| The study area is located at the southeastern margin of the Tibetan Plateau,at the junction of Sichuan,Yunnan and Tibet.The study area is profoundly influenced by tectonic movements and experiencing rapid uplift and deep cuts because of the unique geographical location makes.The conditions of the broken bank slope,high and steep terrain,and the rapid downcutting provide a natural geological basis for the landslide and landslide dam.A large amount of water energy is stored in the study area and its surroundings.13 large-scale hydropower projects have been planned to be built in the upper reaches of Jinsha River,which is the important sources of west-east power transmission.The medium and large hydropower stations planned and constructed from downstream to upstream in the study area include Benzilan Hydropower Station,Xulong Hydropower Station,Changbo Hydropower Station and Suwalong Hydropower Station,among which Suwalong Hydropower Station has been put into operation in 2022.Therefore,it is of far-reaching significance to do a good job in the identification,investigation and compilation of landslides and river blocking in the area,and to fully tap the value of all kinds of collected information,and to draw relevant disaster sensitivity and risk assessment maps.At present,regional research related to landslides mostly focuses on assessing the occurrence and spatial distribution of landslides.But the results are less involved in the further use,such as for the study of the possibility and the hazard assessment of river blocking.In this paper,the landslide susceptibility assessment and the event-based river blocking case study were integrated.In order to reveal the scientific problems of the causes and distribution of the landslide and river blocking in the valley section of the rapid uplift area,a scientific system model was established from the identification,inventory,investigation and research of the landslide and river blocking to the landslide hazard assessment.In this study,the Air-ground technology(remote sensing interpretation,In SAR and field survey),dating technology and experimental technique were applied.ENVI,Flow-3D,Arc GIS,RHINO,SPSS,Origin Lab and other softwares were used.The concept of “potential hazard unit” was adapted to the research.The final results were verified by quantitative and qualitative methods.The main achievements of the thesis are as follows:1.The research methods of landslides and related ancient river blocking events were summarized and explored,and a more perfect method for analyzing the evolution of ancient river blocking events was proposed.Landslide identification features related to remote sensing interpretation were summarized.Based on the previous research,the landslide data investigated and recorded were further analyzed.Furthermore,several researches have been studied,including the relation between the landslide development and bank slope structure,the law of landslide area and landslide volume,relationship between landslide development and climate change.For the ancient landslide damming river event,based on the team’s investigation experience and previous research,five investigation methods were summarized.The data that need to be investigated are discussed,beneficial to make the investigation work more efficient.For the more complex multiple river blocking evolution in the typical section of SuwalongWangdalong in the study area,the means of mutual verification were proposed to analyze the evolution history of river blocking,including elevation inference analysis method,dating data grouping analysis method,field typical geological phenomenon interpretation method,river break point analysis method and residual accumulation body stability analysis method.Finally,according to the obtained inventory and dating data,the spatial and temporal distribution characteristics of landslides and related river blocking events were analyzed.The results above provide a basis for landslide susceptibility assessment and risk assessment of landslide damming of river.2.The landslide susceptibility zoning map of the study area was drawn,based on potential hazard unit.Considering the ultimate goal and the complex geological background of the rapidly uplifting alpine gorge area in the study area,the concept of potential hazard unit which is more suitable for this study is proposed by combining the slope unit and the basin unit.Compared with the results of the traditional grid unit,its feasibility was proved.Based on the previous results and thousands of related literatures published recently,193 evaluation factors were summarized.17 factors of three kinds of parameters(i.e.geological parameters,hydrological parameters and unit characteristic parameters)were selected according to five principle(i.e.research relevance,accessibility,research maturity,quantifiable degree and non-uniformity).The final result map was obtained by comprehensively applying the gamma operation of fuzzy logic,frequency ratio method and user-defined fuzzy membership degree method.The results was proved to be reasonable by three quantitative indices including ROC(Receiver Operating Characteristic)curve,statistical parameters and kappa coefficient.Combined with SBAS-In SAR technology,the prediction performance of the model was quantitatively evaluated.In the whole modeling process,extreme value of weight and frequency distribution plot were used to judge whether the statistical results are reasonable.In addition,the uncertainty of the model was discussed in depth.The work above contributed to the improvement of landslide susceptibility assessment theory.3.The basic framework of risk assessment of landslide dammimg of river is constructed.Landslide dammimg of river risk assessment based on the basic framework and ideas of landslide susceptibility assessment is a further extension of landslide susceptibility assessment.On the basis of the obtained susceptibility assessment results,the establishment of risk assessment was decomposed into five steps,including the susceptibility assessment of river blocking conditions,the susceptibility assessment of landslide damming of river,the hazard of landslide damming of river,the vulnerability of disaster-bearing bodies and the risk assessment of landslide damming of river.Then the complex model establishment was deconstructed into a simple and easy-tounderstand process.The whole process involved the discretization of river section and the selection of evaluation indicators that can characterize each sub-target layer.Finally,the analytic hierarchy process is used to empower and superimpose the factor layers to obtain the regional landslide dammimg of river risk assessment results.The whole process involves the discretization of river section units and the selection of evaluation indexes that can characterize each sub-target layer.Finally,the analytic hierarchy process was used to overlay the index layers in order to obtain the regional landslide damming of river risk assessment results.For the final results,the reliability of the results was evaluated by comparing with the verification of the river blocking sites and the published results.In this paper,the differences and relations between the eventbased river blocking research and the regional river blocking research were also discussed in depth and detail,and the relevant research theories were supplemented. |
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