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Summary: After the Yangtze River was closed by the Three Gorges Project (TGP) in 2003, erosion occurred from the dam site to the river mouth, especially in the middle and lower reaches of the Yangtze River. However, in some local areas of Chenglingji reach which holds the key position for flood management, there is actually deposition in contrast to the expected erosion. In this paper, a one dimensional mathematical model of the river network with sediment transport is used as the tool to simulate flow and fluvial processes. The calculation domain is from Yichang, which is downstream of the dam, to Hankou, the controlling node of flood management, 694km long in total. The model is calibrated based on the field data of hydrology and sediment transport during the period from October 2003 to October 2008. Then the model is utilized to simulate the erosion and deposition of the middle and lower reaches of the Yangtze River in the next two decades, and produce the results of a new river channel after river bed deformation occurs. The typical flood processes of 1954 and 1998 in the Yangtze River basin are used to check the flood management scheme for the research area, and results show that water storage of Three Gorges Reservoir (TGR) and a flood diversion program downstream of the Yangtze River should be taken into consideration. [Copyright &y& Elsevier]

Abstract: A three-dimensional flow-sediment model of the Wuhan portion of the Yangtze River was developed using the EFDC (Environmental Fluid Dynamic Code) in order to study the changing riverbed. The model was also calibrated and validated by daily measuring of the water surface elevation and using suspended sediment concentration data secured from June 1 to September 30, 2004. Based on this model, the mobile sediment on the riverbed was simulated for the high water period of the Yangtze River. The results indicate that erosion is the main issue, with maximum erosion (0.27m) occurring at the banks of Tian Xingzhou. In addition, according to a suspended sediment concentration analysis for the Han Kou Hydrologic Station section of the river, the concentration there increased from left bank to right bank. [Copyright &y& Elsevier]

Abstract: This paper summarizes process-oriented field and numerical studies undertaken on the river plume in the partially-mixed Changjiang River estuary. Both estuarine circulation and tidal asymmetry are of great importance to the fine sediment processes. Mean suspended sediment concentration (C̄) and bottom shear stress are the dominant physical parameters controlling the flocculation and settling velocities (w s ) of mud flocs in suspension. Two important physical processes are revealed by acoustic imaging, i.e. (i) the near-bed impulsive resuspension and (ii) the transport processes driven by fine sediment-induced plumes during a spring tide. A turbidity maximum, associated with a suspended sediment front, is observed. Its formation is caused mainly by tidal asymmetry, near-bed periodic tidal resuspension and turbulence suppression by suspension/salinity stratifications. A conceptual sketch of the turbidity maximum is cautiously proposed for the Changjiang River estuary. Four different settling velocity equations, taking flocculation into account, have different effects on the modeled concentration profiles of fine sediment: apparently, Cao and Wang (1994, pp. 252–253) would be the best for spring tide and Thorn (1982, Fig. 3/page 66) for neap tide. Both tidal acceleration and tidal deceleration have strong effects on the concentration profiles of fine sediment within the Changjiang River estuary. [Copyright &y& Elsevier]

Abstract: In this study we applied 40Ar/39Ar dating methods to muscovite grains in sands from the modern Red and Yangtze Rivers in order to constrain palaeo and modern erosion patterns and sediment transport processes. Micas in the headwaters of the Red River and its southern Da River tributary are dominantly Cenozoic, while the northern Lo River tributary shows a typical 160–220Ma population. The lower reaches of the Red River comprise 53% of such Triassic grains, indicating that the Lo River is the most important net contributor to the modern delta. However, this contrasts with zircon U–Pb data indicating that the upper reaches of the Red River dominate that mineral group. We suggest that the mismatch reflects the rapid transport of mica relative to zircon in the river and the fact that the Red River is not in equilibrium. We hypothesize that the zircons were eroded >8ka under a regime of stronger monsoon that enhanced erosion in the northern drainage basin, while modern erosion is focused in the south, especially in the Song Chay Massif. Micas from the upper Yangtze River are resolvably older than those in the Red River (230–250Ma), so that this method could be used to test for drainage capture in palaeo-delta sediments. Micas in the modern Yangtze delta are generally much younger than those in the upper reaches and indicate that erosion in the Longmen Shan (Sichuan) and neighbouring regions is more important than the upper Yangtze in supplying sediment, reflecting the stronger monsoon rains in those areas. [Copyright &y& Elsevier]

Abstract: This paper presents a three-dimensional (3-D) numerical model to simulate morphological changes in alluvial channels due to bank erosion. A method for the simulation of bank erosion is established. This is incorporated into a 3-D mathematical model for turbulent flow and non-uniform, non-equilibrium sediment transport. This model is applied to simulate morphological changes in the Shishou bend of the middle Yangtze River in China, where serious bank erosions occurred during the last two decades. The double-layer sediment structure of the riverbank on the middle Yangtze River is taken into account in the bank erosion module. Both cohesive and non-cohesive bank material in the different layers are considered. The bank erosion module also includes other factors affecting the rate of bank erosion, such as the longitudinal length of failed bank, the thickness of each layer in the double-layer structure, and the erosion-resisting effect of cohesive material from the top layer of failed bank. A locally-adaptive grid system is proposed to efficiently simulate the lateral migration of alluvial channel due to bank erosion. The predictive capability of the 3-D model is examined by laboratory data. Simulated processes of bank erosion agree with field observations in the Shishou bend during the period of October 1996–October 1998, and the bank erosion module plays a significant role in simulating morphological changes of the study reach. In addition, the equivalent channel-forming discharge, which is defined as a constant discharge that can create the same amount of bank erosion in an alluvial channel as that created by natural runoff processes during the same period of time, is proposed to improve calculation efficiency for feasibility studies. [Copyright &y& Elsevier]

Sand extraction from the mid-lower Yangtze has increased rapidly since the 1980s, in contrast to a rapid decrease in sediment discharge from the Yangtze River into the sea. In-channel sand extraction poses great risks to flood protection, navigation channels and railway bridges. This paper reviews the recent history of in-channel sand extraction, discussing the present status and potential problems in legislation and management. It is concluded that the share of interests, the involvement of local criminal gangs and official corruption were the main difficulties for the ban on illegal sand extraction. It is proposed that the sites and amounts permitted for in-channel sand extraction should be re-evaluated under the new sediment budget after closure of the Three-Gorges Dam. It is necessary to explore the use of alternative materials in order to reduce the demand for natural sand while meeting the market needs for socio-economic development. [ABSTRACT FROM AUTHOR]