Hazard Assessment Of Debris Flow In Post-earthquake Highway Based On RS And GIS Technology

After the Wenchuan earthquake,debris flow disasters occurred in high-intensity earthquake areas,which seriously threatened the lives of residents,restricted engineering construction and hindered economic development.As a "lifeline" for disaster relief and post-earthquake reconstruction,under the influence of extreme weather such as heavy rainfall,the highway is extremely vulnerable to the post-earthquake debris flow,which seriously affects road safety and operations.Aiming at the risk assessment of post-earthquake debris flow along the highway in the quake zone and revealing the law of formation and distribution of post-earthquake debris flow are not only an important part of engineering planning and prevention of mountain disaster,but also a relatively weak link in the field of debris flow research.This thesis taked the G213 line(Wenchuan-Maoxian Section)as the research area.Through data collection,processing and analysis,the formation conditions,disaster mechanism and influencing factors of post-earthquake debris flow in the study area were summarized;the time-series remote sensing image processing and analysis were used to establish remote sensing identify the signs to extract the source information of debris flow;the powerful spatial analysis function of GIS was used to find the law of debris flow activity after the earthquake;frequency and source quantity were calculated and the flow calculation model was revised;on this basis,the evaluation index system was constructed,and the sub-basin method was used to divide the evaluation unit.The gray correlation analysis method and the influencing factor superposition method were combined to carry out the mapping and evaluation analysis of the post-earthquake debris flow risk zoning.The main results and conclusions of this thesis are as follows:(1)Through the geological hazard data and feature analysis,the remote sensing identification mark was established,and the decision tree model was established by using the spectral features of each object to realize the debris flow source information extraction in 2008-2018.Based on the spatial statistical analysis and statistics of debris flow provenance information,it was concluded that in areas with elevation<3000m,slope of 10°-60°,distance from structure<2000m,distance from water system<500m,lithology of soft rock and serious vegetation damage,the possibility of inducing post-earthquake debris flow was greater.(2)According to the evolution law of remote sensing extraction of debris source information,the debris flow frequency was extracted.The debris source quantity was calculated by the model of the relationship between source area and thickness.The flow calculation formula was modified by linear fitting.The weights of each index was calculated by the gray correlation analysis method.The final range of hazard index of post-earthquake debris flow was[1.134,3.289].(3)Based on the post-earthquake debris flow risk index,the study area was divided into five dangerous zones:extremely low(Ⅰ),low(Ⅱ),medium(Ⅲ),high(Ⅳ)and extremely high(Ⅴ).The results showed that there are 86 mudslides with moderate risk and above,with an area of 1557.69km2,accounting for 71.1%and 73.9%of the total and total area respectively;41 debris flow ditches along G213 were in medium or above risk zones,accounting for 95.6%of the total along the road.The overall potential risk of the region is relatively high.The results can provide basis and support for post-quake debris flow dynamic monitoring,disaster assessment,disaster prevention and mitigation,and guarantee the safe operation and effective management of the G213 line(Wenchuan-Maoxian section).