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Abstract: The 165 year morphological evolution of the Changjiang (Yangtze) Estuary and its long-term equilibrium characteristics have been investigated using 16 selected maritime charts from 1842 to 2006. These charts were digitized and analyzed with a GIS to provide quantitative estimates of geomorphologic changes below selected bottom elevations. The results show that the Changjiang Estuary has experienced overall erosion over this 165 year period, having been affected by several large erosion and deposition episodes. It is found that the overall volume changes are less than 10% and aspect ratios of <5 have increased from 2% to ca. 30%. During this period, both coastlines and thalwegs have become straighter and more aligned with the propagation direction of offshore tidal current, indicating that the estuary is approaching dynamic equilibrium. Based on variations of aspect ratios and thalweg movements, five types of stable channels were identified. Significant topographical changes, including infilling after 1958 and erosion after 1980, are principally associated with engineering work around the estuary and a reduction in sediment supply. Although human influence only notably occurred at certain locations in the estuary, such as upstream node of an estuary, it had a significant impact on the overall geomorphologic evolution. In addition to these anthropogenic effects, freshwater flow, sediment discharges, tide propagation and Coriolis force are also found to play important roles in channel development within the estuary. By contrast, changes in other factors such as sea level changes and wave climate were considered to be of relatively minor importance in the morphological evolution process of the estuary. [Copyright &y& Elsevier]

Abstract: Provenance discrimination of marine sediments is an important topic in marine geology. Although the catchments of the Changjiang and Huanghe Rivers are regarded as the main sources of sediments on the shelves of the China Sea, identification of detailed sediment provenance is necessary for understanding sediment transport patterns and the paleoenvironment. Magnetic properties of both bulk sediment samples and different-sized particles from the Changjiang and Huanghe Estuaries are studied to discuss the origin of the sediments. The results show that the sediments are dominated by ferrimagnetic magnetite with a minor content of anti-ferromagnetic minerals such as hematite, and a higher concentration of ferrimagnetic minerals is observed for the Changjiang Estuary sediments. The crystal grains of ferrimagnetic minerals in the Changjiang Estuary are coarser than those in the Huanghe Estuary, whereas superparamagnetic grains significantly contribute to the Huanghe sediments. Magnetic parameters of χ SIRM, SOFT and χ ARM from different-sized particles present more obvious differences than these parameters from bulk particles, and S−100 and S−300 for both bulk samples and different-sized particles show distinct differences between the sediments from the two estuaries. Therefore the latter parameters are more useful to distinguish sediment origins. A comparison of the magnetic properties of sediments in these two estuaries with those on the shelves of the adjacent China Sea also suggests that the analysis of sediment magnetic properties is effective to identify sediment provenances. [Copyright &y& Elsevier]

Abstract: Bed features were mapped using a thermal depth recorder and a side-scan sonar in the Changjiang (Yangtze) Estuary, and flows were observed and bed surface materials were sampled to investigate bed material transport pathways. Distinct scales and dimensions of dunes were observed in terms of the classification scheme of Ashley [Ashley, G.M., 1990. Classification of large-scale sub-aqueous bedforms: A new look at an old problem. Journal of Sedimentary Research, 61, 160–172], forming a dune set in the flood season. Large dunes occurred predominately in the surveyed area of the estuarine zone, and two-dimensional dunes predominated in the dry season while three-dimensional dunes prevailed in the flood season. Sharp lee sides of dunes have low angles, indicating a significant suspended-load transport for the bedform migration, and the majority of them face down-estuary reflecting the controlling process by the ebb current. The bed material migrations in terms of relative maximum gross transport show a satisfactory agreement with the sonar mapping in the dry season. The relative maximum gross transport as an independent estimator of migration direction, can be used to effectively determine the bed material transport directions in the Changjiang Estuary. [Copyright &y& Elsevier]