Risk Assessment Of Debris Flow In Dacanggou Dingri County Tibet

In recent years,with the implementation of china's “the belt and road initiative” strategy,the state's economic investment in Tibet has been increasing.However,the regional geologica conditions with frequent geological disasters restrict the development of infrastructure in the region.Tibet has a unique geological environment,especially the regional geological environment of the himalayas,which has attracted extensive attention of researchers.The himalayas are divided into south slope and north slope,the difference between the south slope and the north slope is obvious,the rainfall on the south slope is more than that on the north slope.On April 25,2015,an 8.1 magnitude earthquake occurred in Nepal,which had a serious impact on Tibet,especially in shigatse region.The geological disasters that broke out after the earthquake were ice and snow melting and rainstorm debris flow,which posed a great threat to the production and life of local residents.therefore,it is of great significance to carry out risk assessment of debris flow in this area.Tingri county dacanggou debris flow is located on the southern slope of the himalayas,ice lakes and glacier snow are distributed in the upper,topography,melting glacier snow cover,heavy rainfall in the region and material source conditions constitute the hidden danger of the debris flow gully outbreak,it is a typical “ice snow melting+rainstorm” debris flow gully on the southern slope of the himalayas.In this paper,the debris flow in dacanggou is selected as the specific research object to carry out the risk assessment study of the debris flow gully.The basic characteristics and formation conditions of the debris flow gully are analyzed through literature investigation and field investigation(field visit,aerial photography by unmanned aerial vehicle,remote sensing photography,etc);Combined with fuzzy comprehensive evaluation method,the risk degree of the debris flow gully is given quantitatively;Through Massflow numerical simulation software,the hazard analysis of the debris flow gully under different rainfall frequencies was carried out.the main conclusions are as follows:(1)There are three potential hazards of ice lake outburst in the dacanggou watershed,there three ice lakes are prone to debris flow outburst under the influence of sudden strong earthquake activity and abnormal weather(extreme rainfall and temperature rise).(2)The formation of dacanggou debris flow is mainly triggered by heavy rainfall and glacial lake outburst,which belongs to rainstorm(outburst),gully type,low frequency,small-medium(large)and dilute debris flow.(3)Ten evaluation factors were selected,including the maximum rush out,monthly average temperature,basin area of the survey area,frequency of occurrence,length of the main gully bed,maximum relative elevation difference of the basin,glacier snow area,ice lake area,24 hour maximum rainfall and storage of loose materials.the weight of these 10 factors was determined by comprehensive analytic hierarchy process and projection pursuit method,and it was concluded that rainfall and loose material reserves were the main factors affecting debris flow gully outbreaks.(4)Fuzzy comprehensive evaluation method was used to carry out the quantitative risk evaluation of the debris flow gully,combining matrix membership function and trapezoidal membership function.the results show that the debris flow gully is moderately high risk,and the quantitative results are consistent with the field investigation.(5)According to the original DEM data of dacanggou,the grid is divided into 10×10m in Arcgis and converted into ASCII file format.The Massflow numerical simulation software is used to simulate and analyze the dacanggou under different rainfall frequencies,thus obtaining the mud depth,flow velocity,sedimentation range,square quatity,etc,of the dacanggou debris flow,establishing the hazard zoning standard of the dacanggou debris flow,combining the results of the numerical simulation,obtaining the hazard assessment zoning map of the dacanggou debris flow.(6)From the hazard assessment zoning map of dacanggou,it can be concluded that the proportion of moderate hazard and high hazard in the whole debris flow gully is obviously more than 50%,which further verifies the analysis of hazard of dacanggou by fuzzy comprehensive assessment.Finally based on the on-site investigation,fuzzy comprehensive evaluation and numerical simulation results,the prevention and control suggestions for the debris flow in dacanggou are put forward.