Landslide Risk Assessment In The Three Gorges Reservoir

Since the early and middle2th century, with the large-scale development of social economy, the space scope of human activities expands gradually. And the disturbance degree of major engineering activities to geological environment is deepening constantly. Combined with the influence of the global extreme climate change, the frequency and strength of occurred landslide is in a growing trend. And the caused casualties and economic losses are increasing continually. The complex geological conditions of the Yangtze river Three Gorges Reservoir, the severe human engineering activities, widely development and frequently happened geological disasters of landslide have posed a serious hazard for the Three Gorges Reservoir operation scheduling and the local people’s life and property security, and affect the regional economic development and social stability directly or indirectly. So, to study the Three Gorges Reservoir area landslide risk and to predict the future risk situation and change tendency under the condition of climate changes and human engineering activities are the great and urgent demand of the implementation of disaster prevention and mitigation strategy and to ensure the normal operation of the reservoir. It is of great importance to scientific and realistic significance.The thesis takes the regional landslide risk assessment theory as the foundation, and adopts geographic information system, remote sensing, probability statistics and spatial data mining method as the main technical means, to achieve the purpose of the Three Gorges Reservoir head region (Zigui-Badong segment) landslide risk assessment. On the basis of field investigation, relevant data collection and existing research results, from the perspective of the regional distribution characteristics and typical landslide professional monitoring deformation characteristics analysis, the thesis predicts the landslide happening spatial location, temporal frequency and landslide magnitude to achieve the landslide hazard assessment. It takes vulnerability of elements at risk definition as the starting point, extracting hazard intensity and resistance ability evaluation index system and defining its calculation formula, so as to establish a vulnerability assessment model of elements at risk. It uses economics accounting method to calculate the value of elements at risk, using the quantitative risk model to estimate landslide life risk and economic risk, and to establish risk criteria and evaluate the risk result. Through the analysis of rainfall and land use change rule, the thesis forecasts the landslide hazard and risk change and trend under the condition of future changes, realizing the Three Gorges Reservior head region landslide risk assessment. The main conclusions and results are as follows:(1) The thesis establishes the Rough Sets analysis method of the Three Gorges area landslide spatial prediction and evaluation index system, the Genetic Algorithm-Support Vector Machine susceptibility prediction coupled model and lanslide magnitude analysis model. The results show that the key environmental factors which gestate and affect soil landslide include elevation, slope angle, slope aspect, etc.16factors. And rock landslide consists of17factors, such as elevation, slope angle, morphology of slope, and so on. It proves that different landslide types are affected both by the same environmental factors and different environmental factors. Landslide susceptibility prediction results show that high susceptibility prone are mainly distributed in the Yangtze river from Xiangxi to Badong, and tributary Guizhou river, Tongzhuang river, Qinggan River along the bank and the left bank of Xiangxi river. The field validation and model quality evaluation show that the predicted results are matched with the regional tectonic setting, engineering geological conditions, topography and field investigation situations, etc.. The model prediction results are reliable, and the uncertainty mainly concentrates in the medium susceptibility zones. And the uncertainty of low susceptibility prone and high susceptibility prone is small. The prediction accuracy of soil landslide and rock landslide are86%and85%respectively. Lanslide magnitude analysis results show that the probability of5-6magnitude soil landslide and rock landslide are respectively0.48and0.35. Landslide hazard prediction results show that in the varieties of structure trackway composite parts and new tectonic movement relatively strong area, the areas which contain weak surface (belt) of layered clastic rock and have a weak foundation layer of carbonate rock, as well as rivers along the fold axial development formation of the dip slope and strong human engineering activities are high hazard in landslide. For example, around the Xitan, Shuping to Fanjiapin, around Dongrangkou, near Badong town and Guizhou river, Tongzhuang river, Qinggan River along the bank and the left bank of Xiangxi river, their landslide development have the characteristics of spatial density, high frequency and magnitude, etc..(2) The thesis establishes the vulnerability analysis model of the Three Gorges Reservior head region landslide hazard. The vulnerability analysis results show that the population, buildings, lifeline engineering and land resources in the Three Gorges Reservior head region are high vulnerability. And the high vulnerability of elements at risk mainly focuses in the high hazard landslide area. The life high risk areas mainly distribute in the towns of Badong County, Dongxiangkou, Guojiaba and so on, and also in the densely populated areas such as schools, enterprises and institutions. The economic high risk areas mainly concentrate in areas of the large economic value:the urban and traffic construction land etc.. The risk assessment results show that the unacceptable risk area mainly distributes in towns and villages with a dense population and large economic value of construction land area. The field survey and verification show that the landslide risk assessment results are basically matched with the field disasters. (3) The thesis predicts the Three Gorges Reservior head region mid-and-long term landslide hazard and risk change and trend under the condition of rainfall and land use changes. The prediction results show that the annual rainfall will decrease in the early of the21st century and will increase in the middle and later period. Construction land and forest land will continue to grow. Cultivated land will first increase and then decrease. Shrub land will decrease continuously. The water area will remain stable basically, but there is a small amount of increase. Landslide hazard will be in an increasing trend on the whole, but part of the areas will reduce. And the early hazard changes will mainly concentrate in Badong area, later will transfer to Zigui region. The landslide economic risk will grow sustainably from2010to2050. And in the first twenty years, the economic risk growth is relatively large. The life risk is in a grow trend from2010to2030, and in a degree of drop in the later twenty years.