Reserach On Landslide Risk Assessement And Management In Wanzhou District

Because of the complexity of geological environment and the time-space differences and uncertainty of the mechanism of geological hazards,it is difficult to predict the occurrence time,the occurrence place,the volume and the influence area of geological hazards accurately based on the recent theoretical and technical level.Therefore,it is still a challenge to ensure the safety of residents and protect their properties in geological hazard areas.According to this situation,it is urgent to find out effective ways to make pre-disaster decisions of geo-hazards.Thus,research on geological hazard risk assessment and management will be the right thing and of great significance to realize the prevention and control of geo-hazards.Wanzhou District is the second largest city in Chongqing,and it is also an important part of the Three Gorges reservoir area.In recent years,with the cooperation and efforts of the Three Gorges Command Center,Wanzhou District Land Bureau and the local township offices,Wanzhou geological hazard risk management system has been built in the main,but still faced with some problems,such as disaster prediction difficulties,imperfect management measures and so on.Therefore,this paper will focus on the study of landslide risk assessment and management,analyze the state of art of landslide hazard risk assessment and management and summarize previous research results,in order to carried out the research on regional landslide risk assessment and management in Wanzhou district.The results of this paper will play an active role in guiding geo-hazard prevention,control and management in Wanzhou district and other regions of China,and have important theoretical and practical significance.This paper summarized the state of art of landslide risk assessment from two aspects,which were landslide hazard and risk assessment and landslide hazard and risk management.The difficulties in the present study of this field has been pointed out.The geological environment background of Wanzhou district was systematically analyzed from the aspects of geography,meteorology and hydrology,topography,stratum lithology,geological structure,neotectonic movement,hydrogeology and the characteristics of landslides in Wanzhou district.Besides,the methods which had been commonly used in assessing landslide risk were introduced by every main procedures according to the flowchart of regional landslide risk assessment.This procedures include landslide risk assessment index selection,landslide susceptibility analysis,vulnerability analysis,landslide risk analysis and landslide risk acceptability criteria making.Afterthat,landslide risk in Wanzhou district has been analyzed by considering three different risk analysis models and different rainfall scenarios and then landslide risk assessment was carried out based on other researchers' results of landslide risk acceptance criteria.Tangjiao NO.1 landslide was taken as an example to produce individual landslide risk assessment.Firstly,the landslide was partitioned by stability status and the failure probability of each part was calculated under four water level and rainfall scenarios.Secondly,under the most dangerous condition,landslide and its secondary disaster risk assessment has been carried out.Additionally,the status quo of geological hazard risk management in Wanzhou district was analyzed and the main methods of geological hazard risk management in China was introduced.Then,the countermeasures of landslide risk management in Wanzhou area for two scales,regional scale and point scale,were put forward.The innovation points in this paper includes: regional landslide risk has been assessed dynamically by considering the proper ability of rainfall induced landslides,individual landslide and its secondary disaster risk has been assessed according to the characteristics of landslide hazard and risk in Three Gorges Reservoir,the risk management strategy has been studies on both regional and point scales by the combination of geology and management disciplines.The main research results of this paper are as follows:(1)The main research difficulties on landslide risk assessment and management were summarized.Based on the analysis of the previous research,the main research difficulties on landslide risk assessment and management were summarized from three aspects,there are regional landslide risk assessment,individual landslide risk assessment and landslide secondary disaster risk assessment.The difficulties were mainly in the insufficient research in the aspects of refinement,quantitative and standardized.In addition,from the aspects of methods and applied objects,the research difficulties has been put forward,for instance,it was difficult to determine the risk acceptance criteria,etc.(2)The characteristics of landslide formation and distribution in Wanzhou district have been obtained.Based on the analysis of landslide history data,the related geological and meteorological data in Wanzhou district,the characteristics of landslide formation and distribution in Wanzhou district have been obtained.In this study area,most landslides were soil landslide and mainly formed in medium size.Besides,the landslides are mainly developed in the form of dustpan shape on the plane and convex and stepped shape on the profile.The material of the landslides are mainly derived from the Quaternary slump,alluvial deposit and residual sediment.The material of the soil landslides are composed of silty clay,while of the rock landslides are composed of sandstone or sand-mudstone interbeds.The sliding belt mainly developed in the sandstone-mudstone contact surface except for the weak structural surface.The slide bed is mainly developed on the Upper Jurassic Shangshaximiao Formation(J2s).The deformation and failure mechanism of the landslides in study area are mainly based on progressive damage.In addition,from the perspective of spatial distribution,the landslides in Wanzhou district mainly distribute along the Yangtze River and its tributary in a striped pattern,along the slope elevation in vertical zonal pattern,and concentrate in dip slope in anticline area and in urban construction area.From the perspective of temporal distribution,the annual average percentage of landslide occurrence in Wanzhou district increased obviously after 2003,and the average percentage of the landslide occurred between 2003 and 2007,while the water level fluctuated between 145-156 m,was slightly higher than that after 2007,while the water level fluctuated between 145-175 m.Meanwhile,the landslides in the study area occurred mainly in June,July,August,followed by May and September and October.(3)Regional landslide hazard and risk analysis and assessment in Wanzhou has been carried out.According to the framework of producing regional landslide hazard and risk analysis and assessment,landslide susceptibility analysis,landslide hazard analysis,the element at risk vulnerability analysis and the element at risk value estimation have been carried out and landslide risk maps in Wanzhou have been obtained.Based on the previous research of risk acceptability of landslide hazard,the risk of landslide in Wanzhou has been assessed.In the previous steps,based on the selection and classification of landslide hazard susceptibility evaluation index,the landslide susceptibility map was obtained by running three models,including the logistic regression model,the support vector machine model and the decision tree model,the landslide hazard map was obtained based on the analysis on rainfall induced landslide probability by considering three different rainfall scenarios and the element at risk vulnerability map was obtained based on history data analysis and semi-quantitative method.Based on the previous analysis,the area of high risk in economic and people in Wanzhou was mainly concentrated in the main urban area,with belt distribute along the water system,while the area of high elevation was of lower risk.The largest landslide risk of economic and population in Wanzhou was under the condition that daily rainfall was larger than 50 mm,and the annual landslide economic risk were unacceptable while the annual landslide population casualty risk was from acceptable to tolerable.(4)Tangjiao NO.1 landslide and its secondary hazard and risk analysis and assessment has been carried out.Landslide partitioning was carried out by landslide stability status,which was determined based on the analysis on landslide displacement monitoring data.Then the profile of each part of the landslide for calculation was determined.In addition,four water level and rainfall scenarios were determined for landslide underground water simulation and failure probability calculation.Under the most dangerous condition,the scope of the landslide which might slide into the river was found out and the height and the scope of the landslide induced surge was analyzed.Besides,the vulnerability of the element at risk has been analyzed and the value of those elements have been estimated.After that,landslide and its secondary disaster economic risk map and population casualty map have been obtain.Under the most dangerous condition,the area with high level of the risk were concentrated in the central front of the landslide.Meanwhile,under that condition,landslide risk assessment has been carried out and both of the annual landslide economic risk and population casualty risk were reached acceptable level.(5)Strategies and suggestions of landslide risk management in Wanzhou were proposed.The main methods of geo-hazard risk management in China were introduced from the basic concepts and work flow.These main methods were the county-based observation and prevention of geo-hazard and emergency response of landslide.The main problems existed in the two methods were pointed out.Meanwhile,based on data collection and survey in Wanzhou,the present situation of geo-hazards risk management in Wanzhou was systematically analyzed and the main problems were pointed out.Additionally,the countermeasures of landslide risk management in Wanzhou area for two scales,regional scale and point scale,were put forward based on the results of previous landslide hazard risk assessment.From the regional aspect,the countermeasures included strengthening the investigation and monitoring of the landslide hazard in Wanzhou,improving the emergency planning of landslide hazard,strengthening the training of professional technicians,optimizing the organizational structure and assistance model of various functional departments,building the dynamic risk management system,increasing investment of landslide risk control,optimizing the urban construction planning program and strengthening the public education activities and public information services and so on.From the point aspect,the countermeasures included strengthening the construction of monitoring system,and improving the ability of emergency response of landslide and its secondary disaster.