The Development Characteristics And Risk Assessment Of High Debris Flow In Wenchuan Earthquake Area

High debris flow is a special type of debris flow disaster formed under the condition of deep topography in the Tibetan Plateau and the special geological environment of 5.12 Wenchuan Earthquake,which is most developed in the serious area of Wenchuan Earthquake,According to the debris flow disasters occurred in the earthquake area in six hydrological year after the earthquake,most of the serious debris flow valleys belong to the high debris flow,leading to the huge challenge for the earthquake disaster prevention and mitigation.So it has an important significance for research of this particular type of debris flow,also it can provide some theoretical value for the research of debris flow disaster in high earthquake intensity area.The article on the basis of the analysis of the geological environmental conditions of the high debris flow in the study area,focusing on the study of the distribution characteristic and characteristic of causing disaster of debris flow,deeply analyzing the forming conditions,mechanism of causing disaster,movement and activity characteristics of high debris flow,and put forward the risk assessment methods of high debris flow,The main knowledge and achievements are as follows:(1)A large number of “high” slumped masses formed in Wenchuan Earthquake provide abundant material source for the high debris flow;and the research area is located in the border between the plateau and basin which changes rapidly,deep valley,big elevation difference of basin,big gradient of valleys,and the research area is located in the rainstorm area of Lutou Mountain in Longmen Mountain,rainfall is adequate.so it provides great material source,terrain and rainfall condition.(2)The distribution of high debris is mainly effected by landform,stratum lithology,geological structure,earthquake intensity and river basin water system,along the seismic intensity nearby,within the central fracture ? and ? degrees,the minjiang river and tuojiang river upstream of the most concentrated area high deep valley debris flow exposed by scope of hard,and more hard rock is concentrated development.(3)The high debris flow's mechanism of causing disaster is greatly effected bythe changes of basin flow concentration caused by the collapse deposit slip,the start position of debris flow becomes higher,and the clean water area changes to the area of material source;because of the high and steep valley gradient,in the transport process of debris flow,the phenomena of come erosion incised,valley expand and route changing are obvious,and wall collapse amplification characteristic is obvious in the position where the valley is blocked by slumped mass;in the accumulation stage,the position that debris flows rush out becomes higher,and the accumulation position goes from the piedmont gentle slope area to the main riverbed exit position.(4)Through the analysis of the disaster characteristics of high debris flows in six hydrological year after the earthquake,high debris flow has the general activity characteristics of big concealment and sudden possibility,clusters of small watershed is obvious,paroxysmal,long activity time,high frequency of outbreaks,big fluid capacity,easy to form a "high debris flow-barrier lake " disaster chain.Through the analysis of the movement characteristic parameter data of typical high debris flows in research area,fluid weight of high debris flows are generally big,most are viscosity-transition debris flows;due to the change of fluid causing condition,high debris flow's flow velocity,flow amount and the amount of rushing out are obviously bigger than the ordinary one,in view of this,put forward an improved formula for high debris flow's flow velocity and flow amount.(5)According to the formation conditions of high debris flow,select seven indicators of the basin area,valley shape factor,the longitudinal slope,gully blockage coefficient,the density of watershed material source,material source more than 350 m higher than exit of valley and annual maximum 24 h rainfall,establish high debris flow susceptibility assessment model,and make a susceptibility assessment of high debris flow;according to the remote sensing image data,make a interpret of high debris flow,a disaster degree hierarchy,and a disaster assessment of high debris flow;at the last,combine the susceptibility and disaster assessment to make a high debris flow risk assessment results by overlay analysis.