Risk Assessment Of Mountain Torrent Disaster In Small Watershed In Hilly Area Of Hunan Province

Flash flood is an accident caused by excessive rainfall or a dam break or an ice lake outburst,it is often result in casualties,property damage,infrastructure damage and environmental damage.The flash flood disaster is one of the most natural disasters that cause the most death and property damage in the world,it is characterized by sudden strength and rapid disaster,and it is often accompanied byother phenomena such as landslides and debris flows.The risk assessment of flash flood disaster is an effective precondition for predicting the disaster and preventing and controlling it.In recent years,the frequent occurrence of mountain flood disaster in China,the prevention and control of mountain flood disaster is also highly regarded by all levels of government.In this paper,we using scientific evaluation methods to evaluate the risk of mountain torrents in Hunan province,in order to provide reference for preventing mountain flood disasters in hunan province,so as to reduce the loss caused by mountain torrent disaster.In this paper,we takes the hilly area of Hunan Province as the research area,takes the small watershed as the research object,combines the historical flash flood disaster data,and uses the method of information model combining with GIS to study on the relationship between historical mountain flood disasters and flood disaster factors,after that,the risk assessment of mountain flood disaster was carried out.The main contents of this paper are as follows:(1)Hazard assessment of mountain torrents based on the theoretical basis of mountain torrents,it includes the analysis and evaluation of the hazard inducing environment and hazard inducing factors.The risk assessment of mountain flood disaster is the analysis and evaluation of the disaster environment and the disaster risk factors.The evaluation of the disaster environment is mainly to evaluate the natural environment and social environment of the disaster,and the evaluation of the disaster factors is mainly to evaluate the rainfall and human's unreasonable transformation of nature.(2)According to the ASTER DEM data,we use ArcGIS to divide small watershed,and to analyze the morphological characteristics of small watershed.This paper mainly calculates the basic conditions of the five basic morphological parameters,such as roundness rate,gully depth,gully density,Melton coefficient and area elevation integral.(3)Information volume model was established to calculate the information of the six factors:elevation,slope,relief,land cover,soil type and rainfall,respectively from the consideration of three aspects including the terrain,the underlying surface and the rainfall.The information volume of six factors are calculated respectively.Based on the value of information volume of this factors,we obtain the combination of factors with the biggest influence of flash flood disasters.Through calculating the total value of information volume for all small watersheds in hilly areas of Hunan Province,we classify the information volume into five types associated with different dangerous levels.(4)The results show that:The most significant contribution to the flash flood is the artificial surface land cover type,with a information volume of 1.771,followed by the types with relief degree less than 30m as well as the clay soil type(both at a value of 1.331).The mountainous torrent disaster for Hunan hilly area are likely occurred in areas with slope lower than 10°,elevation lower than 100m,relief lower than 30m,whose land cover is artificial surface,soil type is clay and annual mean rainfall is between 1584.3?1662.0mm.Statistics of each level of dangerous areas show that the second-high and the third-high risk types have the largest area in the mountain areas of Hunan,accounting for 26.59%and 26.63%of the total mountain areas,respectively.Area percent of the fourth-high risk types is 20.89%,and that of the first and fifth-high risk types is 13.89%and 11.99%respectively.In the hilly areas of Hunan province,cities with higher risk levels are Yongzhou City,Chenzhou City,Zhuzhou City,Yueyang City,Loudi City and the eastern part of Changsha.The verification of confusion matrix demonstrates that the accuracy rate of this model is 75.36%,indicating a basically credible results of the spatial distribution of risk degree estimated in this study.