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Wan Y.,Shanghai Estuarine and Coastal Science Research Center | Zhao D.,Shanghai Estuarine and Coastal Science Research Center
Environmental Monitoring and Assessment | Year: 2017

Spatial and temporal measurement data describing spring–neap variations of velocity, salinity, and suspended sediment concentration (SSC) in the North Passage Deepwater Navigational Channel (DNC) of the Yangtze Estuary, China, were obtained in the wet season of 2012. These data were collected in the middle of the DNC and apparently document the formation of a rather stable density stratification interface and salt wedge, especially during neap tides and slack waters. The convergent zone of residual currents, salinity transport, and sediment transport during neap and spring tides oscillates in the middle and lower reach of the DNC. It encourages the formation of a near-bed high-SSC layer, which favours siltation in the dredged channel. Both the near-bed gradient Richardson number and the bulk/layer Richardson number vary dramatically from around zero to several hundred from spring to neap tides. Stratification and turbulence damping effects near the estuarine turbidity maximum (ETM) area induce the upper half (near water surface) of the water body to be ebb-dominant and the lower part (near-bed) to be flood-dominant, which is a previously undocumented phenomenon in this region. These data reveal that the residual pattern of currents, salt flux and sediment flux are of critical differences in a stratified estuary, and that the salinity-induced baroclinic pressure gradient is a major factor controlling the vertical velocity structure. In addition, field observations indicate that the salinity and sediment transport of residuals generated by internal tidal asymmetry plays a dominant role in maintaining a stable density stratification interface near the estuarine front. © 2017, Springer International Publishing Switzerland.

Wu H.,Shanghai Estuarine and Coastal Science Research Center | Zhang J.,Yangtze Estuary Waterway Administration Bureau | Liu G.,Shanghai Estuarine and Coastal Science Research Center
Proceedings of the Coastal Engineering Conference | Year: 2010

Effects of estuary regulation engineering are related to structure type of its dykes, but it is difficult to study the effect of local complex structure with physical model directly. Taking N II C segment of the 2 nd phase project of Deep Water Channel at Yangtze Estuary as a case, the paper discussed the method of research on engineering effect of hollow block structure by combining flume experiment with physical model. The method makes it possible to research the effects on current and riverbed induced by complex local structure with large-scale physical model. By comparison of different schemes, it is derived that the scheme without 2600m-long training dike of NIIC segment do harm to the exit channel of North Passage, and there are little influence with the scheme of the height of 2600m-long training dike of NIIC segment debasing 1m or the scheme of adopting hollow-block mound breakwater structure.

Lan Y.-M.,Shanghai Ocean University | Guo W.-H.,Shanghai Estuarine and Coastal Science Research Center | Liu H.,Shanghai JiaoTong University | Song Q.-H.,Shanghai Ocean University | Yuan J.-T.,Shanghai Ocean University
Shuidonglixue Yanjiu yu Jinzhan/Chinese Journal of Hydrodynamics Ser. A | Year: 2010

An experimental study has been carried out to investigate impact pressures on a slab and a vertical pile due to regular waves. The pressures on the bottom of the slab are measured by pressure transducers and the hydrodynamic loads acting on the pile are measured by a four-component balance. The influences of relative clearance height and relative length of the slab on the impact pressures are discussed in detail. On the other hand, the hydrodynamic force exerting on the single pile is compared between the cases with and without the effect of the slab.

Liu G.,East China Normal University | Liu G.,Shanghai Estuarine and Coastal Science Research Center | Zhu J.,East China Normal University | Wang Y.,Shanghai Estuarine and Coastal Science Research Center | And 2 more authors.
Estuarine, Coastal and Shelf Science | Year: 2011

Four bottom-mounted instrument-equipped tripods were deployed at two sections spanning the region characterized by severe sedimentation rates in the Deepwater Navigation Channel (DNC) along the North Passage of Changjiang Estuary in order to observe currents, near-bed suspended sediment, and salinity. Seaward residual currents predominated in the up-estuary section. In contrast, a classical two-layered estuarine circulation pattern occurred in the down-estuary section. Flow moved seaward in the upper layer and a heavier inflow, driven by the salinity gradient, moved landward in the lower layer. The near-bed residual currents in the up-estuary section and the down-estuary section acted in opposing directions, which implies that the region is a convergence zone of near-bed residual currents that trap sediment at the bottom. The maximum salinity gradient at the maximum flood current indicates the presence of a strong front that induces sediment trapping and associated near-bottom convergence of sediment, which explains the high sedimentation rates in this section of the estuary. © 2010 Elsevier Ltd.

LIU G.-F.,Shanghai Estuarine and Coastal Science Research Center | WU J.-X.,Sun Yat Sen University | WANG Y.-Y.,Shanghai Estuarine and Coastal Science Research Center
International Journal of Sediment Research | Year: 2014

Numerous estuaries of the world have been strongly modified by human activities. These interferences can make great adjustments of not only sediment transport processes, but also the collective behavior of the estuary. This paper provides a typical case of a heavily modified coastal plain estuary of Sheyang on the China coast, where a sluice barrage was built in 1956 to stop the intrusions of storm surges and saline water. Four sets of instrumented tripods were simultaneously deployed along a cross-shore transect to continuously observe near-bed flow currents and sediment transport. The in-situ surveys lasted over a spring and neap tide cycle when a strong wind event occurred in the neap tide. Comparisons of flows and sediment transport between tide-dominated and wind-dominated conditions demonstrated the important role of episodic wind events in flows and sediment transport. The wind-induced currents, bottom stresses, and sediment transport rates were significantly greater when wind was present than corresponding quantities induced by the tides. The long-shore sediment transport induced by winds exceeds the cross-shore component, especially near the river mouth bar. These results indicate the noticeable importance of wave-dominated coastal processes in shaping topographic features. A regime shift of estuarine evolution under highly intense human forcing occurs from fluvial to marine processes. This finding suggests that the management strategy of the estuarine system should focus on the restoration of estuarine processes, rather than the present focus on inhibition of marine dynamics. © 2014 International Research and Training Centre on Erosion and Sedimentation and the World Association for Sedimentation and Erosion Research.

Jiang C.,East China Normal University | Jiang C.,University Utrecht | De Swart H.E.,University Utrecht | Li J.,East China Normal University | Liu G.,Shanghai Estuarine and Coastal Science Research Center
Ocean Dynamics | Year: 2013

The effects of large-scale interventions in the North Passage of the Yangtze Estuary (the Deep Waterway Project, DWP) on the along-channel flow structure, suspended sediment distribution and its transport along the main channel of this passage are investigated. The focus is explaining the changes in net sediment transport in terms of physical mechanisms. For this, data of flow and suspended sediment concentration (SSC), which were collected simultaneously at several locations and at different depths along the main channel of the North Passage prior to and after the engineering works, were harmonically analyzed to assess the relative importance of the transport components related to residual (time-mean) flow and various tidal pumping mechanisms. Expressions for main residual flow components were derived using theoretical principles. The SSC revealed that the estuarine turbidity maximum (ETM) was intensified due to the interventions, especially in wet seasons, and an upstream shift and extension of the ETM zone occurred. The amplitude of the M 2 tidal current considerably increased, and the residual flow structure was significantly altered by engineering works. Prior to the DWP, the residual flow structure was that of a gravitational circulation in both seasons, while after the DWP, there was seaward flow throughout the channel during the wet season. The analysis of net sediment transport reveals that during wet seasons and prior to the DWP, the sediment trapping was due to asymmetric tidal mixing, gravitational circulation, tidal rectification, and M 2 tidal pumping, while after the DWP, the trapping was primarily due to seaward transport caused by Stokes return flow and fresh water discharge and landward transport due to M 2 tidal pumping and asymmetric tidal mixing. During dry seasons, prior to the DWP, trapping of sediment at the bottom relied on landward transports due to Stokes transport, M 4 tidal pumping, asymmetric tidal mixing, and gravitational circulation, while after the DWP the sediment trapping was caused by M 2 tidal pumping, Stokes transport, asymmetric tidal mixing, tidal rectification, and gravitational circulation. © 2013 Springer-Verlag Berlin Heidelberg.

Wan Y.,Shanghai Estuarine and Coastal Science Research Center | Wan Y.,UNESCO-IHE Institute for Water Education | Gu F.,Shanghai Estuarine and Coastal Science Research Center | Wu H.,Shanghai Estuarine and Coastal Science Research Center | Roelvink D.,UNESCO-IHE Institute for Water Education
Applied Ocean Research | Year: 2014

Over the past decade, the Yangtze Estuary has witnessed an unprecedented scale of human interventions and modifications through extensively varied resource utilizations. During the processes, mankind has obtained various resources and benefits via the "golden waterway", such as navigation channel, harbor, shipping industry, shoreline, reclaimed land, freshwater and fishery resource. At the same time, the estuary and coast have also experienced a series of gradual changes in characteristics, such as sedimentation, erosion, sand hungry, water pollution, intertidal area loss, self-purification capacity decrease, and biological reduction. With the help of measurement data and numerical modeling, this study analyzed the response and feedback mechanisms between hydrodynamic evolutions and morphological processes in the Yangtze Estuary from 1998 to 2009. The results of this study indicate the following. (i) The water level along the main outlet of the Yangtze Estuary increased from 1998 to 2009. This increase was induced by the variation of the whole river regime (including natural geomorphodynamic process and local topography feedbacks from extreme metrological events and human activities). (ii) The decrease of the flow partition ratio at the 3rd bifurcation is directly induced by the Deepwater Navigational Channel (DNC) project and the corresponding morphological changes in the North Passage. (iii) The estuarine environmental gradients (salinity and suspended sediment concentration) were compressed, and the fresh-salt gradient became steeper. This has the indirect effect of backfilling in the waterway, i.e., strengthening the stratification effect near the ETM area and enhancing the tendency of up-estuary sediment transport. The results of this study give insights into explaining other phenomena such as deposition in the middle reach of the DNC, bathymetry evolutions, variations in vertical velocity and sediment concentration profiles, waterway backfilling and delta reclamation. © 2014 Elsevier Ltd.

Liu J.,Shanghai Estuarine and Coastal Science Research Center | Cheng H.,Shanghai Estuarine and Coastal Science Research Center | Zhao D.,Shanghai Estuarine and Coastal Science Research Center
Shuikexue Jinzhan/Advances in Water Science | Year: 2014

A series of dredging and hydrologic data in situ measurement are collected to study temporal-spatial variation characteristics of siltation, and the dependency relationship of siltation on riverine discharge, tidal range and local suspended sediment concentration in the 12.5 m Deepwater Navigational Channel (DNC) in the Yangtze Estuary.The results show that: (1) the quantity of siltation in DNC is much greater in flood season than that in dry season; (2) the sedimentation during storms is very serious; (3) the deposited sediments mainly distribute in the South Channel-Yuanyuansha Channel and the middle reach of the North Passage; (4) the grain size of the dredged sediment in the upper reach is greater than that in the lower reach; (5) the quantity of siltation in the South Channel-Yuanyuansha Channel is no sensitive to the riverine discharge, but it deposits more during spring-tide and less during neap-tide; (6) the central position of the siltation in the North Passage varies with the intensity of discharge, when the discharge becomes small, it move up-estuary, and vice versa; the quantity of siltation in the North Passage will get greater in flood season than in dry season; (7) the resuspension of the deposited sediments near the estuarine turbidity maxium area is the main contribution to the siltation in the dredged navigational channel.

Wan Y.,Shanghai Estuarine and Coastal Science Research Center | Wan Y.,UNESCO-IHE Institute for Water Education | Wu H.,Shanghai Estuarine and Coastal Science Research Center | Roelvink D.,UNESCO-IHE Institute for Water Education | Gu F.,Shanghai Estuarine and Coastal Science Research Center
Ocean Engineering | Year: 2015

Fall velocity (FV) is such a fundamental parameter for sediment researchers that its accurate determination has been regarded as a top priority in improving numerical modelling and conceptual understanding of fine sediment dynamics. With their cohesive nature, fine sediments are prone to aggregation and form flocculation network structures (flocs). The rheological behaviour of fluid may complicate this problem. By means of a new apparatus, FV of fine Yangtze Estuary sediment can be studied in the laboratory. The experimental data show that (1) suspended sediment concentration (SSC), salinity and temperature all affect FV, but to different extents; (2) the relationships between the FV of estuarine fine sediments and its determinants are highly dependent upon specific environmental conditions; (3) the dependencies of various determinants (SSC, salinity and temperature) on FV in different flocculation stages are varied; and (4) for Yangtze estuarine mud, the FV peaks when the SSC is in the range 3-8 g/l, and the salinities for maximum flocculation settling are approximately 7 and 10 PSU in dry and wet seasons, respectively. © 2015 Elsevier Ltd.

Wan Y.,Shanghai Estuarine and Coastal Science Research Center | Wan Y.,UNESCO-IHE Institute for Water Education | Roelvink D.,UNESCO-IHE Institute for Water Education | Li W.,Shanghai Estuarine and Coastal Science Research Center | And 2 more authors.
Geomorphology | Year: 2014

Observations of storm-induced fluid mud dynamics have been conducted at the North Passage deepwater navigational channel (DNC) of the Yangtze Estuary in October to December 2010, during the occurrence of a cold-air front. The measurement data reveal that just after the critical wind wave event, a large amount of fine sediment was trapped in a state of fluid mud along the channel. The observed thickness of the fluid mud was up to about 1-5. m, which caused some significant economic and safety problems for shipping traffic in the Yangtze Delta area. The mechanisms and transport processes of the storm-induced fluid mud are analyzed and presented from the angles of both process-oriented and engineering-oriented methods. With the help of hydrodynamics and wave modeling, it could be inferred that the behavior of the storm-induced fluid mud event mainly depends on the overall hydrodynamic regimes and the exchanges of sediment, which is released by storm-wave agitation from adjacent tidal flats. These sediments are accumulated as fluid mud, and subsequently oscillate and persist at those locations with weaker longitudinal residuals in the river- and tide-dominated estuary. In addition, the downslope transport of fluid mud is also thought to have stimulated and worsened the fluid mud event observed in this study. Our modeling results and observations demonstrate that: (1) the transport of fluid mud is an advective phenomenon determining the central position of fluid mud layer along the channel, and it's also a tidal energy influenced phenomenon controlling the erosion and accumulation of fluid mud; and (2) both suspended particulate matter availability and local residual flow regime are of critical importance in determining the trapping probability of sediment and the occurrence of fluid mud. © 2013 Elsevier B.V.

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