Flood disasters related to climate change are becoming increasingly frequent, indicating the potential for repeated future incidence. It is essential to fully understand the causes and mechanisms of flood formation to reduce future losses. By taking the extreme flood in the lower Yangtze River in 2020 as an example and using hydrological and rainfall data of the basin, the formation process and triggering factors of a flood disaster were analyzed in this study. The flooding process can be divided into six typical stages, in which the long duration plum rain season, frequent and high-intensity rainstorms, and high overlapping rainfall areas are the preconditions for flood formation, whereas frequent encounters of floods in the main stream and tributaries of the middle and lower Yangtze River are the decisive factors. In addition, flood drainage along the lower reaches and the jacking effect of the downstream tide level play a role in promoting flooding. During this process, the joint operation of cascade reservoirs plays a key role in the prevention of catastrophic floods. The aforementioned results can provide a reference for flood control strategies in case of similar floods in the future.

The Three Gorges Dam (TGD) in the Yangtze River profoundly regulates the downstream river discharge and sediment load, causing significant river morphodynamic changes since 2003. Understanding such changes is vital for managing the navigational waterway. Using the Wakouzi waterway 190 km downstream from TGD as an example, we examined its decadal hydro-morphodynamic evolution based on hydrological and topographical data collected from the 1990s onwards. The results showed that the suspended sediment load has reduced by 85.8% downstream of TGD, although the annual runoff has not changed. The suspended sediment has become coarser due to depletion of the fine sediment source. As a result, the river channel has been substantially eroded, particularly the deep-water parts of the channel. Erosion of the elongated sand bars has emerged as well, even in the presence of channel regulation works. Consequently, channel degradation has led to a lower river stage under the same river discharge compared with the pre-TGD condition, particularly in the dry season with a lower river discharge. These changes imply worsened navigability of the examined riverbend. The results of this study have implications for management of other river reaches in the middle Yangtze River and other rivers undergoing similar changes worldwide.

The construction of cascade reservoirs is associated with considerable uncertainty in sedimentation in the fluctuating backwater area of the terminal reservoir and poses challenges to water safety. The sedimentation characteristics under the influence of multiple factors in the main urban area of the Chongqing river section were analyzed as a case study for the operation of cascade reservoirs in the Jinsha River via the utilization of a large dataset spanning back to the normal storage of the Three Gorges Reservoir. The results of this study indicate that, owing to factors such as upstream water, sediment inflow, reservoir operation, and river sand mining, this river section experienced deposition on the sand bars and erosion in the main channel. The rate of sedimentation increased with sediment inflow, peak flow rate, and duration, while the location of sedimentation shifted as the concentration ratio changed. These results may provide technical support not only for the operation of the Three Gorges Reservoir, but also for the governance of the fluctuating backwater areas of other cascade reservoirs.

The main flow migration in the middle Yangtze River occurs in most river sections and is affected by factors such as incoming water and sediment, riverbed boundaries, and channel shapes, leading to a complex riverbed evolution. Revealing the controlling factors and analyzing the developmental trends are important for addressing the adverse ecological impacts caused by these changes. Based on a large amount of observational data since the impoundment of the Three Gorges Reservoir, the characteristics of the main flow migration in the middle Yangtze River under different flow conditions were analyzed, and its correlation with the nodes and bars at the inlet, the plane shape of the river, and riverbed morphology were determined to identify the key controlling factors. The results showed that it is characterized by the displacement of the main flow zone during the middle-flow period. The key factors controlling the main flow migration include the deflecting action of the nodes and sidebars at the inlet, relaxation of the channel plane shape, and resistance difference caused by the riverbed morphology between the branches. The trend analysis suggests that the main flow migration in the middle Yangtze River may become more frequent after the operation of the cascade reservoirs in the future and may threaten the ecological environment.

Due to the influence of distance, there is a lag effect of channel erosion and deposition in the far reaches of the lower reaches downstream from the reservoir. In this paper, the scouring and silting characteristics of Wuhan reach in the middle and lower reaches of the Yangtze River after the impoundment of the Three Gorges Reservoir was analysed based on the five times plane topographic data. The results show that although there is some scouring in this reach at the beginning of the impoundment of the Three Gorges Reservoir, the intensity is not large. With the increase of the operation time of the Three Gorges Reservoir, the scour gradually develops to this reach, and the scour intensity increases greatly, but it is still concentrated in the basic channel.