Mechanisms of along-channel sediment transport in the North Passage of the Yangtze Estuary and their response to large-scale interventions Topical Collection on the 11th International Conference on Cohesive Sediment Transport
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.
Zhang Z.,Survey Bureau of the Hydrology |
Li X.,Shanghai Maritime University |
Wang Y.,Shanghai Estuarine and Coastal Science Research Center
Proceedings of the 5th International Conference on Asian and Pacific Coasts, APAC 2009 | Year: 2010
Nowadays, ADCP is commonly applied in the measurement of river flow discharge and flow field. The Doppler shift between the emitting and receiving signals of acoustic is the major methodology of the application in measurement. Since the suspended particles in river are the main objects that cause the acoustic backscattering, the ADCP Acoustic Backscatter (ABS) can be converted to Suspended Sediment Concentration (SSC) using the sonar equation, and the synchronous profile of flow velocity and sediment concentration can be obtained. After the 10 m deep Navigable Channel in the Yangtze Estuary was opened in March 2005. The actually annual amount of maintenance has being risen every year. In the early study phase, it was found that the original operation of dredging and dumping sediment is not effective. In order to understand the effects of the application of the optimized operation method, the synchronous measurements of sediment spread region were carried out while dumping the dredged sediment in the No. 10 Dump Area in the North Passage of the Yangtze Estuary during the tidal fluctuation by 6 ADCP hydrologic survey boats in September 2008. It is concluded that the spread impact of dump sediment is related to the flow velocity; when the velocity is about 1.35 m/s. The sediment spread region presents a narrow strip with greater than 1 km long, but only following the flow, with minor deposit impact on the navigation channel. © 2010 World Scientific Publishing Co. Pte. Ltd.
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.
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.