Study On The Flood Risk Management And Technology Of The Small Mountain Watershed

China, which is located in the southeastern part of Eurasia, is a world-renowned East Asian monsoon climate zone. Frequent rainstorms occur in the summer in China. China is a mountainous country with a large mountainous area about two-thirds of the national land area, far above the world average. China is also a populous country. Population in mountainous areas accounts for about one-third of the country’s total population and the social economy of mountainous areas is an important part of the whole nation. Storm characteristics of China’s East Asian monsoon climate zone, the complexity of the mountainous terrain and geological conditions, as well as mountain socio-economic development status, lead to the frequent occurrence of flash floods of geological disasters in China. Flood disasters not only cause devastating damage to the infrastructure of the country, and constitute a great deal of damage and threat to the safety of people’s lives. Flood disasters have become one of the important constraints to the hilly and mountainous areas of economic and social sustainable development.Flood risk management, is a new concept of flood control proposed after the mid-20th century. Since the mid-20th century most countries and zones in the world threatened by the flood, have implemented flood risk management strategy. China also started a strategic shift from flood control to flood management after the flood in1989. However, current implementation and research of flood risk management measures, and related technologies, are mostly for the middle and lower floodplains of major rivers. Research on flood risk management for the small mountain watershed receives relatively little focus. The flood risk in the small mountain watershed has significantly different characteristics with that in the middle and lower floodplain of the major river. Therefore, it has a very important practical significance to research flood risk management and related technology in the small mountain watershed for improving flood risk management in the small mountain watershed, effectively reducing casualties and economic losses caused by flood disasters.This paper starts from the status quo of the flash flood control work in China, analyzes the problems in the flash flood control in China, proposes the need for study on flood risk management in the mountain watershed. The basic concept and theory of flood risk management is first illustrated, and then the different characteristics of flood risk in the small mountain watershed are analyzed. Aiming at the technology difficulties facing by the flood risk management in the small mountain watershed, flood risk assessment techniques and monitoring and early warning technology are specifically studied. Specific research and results are as follows:(1) On the basis of a comprehensive exposition of the basic theory of flood risk management, the characteristics of flood risk in small mountain watershed are analyzed. Nowadays socio-economy in mountainous areas is in rapid changes of urbanization and industrialization, which, on the one hand change the structure and characteristics of flood risk in the mountainous areas, and change the original low-risk areas into a high-risk areas; and on the other hand put forward higher requirements on the flood control security. The small mountain watershed flood mostly caused by the mesoscale heavy rainfall has a sudden surge characteristic and is a small scale event in time and space. The characteristics of flood risk in the small mountain watersheds leads to big technical difficulty and uncertainty in flood risk assessment and early warning of the small mountain watershed flood.(2) The extraction techniques of small mountain watersheds and their features are studied based on GIS. The small mountain watershed is the place of flash floods and is the basic unit of flood risk analysis and management. In this paper, the idea of the small watershed extraction based on a fixed point and considering the impact of flood control projects is put forward. This work provides an important basis for the flood risk analysis and management in the small mountain watershed.(3) The small mountain watershed flood risk assessment techniques are studied. Mountain watershed flood occurs mostly in remote mountain areas and so lack of effective observation of hydrological data that the hydrological model is difficult to be established. The technology roadmap for flood risk assessment and map of the small mountain watershed is studied and established. This research has much practical value to improving the flood risk management in small mountain watersheds.(4) The technological difficulties in monitoring and early warning of floods in the small watershed are analyzed and the heavy rain flash flood warning indicators are researched. Rainstorm flash floods in the small mountain watershed are always small-scale events in time and space, so that the traditional hydro-meteorological observation and forecasting and early warning still exists large technical difficulties and uncertainties. A new method to determine the rainfall criteria leading to the flash flood in the small mountain watershed are put forward in the paper.(5)The County-level Flash Flood Monitoring and Early Warning system (CFFMEWS) is introduced. The County Flood Control Department is an important responsibility in the defense of flash flood disasters in the small mountain watershed. Therefore CFFMEWS has a very important role to improve operational capacity of County Flood Control Department in monitoring and early warning of flash flood. An event-driven County-level Flash Flood Monitoring and Early Warning system is put forward and is applied in Luanchuan, a county of Henan province.