The mountain area accounts for 30% of the land area globally, with more than 5 000 people dying each year from flash floods. China’s flash flood disaster control zone covers 48% of the land area, with the living population accounting for 44.2% of the country’s population. Since 2 000, about 1 000 people in China have died each year as a result of flash floods, and the number of deaths from flash floods accounts for about 70% of the death toll from flood disasters. A mountain area often shows the characteristics of steep terrain, broken surface, thick soil layer and frequent rainstorm, and thus, the mountain flood and sediment movement coupling causes the disaster to be prominent because of the steep rise and fall of the flood and the dramatic changes of riverbeds. The prevention and control of flash flood disaster has become a prominent problem to China’s major infrastructure constructions such as agriculture, energy, transportation and national defense security, regional social and economic development and the safety of people’s lives and property. The study of rainstorm and flash flood disaster is still the focus of flood control and disaster reduction in China. Facing the severe disaster risk situation of flood and sediment transport, it is difficult to solve the problem of disaster prevention using the traditional theory and technology of sediment movement, which do not consider the actual coupling process of flood and sediment. In fact, there is not enough understanding of the catastrophic effect of sediment supply mutation on major flash flood disaster. Nowadays, the mechanism between flood and sediment transport coupled into the disaster area identification is unclear, and the prevention and control technology of flood and sediment disaster is not perfect in mountain area. Therefore, it is urgent to systematically sort out the law of flood and sediment transport in rainstorm mountain, by realizing the theoretical innovation of the coupling disaster of flood and sediment movement, putting forward the effective measures of source control and regional comprehensive prevention of major flood and sediment disasters, and significantly improving the technical level of flood and sediment disaster prevention and control in China. It will provide theoretical basis and technical support for safeguarding the safety of major projects in the country and the safety of people’s lives and property. The research on early warning theory and prevention and control technology of rainstorm and flash flood disaster has been studied mainly by rainfall-runoff-water level analysis, taking the critical rainfall/water level threshold condition as the criterion, and less involving the severe adjustment mechanism of riverbed caused by the mutation of sediment supply. But a large number of rainstorm flash flood disaster scene shows that the coupling between sediment supply and flood is the key source power of major flash flood disaster. The project “Research on flash flood disaster under the mutation of sediment supply” is based on the field investigation of rainstorm and flood disaster in mountainous areas and the inversion simulation of disaster experiment. Through the theoretical analysis of hydrology, soil mechanics, hydraulics and river dynamics, in combined with the numerical simulation, the applicants will investigate the coupling disaster process of storm flood in typical small watersheds, sediment from landslide, gravel and pebble transport with a large range of size distribution and the excess sediment supply in a gully. The characteristics of storm flood and sediment in mountain regions, the complex transport power of the riverbed, the water and sediment motion and channel response patterns with excessive sediment supply will be systematically investigated. The response disaster mechanism of rainstorm flood process in the mountain region and the mutation of sediment supply will be clarified. The forgoing researches will provide theoretical and technical support for the early warning and prevention of flood disaster in the mountain region, and will enrich and perfect the hydrological sediment motion and the disaster prevention method during the flood disaster.
