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Abstract: Sediment transport in suspension can represent more than 90% of a river's total annual flux of sediment. In the case of the Yangtze River, more than 99% of the sediment supplied to the sea is suspended load. Suspended sediment is thus an important component of the total sediment load, with implications for channel dynamics, landscape evolution, ecology, and human‐related activities. For hydrological management of large basins such as the Yangtze River, knowledge of the processes governing suspended sediment concentration (SSC) is essential. An analysis of the temporal variation of SSC for the Upper Yangtze basin (defined at Pingshan station) is presented here. For this purpose, a database of 50 years of concurrent discharge and SSC measurements, made by the Yangtze River Commission, is used. The analysis is made using a novel probabilistic data‐driven technique, the Generalized Pareto Uncertainty (GPU). This technique allows for the testing of several strategies of prediction and forecast applied to a time series of SSC and streamflow. Changing between local or seasonal variables to feed these strategies, we inferred that although the main driver of the SSC transport is flow (as reported by previous authors), sediment storage is also a major control. Furthermore, the maximum necessary time lag for forecasts made with the data is on the order of one week, which provides one indication of the time scale of the local processes of SSC transport in the Upper Yangtze. In this paper, limitations and data requirements of the GPU methodology are also discussed. [ABSTRACT FROM AUTHOR]

This paper examines the morphological development of the Yangtze River mouth, which has been diverting southeasterly (dextrally), according to historical (150 years) chart-based digital evolution model and on-site measured tidal flow data. We reveal a significantly narrowing of the northern river mouth branch from formerly >30 km wide to presently 10 km wide due to rapid siltation. Net siltation there, however, decreases gradually, which largely contrasts with the fact that the siltation has shifted to the southern river mouth area, as shown by many newly-emerged estuarine islands, sandy shoals and bifurcated branches. Our data have further demonstrated that the ebb flow that dominates in the study area changes its direction gradually from east to southeast from the inner to outer river mouth area, and its duration is much longer than the flood flow in the inner river mouth area, but nearly equal at the river mouth area. Accordingly, the sediment transport pathway has been diverted from east to southeast. We examine whether the Coriolis Force could explain the dextral diversion of the ebb flow and the altered morphodynamical processes. Although too weak to strengthen the tidal flows, the Coriolis Force can drag the ebb flow southeasterly, and so influence sediment transport paths at the estuarine scale. The Coriolis Force is limited in the inner river mouth, but substantial at and in the outer river mouth area when gradually free of estuarine topographic constraints. The Coriolis Force causes an offset in propagation of in-out flow directions at the river mouth area to form a slack water setting prone to estuarine siltation. Using the present approach also enables explanation of the morphological development of the Holocene Yangtze delta-coast that extends to the southeast. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lateral flow significantly contributes to the near‐bottom mass transport of salinity in a channel‐shoal system. In this study, an integrated tripod system was deployed in the transition zone of a channel‐shoal system of the Changjiang Estuary (CE), China, to observe the near‐bottom physics with high temporal/spatial resolution, particularly focusing on the lateral‐flow‐induced mass transport. These in situ observations revealed a small‐scale salinity fluctuation around low water slack during moderate and spring tidal conditions. A simultaneous strong lateral current was also observed, which was responsible for this small‐scale fluctuation. A high‐resolution unstructured‐grid Finite‐Volume Community Ocean Model has been applied for the CE to better understand the mechanism of this lateral flow and its impact on salinity transport. The model results indicate that a significant southward near‐bed shoal‐to‐channel current is generated by the salinity‐driven baroclinic pressure gradient. This lateral current affects the salinity transport pattern and the residual current in the cross‐channel direction. Cross‐channel residual current shows a two‐layer structure in the vertical, especially in the intermediate tide when the lateral flow notably occurred. Both observation and model results indicate that near‐bottom residual transport of water moved consistently southward (shoal to channel). Mechanisms for this intratidal salinity variation and its implications can be extended to other estuaries with similar channel‐shoal features. Plain Language Summary: In channel‐shoal systems, lateral processes sometimes can be of great significance, for example, influencing salinity and sediment transport, even some biogeochemical matters that influence the water environment. Salinity and sediment transport will have a further effect on navigability, ecology, and so on, for example, sediment deposition issues, which significantly decrease the shipping capacity. Consequently, knowing the accurate information about the flow field and finding a criterion for pronounced lateral processes are important to better understand hydrodynamics and sediment behaviors in channel‐shoal systems. Here in this study, we conducted an in situ observation and used numerical simulation to detect and predict a strong lateral flow in the North Passage of the Changjiang Estuary. This shoal‐to‐channel lateral flow occurred around the end of ebb and caused an intratidal salinity variation at the observation site, close to the deep channel. Therefore, a link between pronounced lateral flows and typical salinity variation can be established. This link can also be found in other estuaries like Hudson River estuary. Findings presented here will help to easily distinguish pronounced lateral flows and better understand the effect of lateral flows. Key Points: Intratidal salinity variation (ISV) and a strong lateral flow in a channel‐shoal system were identified by an integrated tripod systemNumerical simulation reveals that lateral flows were primarily driven by the salinity‐induced pressure gradient forceLateral flows can be generated or enhanced by human interventions such as groyne fields [ABSTRACT FROM AUTHOR]

The sediment saturation recovery process (i.e. the adaptation of suspended sediment concentration [SSC] to local forcing) is the main feature of the non-equilibrium suspended sediment transport (SST) frequently occurring in fluvial, estuarine and coastal waters. In order to quantitatively describe this phenomenon, a series solution is analytically derived, including the evolution of both vertical SSC profile and near-bed sediment flux (NBSF), and is verified by net erosion and net deposition experiments, respectively. The results suggest that the sediment saturation recovery process involves vertically varying fluxes that are not represented correctly by depth-averaging. Consequently, a vertical two-dimensional (2D) combined scheme is established and applied respectively in to a dredged trench and to a sand wave feature to demonstrate this argument. By analyzing the variations of the calculated depth-averaged SSC and NBSF we reveal that the equilibrium state presented by the sediment carrying capacity (SCC) form of the NBSF, which is usually applied in depth-integrated SST models, lags behind the actual dynamic bed equilibrium state. Moreover, the key factor α, the so-called saturation recovery coefficient within this form, is not only a function of local Rouse number but also is influenced by the local SSC profile. Finally, a three-dimensional (3D) non-orthogonal curvilinear body-fitted SST model is developed and validated in the Yangtze estuary, China, combined with the in situ hourly hydrographic data from August 14-15, 2007 during spring tide in the wet season. Model results confirm that the vertically varying sediment saturation recovery process, the discrepancies between the actual and SCC form of NBSF and non-constant value of α are significant in actual real geomorphic cases. The quantitative morphological change resulting from variations in environmental conditions may not be correctly represented by uncorrected depth-integrated SST models if they do not treat the effects of vertical motion on the sediment saturation recovery process. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using the finite volume method, a 2-D water-sediment coupled model was developed to investigate the transport mechanisms of water and sediment in Poyang Lake, the largest river-connected lake in China. Simulating water and sediment transport processes in an average water year revealed that the total volume of water and the amount of suspended sediment transported from the five main rivers upstream of Poyang Lake were approximately 1.56 × 1011 m3 and 1.25 × 107 t, respectively. The outputs of water and sediment from the lake to the downstream Yangtze River were approximately 2.17 × 1011 m3 and 1.53 × 107 t, respectively. During the wet season, especially between July and September, nearly 1.06 × 1010 m3 of water and 1.89 × 106 t of suspended sediment were transported upstream from the Yangtze River into the lake due to the high external water levels, which accounted for 4.88% and 12.35%, respectively, of the total annual transport from the lake into the Yangtze River. [ABSTRACT FROM AUTHOR]