodynamics and sediment dynamics by the human intervention

2020 ◽  
Author(s):  
Heqin Cheng ◽  
Wei Chen ◽  
Lizhi Teng ◽  
Xiaoting Yuan
Keyword(s):  
Seasonal Variation ◽  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Yangtze Estuary ◽  
Sediment Dynamics ◽  
Tidal Range ◽  
Tidal Dynamics ◽  
The Yangtze Estuary ◽  
Tidal Characteristic

<p><span><span>During the last decades, many estuarine systems in Europe (e.g. the Elbe, Ems, Loire) have shown increases in tidal range and in turbidity, which are linked to local human activity (i.e., deepening). Compared to these European estuaries, the Yangtze Estuary is much larger in scales, experiences much stronger river discharge, and it is subject to a strong seasonal variation in freshwater and sediment supply from the drainage area. Moreover, the Yangtze estuary is a complex network with several branches, connecting channels. The changes in the flow and sediment dynamics in the estuary may result from both local and nonlocal human activities. Despite the intense research efforts over the past two decades, it is still unclear which impact (local or nonlocal) is responsible for the changing flow and sediment characteristics in the estuary. Deep investigation of tidal characteristic quantities such as extreme tidal level, tidal range, amplitude of tidal constituents, tidal characteristic coefficient and suspended sediment concentration is performed in a systematic manner. It is accomplished using the extreme value analysis, the wavelet analysis and harmonic analysis of water level at 11 hydrography stations along the tidal river channel (Datong-Nanjing reach) and estuarine section (downstream the Xuliujing) during 2008-2016. Similar data analysis is also performed for the last four decades of 20th century and results are compared with the analysis of the recent measurements. The driving forces of the significant changes in tidal characteristic quantities and suspended sediment concentration are discussed. Results show that the tidal dynamics in the Yangtze estuary has been enhanced. Its seasonal variation is attributed to the adjustment of runoff distribution, which is mainly caused by the operation of Three Gorges Dam. In short-term, local changes of flow/sediment dynamics, terrain changes play a major role. In the long term (on the 40-year time scale), the effect of sea level rise on the increasing M2 constituent is obvious. This has mainly resulted from the enhancing anti-clockwise rotation of the synchronous tidal phase.</span></span></p><p> </p>

Sign in / Sign up

Export Citation Format

Share Document