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.

In recent years, the operation of cascade reservoirs in the upper reaches of the Yangtze River led by the Three Gorges Reservoir has significantly changed the low water level of Dongting Lake, which has had an adverse impact on the water resources and ecological security in the lake area. As a result, the low water level situation of Dongting Lake is drawing more and more attention. Based on the abundant and long-term daily observation data of Dongting Lake and main stream of the Yangtze River, the spatial and temporal evolution characteristics of low water level in the Dongting Lake area since the 1950s were analyzed in this study, especially during the storage period of the Three Gorges Reservoir. In addition, the influence of the jacking effect of the Yangtze River on Dongting Lake was also discussed to analyze the impact of the Three Gorges Reservoir. The results show that the annual minimum water level in the Dongting Lake area over the years generally occurs from January to February and December. Since it is not within the storage period of the Three Gorges Reservoir, it is not affected by the Three Gorges Reservoir. However, the average water level in September and October during the main storage period of the Three Gorges Reservoir has significantly reduced, and the closer it is to the main stream of the Yangtze River, the greater the influence is. In recent years, affected by the advance of the impounding period, the average water level has decreased further in September. In addition, the low water level of Dongting Lake is obviously affected by the jacking effect of the main stream of the Yangtze River. After the impoundment of the Three Gorges Reservoir, the water surface slope of the Dongting Lake area has decreased, while that of the main stream of the Yangtze River has increased. This has strengthened the jacking effect of the main stream. The research results can provide reference for the solution of water resource and ecological crises in the Dongting Lake area.

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.