A Study On River-Lake Relationship And Flood Control Situation Of The Middle Yangtze River

Flood control and disaster mitigation is a top priority for the harnessing, development and protection of the Yangtze River Basin. Its middle reaches are an economically developed region where flood disasters occur most frequently and severely, and so are a focal point for the flood control of overall Yangtze River Basin, while they are a difficult point too, due to extremely complex relations between rivers and lakes.Due to the change of river-lake relationship, the flood control situation of the middle Yangtze River had been growing increasingly tense in the decades before the Three Gorges Project was built though the flood control system on the middle reaches of the Yangtze River was being completed at the time. Construction of the Three Gorges Project greatly improves the flood prevention capabilities of the middle Yangtze River, especially the Jingjiang section. However, the middle reaches are surely subject to a long-term variation in scoring and deposition after operation of the Three Gorges Project and numerous reservoirs on the upper mainstream and tributaries, causing the change of the relations between rivers and lakes, and then affecting the flood control situation of the middle Yangtze River. It is of great significance to correctly understand the change in river-lake relationship and its impact on the flood control situation of the middle reaches of the Yangtze River, which provides not only a scientific basis for the future overall arrangement of the flood control of the middle Yangtze River, but also a technical support for the joint operation of the Three Gorges reservoir and those on the upper mainstream and tributaries.Considering the long time span and extensive simulation area of this study, a mathematic model was used to analyze the evolution of the middle Yangtze River and associated large lakes on the basis of the numerical modeling of flood routing. In the paper, a deep analysis of the river-lake relationship that affects the flood control situation of the middle Yangtze River is conducted, and the relations between rivers ad lakes are expatiated from the angle of the flood prevention of the middle Yangtze River.The river-lake relationship changes during the 1960s and 1970s and after the 1990s are analyzed. The impacts of the river-lake storage capacity change, the channel flow capacity change and the overall river-lake relationship change on the flood control situation of the middle reaches of the Yangtze River during these periods of time are mathematically modeled separately for numericalThe flood control situation of the middle Yangtze River after operation of the Three Gorges Project is analyzed from two aspects. On one hand, the flood operation rules of the Three Gorges Project at different phases are discussed, and the changes of the flood control situation of the middle Yangtze River during different operation periods of the Three Gorge Project as well as under joint application of the Three Gorges reservoir and those on the upper mainstream and tributaries are analyzed. On the other hand, further analysis is performed for the influence of river-lake relationship changes on the flood control situation of the middle Yangtze River on the basis of the research of river-lake erosion and accretion variations and river-lake relationship changes after operation of the Three Gorges Project.The study suggests that the flood control situation of the middle Yangtze River (especially near Chenglingji) had been growing increasingly tense due to the change of river-lake relationship before the Three Gorges Project was built. Construction of the Three Gorges Project greatly improves the flood prevention capabilities of the middle Yangtze River, which are further enhanced with successive completion of numerous reservoirs on the upper mainstream and tributaries. However, the middle reaches and associated lakes are surely subject to a variation in scoring and deposition as well as a change in river-lake relationship and in the spatial-temporal distribution of surplus flood after operation of the Three Gorges Project and numerous reservoirs on the upper mainstream and tributaries, which may adversely affect the flood prevention of certain areas. On the other hand, due to an acute imbalance between the flood in the Yangtze River characterized by high peak and large volume and the limited channel flow capacity of the middle reaches, there is still a large volume of surplus flood needing to be well handled in the case of heavy floods even after the Three Gorges Project and numerous reservoirs on the upper mainstream and tributaries are put into operation. Therefore, comprehensive measures consisting of embankments, reservoirs, river regulation and flood storage and retention areas should be taken for the flood control of the middle Yangtze River.