| Loess landslides and debris flows are the most frequent geological disasters in Lanzhou and Longnan areas,especially the short-term extreme rainfall has caused great threats to casualties and property losses in these areas.However,it is very difficult to accurately predict the occurrence of landslides and debris flow hazards,due to its special geological environment and climatic conditions.Simultaneously,the most important factor is the current post-disaster prevention project in the geological disaster prevention system in Lanzhou and Longnan.The update and development of monitoring and early warning technology gradually take the center of the prevention and control system for the regional monitoring of various geological disasters and the early warning of hidden danger points.The aim of this paper is to fully understand the importance of the monitoring and early warning system,and to determine the reliability of the monitoring and early warning platforms in Lanzhou and Longnan,as well as provide data support and theoretical guidance for disaster prevention and mitigation in these two regions.To fulfill this aim,this paper gathered landslide and debris flow disaster data from the National Geological Disaster Data Open Network,Lanzhou Helongnan Land and Resources Bureau and Gansu Provincial Geological Disaster Monitoring Institute.Following,the data of the monitoring and early warning platforms of the two regions is conducted by statistical analysis and research.At the same time,the method of the monitoring and early warning in various regions were concluded by reviewing the literature.Based on limited loss data,the rainfall thresholds of loess landslides,torrents and debris flow disasters were studied in the perspective of rainfall conditions.This paper carried out statistical analysis and research on the monitoring and early warning technology methods,monitoring equipment and monitoring historical data in these two regions based on the platform of Lanzhou and Longnan Monitoring and Early Warning Demonstration Zones.Meanwhile,according to the technical methods adopted in the area,the effectiveness of the monitoring system in the two areas is evaluated.At the same time,the paper counts the monitoring equipments deployed in various regions,and divides the current operating status of various types of monitoring equipment into three categories,which includes normal operation,abnormal operation(equipment operation,no data collection),and abnormal collection(equipment operation,abnormal data collection),And through the spatial distribution of normal operating equipment,make an evaluation of the monitoring range of the monitoring and early warning platform.By analyzing the historical data of various types of monitoring equipment,the monitoring effect is analyzed and evaluated.According to the type of monitoring parameters,the monitoring and early warning methods can be divided into four categories,which are deformation monitoring,physical and chemical field monitoring,groundwater monitoring and inducing factor monitoring.Both the Lanzhou and Longnan areas are involved,including GPS,mud level,rainfall,cracks,7 types of monitoring equipment for water volume,infrasound and earth pressure.Due to the different geological conditions in the two places,infrasound and earth pressure equipment were not used in Lanzhou,and water content and GPS equipment were not used in Longnan.As total,642 sets of monitoring equipment were used in these two regions,366 sets in Lanzhou and 276 sets in Longnan.The most used monitoring equipment in the two areas was rainfall and water content monitors,with a total of 540 sets,accounting for 84%.Among them,291 sets of normal operation instrument equipment in Lanzhou area,the rate of normal operation is 79.5%,199 sets of normal operation equipment in Longnan area,with 72.1% of the equipment operated normally.From which,it is obvious that the maintenance work of monitoring equipment in Lanzhou area is higher than that in Longnan area.It can be seen from the spatial distribution map of the operation status of monitoring equipment in different regions that the monitoring platforms in different regions can achieve good regional monitoring effect with relatively low amount of data provided by the platforms which increases the difficulty of disaster prevention and mitigation,but also hinders the correct prediction and prediction of geological disasters.By analyzing the historical data of the normally operating equipment,it can be revealed that the equipment can provide good feedback on the climate,hydrology and surface displacement of various regions.It also verifies the timeliness and effectiveness of the monitoring and early warning platform.Based on average historical data,the paper analysed landslides and debris flows induced by rainfall in Lanzhou and Longnan in the past ten years.Using R-language codes for quantile regression analysis,the empirical rainfall threshold curves of Lanzhou and Longnan were proposed for the first time.Compared with representative rainfall threshold curves of the whole world,as for short-duration rainfall events,landslides are more likely to be caused in Lanzhou area,while long-duration rainfall events are more likely to cause landslides in Longnan area.By studying the system,platform and model of monitoring and early warning in the two regions,it can provide data support and theoretical guidance for the two regions to accurately predict landslide and debris flow disasters. |
