The Characteristics And Risk Assessment Of Debris Flow In Fault-Affected Areas

The Reshui River basin is located in the south of Liangshan Yi Autonomous Prefecture,Sichuan Province and at the northeast edge of Hengduan Mountain system.The river is the first-class tributary of Anning River and the second-class tributary of Yalong River.Anning River fault zone and Zemu River fault zone intersect in the southwest of the basin.There are many earthquakes around.The continuous strong tectonic activity leads to the extremely poor stability of rock and soil mass,which creates favorable conditions for the formation of debris flow.The lower reaches of the Reshui river are Anning River valley plain,and the middle and upper reaches belong to the landform of medium mountain range river valley with large topographic relief.The disaster area caused by debris flow is mainly located in the middle and upper part.Debris flow disasters have broken out many times in the history of the study area,and there are precedents of death.The lives and property of local residents have suffered heavy losses,and the development of regional social economy has been greatly affected.Therefore,it is necessary to make an objective risk assessment of debris flow in order to strengthen the control and protection.In this thesis,a large number of relevant thesiss have been read and integrated,regional geological background data have been fully collected,and a detailed field investigation has been carried out in the study area.On this basis,the following work has been carried out:(1)According to the existing experience and literature cognition,combined with the onsite investigation in the study area,this thesis makes a qualitative and comprehensive evaluation on the gully in the hot water river basin,selects the part that may have debris flow as the preliminary research object,obtains a total of 33 debris flows,and makes a characteristic summary of typical debris flows.(2)Anning River fault zone crosses the Reshui River basin,and many secondary faults and folds produced by the continuous activity of the fault zone are densely distributed in the basin.Starting from the two of the three elements of debris flow-steep terrain and loose solid source,this thesis analyzes the debris flow disaster effect caused by active faults: In terms of steep terrain,the continuous differential uplifting of fault blocks increases the gradient of the debris flow channel and enables the fluid to obtain greater kinetic energy;the fluid has a highintensity impact force,which can carry more loose objects and erode the channel with a strong scour force.The slopes on both sides of the channel and the bottom of the channel are deposited with soil and rock,which greatly improves the intensity of debris flow disasters.In terms of loose solid provenance,fault zones are active frequently,and faults and fold structures are developed in the basin,resulting in poor rock and soil stability,frequent slope collapse and slippage,providing a large amount of loose provenance for the formation of debris flows;the soil erosion caused by rainfall is more serious;the differential uplifting of fault blocks causes the rock and soil to peel off while the mountain height changes to achieve self-balance,forming a large number of loose solid sources;creep in the geological history of fractures the activity caused plastic deformation of the ridge line in the study area,and the continuous erosion of the channel water on the side of the depression led to the continuous peeling of the rock and soil mass,resulting in a large number of loose solid sources.Therefore,the thesis further summarizes the formation conditions of debris flow in the study area.(3)In this thesis,Open LISEM software is used to simulate debris flows in the Reshui River basin with a return period of 50 years.Using the distribution relationship between human settlements,cultivated land,roads and the impact range of debris flows interpreted by remote sensing image,the managed and basically non threatening debris flows are excluded.Finally,it is determined that the debris flows in Yuergou River,Laowagou,Zhonggou River and Jinergou pose a great potential threat to the safety of local residents’ lives and property,and the above four debris flows were identified as key research objects.(4)This thesis uses Open LISEM software to carry out numerical simulation of the Yuergou River and other four debris flows,and obtains the debris flow velocity and accumulation data of different return periods(once in 20 years and once in 50 years),and compares the data of the two periods.Gouhe,Zhonggou River and Jinergou debris flows will overflow the channel at the same location,greatly increasing the area of debris flow accumulation area.(5)Based on the numerical simulation results of four debris flows such as Yuergou River and their formation conditions,semi-quantitative and quantitative risk assessments are carried out respectively in this paper.The semi-quantitative evaluation adopts the Liu-model and the AHP to calculate the risk of each debris flow and conduct a comparative analysis;the quantitative evaluation is based on the specific relationship between the flow depth and the product of The intensity zoning is done,and the risk assessment is carried out in combination with the probability of occurrence of debris flow,and a hazard zoning map is formed.Finally,the thesis analyzes the evaluation results and puts forward feasible suggestions for disaster prevention and mitigation.