Flood Disaster In The Middle Yangtze River: The Reason And Its Management

The most severe flood disaster mainly occurred in the Jingjiang Area and Dongting Lake Area, the upper middle reach of the Yangtze. The historical big floods caused tremendous loss of human lives and properties in Hunan Province and Hubei Province. For the Jingjiang and Dongting Lake Areas, the characteristics of floods, flood control system and flood disaster situation are more complicated than the other areas. Furthermore, since theses areas just locate at the down stream of the Three Georges Project, the flood control situation will be improved dramatically in the near future. Thus, it is necessary for us to research the new ideas and methods to mitigate the flood loss according to the characteristics of the areas. It also has become very important not only for the social-economic sustainable development, but also for solving the similar problems in other basins in China.For the middle reach of Yangtze, the river network, the flood defense system and regime of water level and discharge are extremely complicated. In order to mitigate the flood disaster, firstly, it is necessary not only to study the temporal and spatial characteristics of flood, but also to overcome the difficulties of simulating the flooding situation due to the large area, secondly, the reasonable flood defense strategy must be determined to guide the operation of structural system. Meanwhile, due to the big changes of sediment depositing and scouring, and the river-lakerelationship in the middle reach of Yangtze, it is important to carefully analyze the characteristics of water flow and sediment, the main causes of flood disaster and its tendency, which can provide reasonable and feasible mitigation measures for the middle and long term planning.In this thesis, some researches are done on the study of flood generation mechanisms, simulation of regulating different types of floods, analysis of causes of flood disaster and tendency, and flood disaster mitigation measures. The historical and the latest situations are taken into account, including the influence of Three Gorges reservoir. About the research methods, based on the achieved results before, and overcame the difficulties caused by the complicated river network, river regime and flood defense system, the new methods are applied and description for the characteristics of flood hydrograph is realized. For the tendency prediction, mechanisms for flood disaster generation in the typical areas and its changing tendency are further realized. This thesis includes several special researches, such as combining the latest with the past, the short-term with long-term, and avoiding with harnessing, putting forward new ideas about the causes and tendency of flood disaster in the middle reach of Yangtze, and mitigating measures by taking into account the all factors, including the influence of Three Georges reservoir. In the paper, main researches are as follows:1. About the research methods. By improving the flood routingmethod and the numerical regulation model established before, a model that combines hydrological model with hydraulic model is set up, which can be , properly applied for the flood regulation in the middle reach of Yangtze. Hydrological model has fewer constraints on boundary conditions and local inflow than hydraulic model. But hydraulic model can describe in detail flood hydrograph for detention basins and easily give the water level and discharge at any cross section. Furthermore, its calculation speed and its accuracy are improved..2. About the assessment on the flood defense system and the flood encountering mechanism. Based on the analysis of flood characteristics in the middle reach of Yangtze for different floods in different typical years, design flood for different criteria and types is worked out. According to real flood defense system, the established flood regulation model is put into use to simulate different criteria floods, such as 1954 , 1995 1996 1998 flood and their design floods, with and without Three Georges Project. Then the influence of Three Georges on Dongting area is analyzed.3. About mechanism and tendency prediction. After the historic data being analyzed, the relationship among the transmission of sediment, land use and hydrograph is revealed under the complicated relationship between the river and lake. Also, the degrading mechanism of flooding situation is brought to light. Sediment numerical model is established todescribe the general mechanism of sediment transmission for the long river channel. According to this, the change of flood defense situation in the middle of Yangtze after the Three George Project is put into use is predicted. The conclusion is that the flood defense situation around the Chenglingji and in Dongting area will still be serious.4. About the disaster mitigation measures. According to the mechanisms and influence factors of flood disaster generation, disaster mitigation measures are put forward from the total basin point of view...