| Due to its frequent occurrence,landslide disasters have a huge threat to the natural environment and the safety of people and property on a global scale.Decided by its geological environment and geomorphic features,China is one of the countries with frequent landslide disasters.According to the data released by the Ministry of Land and Resources,China’s geological disasters are severe,especially landslide disasters.Therefore,to mitigate landslide hazards and protect human life and property,landslide hazards studies to achieve disaster prevention and disaster reduction and management are of great scientific and actually significance.Due to its special geological environment and strong human engineering activities,the Three Gorges Reservoir area in the Yangtze River region has experienced frequent geological disasters.This article is based on the Chongqing Municipal Disaster Prevention and Control Center project,taking the bank of the Chongqing section of the Three Gorges reservoir as the research area,through the collection of data and summary analysis,the reservoir bank geological structure is classified,the geological structure of the reservoir bank is studied,and the basic geological characteristics of the geological disasters in the Chongqing section of the Three Gorges reservoir area are investigated.The construction of disaster area database is completed and most relevant index factors are selected to carry out the landslide disaster susceptibility evaluation.Then,based on the results of susceptibility zoning,considered major evoked factors(rainfalls),risk analysis of landslide hazards under different rainfall return periods are carried out;Finally,based on quantitative and qualitative analysis methods,the assessing and analysis model of reservoir bank shore risk element are established,and then used to assess the risk of the whole study region.The following conclusions are drawn:(1)The development regularity of landslide hazards in the Chongqing section of Three Gorges Reservoir are analyzed.In terms of scale,the small and medium size landslides are the main disasters in the study area,accounting for 81.06% of the total landslide disasters.Among the disasters,the scale of landslides in FengJie County to YunYang County is relatively large,and WanZhou County to FengDu County are relatively small and the landslide points are dense.In terms of time,landslides mainly occur during the flood season from June to September and are closely related to the rise and fall of reservoir water levels.Based on the geological structure and lithologic distribution,the geological structures of banks among the reservoir segment are divided into four types: the high gorge section,the monoclinic section,the Near-horizontal section and the accumulating section.Among them,the high gorge section has the characteristics of fast sliding,rapid occurrence and huge momentum.As a result,the risks to life and property and the surge risk are very high.The landslide risk of the monoclinic section from FengJie County to YunYang County is also high due to the relatively large scale of landslides and the strong role of the reservoir water level;Landslides are smaller in the section from the Zhong County to FengDu County,which are related to rainfall and reservoir water levels,and the risk of landslide disasters is relatively small.In the Nearhorizontal stratum section,the deformation of the landslide body is mainly creep,for shallow formation dip.Meanwhile landslides are slower,and the momentum is smaller,so effective early warning measures should be taken and the risk of landslide disasters is smaller.The accumulation section in the upper reaches area are prone to generate landslides,which are less affected by the reservoir water level.Because of rainfall and human engineering activities,the size and frequency of these landslides are relatively small,also the risk of them.(2)Because the scope of the study area is large,this paper adopts the unique conditional unit and selects only three hazard indicators that are most closely related to the development of landslide in this area: stratum lithology,slope structure and fluctuating zone.Among them,the influence of the easy-slip friction angle was taken into the account of the slope structure,and the forward slope is further subdivided into: gentle slope,isoclinic slope and steep slope.Based on the information model,the susceptibility map of the study area was obtained.The following conclusion are drawn from the zoning map,1.The high and middle-prone areas are mainly distributed below FengDu country.The main districts and counties in the high-prone areas are FengDu,ZhongXian,WanZhou,FengJie and WuShan.The medium susceptibility area is mainly distributed in the upper reaches of FengDu,WanZhou.The high and middle prone areas are mainly distributed below FengDu country.The high-prone areas are concentrated in FengDu,ZhongXian,WanZhou,FengJie and WuShan reservoir section.The middle-prone area is concentrated between the upper reaches of FengDu and the lower reaches of WanZhou and YunYang section.2.The high and middle-prone areas are mainly concentrated in the sand-mudstone interbed lithological group,as well as the slope structures of the forward slope,the nearhorizontal layered slope,and the smooth slope.3.Following the FengDu country,due to the impact of reservoir water fluctuation and immersion all year round,the floating force and dynamic water pressure of the reservoir water on the coastal rock and soil masses are constantly changing,so landslide disasters are easily induced.But in some reverse slope areas such as WuShan and Feng Jie counties,where landslide disasters are not easy to occur,are extremely low and low prone areas.(3)Based on the results of landslide susceptibility zoning,major risk factors(rainfalls)were considered,landslide hazard analysis was carried out under different rainfall returns,and regional landslide risk assessment was completed.Firstly,the paper statistically analyzes the relationship between the 50 years rainfall data of Chongqing reservoir segment and the annual occurrence of landslide disasters and then concludes that the landslide events show a significant positive correlation with rainfall events.Secondly,Pearson III distribution function was used to fit the rainfall frequency curve of each district,and the rainfall intensity in the return period of 5,10,20,and 50 years in the study area was obtained.Then,combined with historical landslide inventory,the landslide area induced by different rainfall return periods in each susceptibility level was calculated,and then the spatial probability and time probability of landslide occurrence in each vulnerable area were also obtained.Finally,the risk assessment of landslide hazards in the study area under different rainfall return periods was completed.(4)Based on qualitative and semi-quantitative analysis methods,the vulnerability assessment and risk assessment analysis matrix for the Chongqing section of the reservoir were established,and then the risk of the whole region was studied.The vulnerability analysis of disaster bearing bodies mainly includes the landslide intensity and the disasterresponsive capacity of the disaster-bearing element.By establishing the vulnerability analysis matrix of landslide hazards in the study area,the vulnerability of buildings,roads and population were obtained.A quantitative classification of the value of the disasterafflicted bodies in the study area and the distribution of population density,combined with the risk matrix,completed the risk assessment of landslide hazards in the entire region.Finally,the risk level of the project management area is reduced by two levels,superimposed the research area project governance,and the risk distribution map based on the project governance.The following conclusion can be drawn from the risk mapping: 1.The extremely high and high-risk areas are mainly distributed in the monoclinic strata and the steep gully of the Wu gorge section,as well as part of the horizontal strata.2.The low-and middle-risk areas are mainly distributed in the colluvium section,sandstone and carbonate rocks group section and reverse slopes of other reservoir sections.3.In the above areas,the main urban districts of each district and county are relatively high-risk areas because of their large population distribution and large economic value.And the risks have been reduced in the areas where the mitigation projects were adopted. |
