| Jomda County is located in the eastern edge of the Qinghai-Tibet Plateau,with complex geological environment and frequent debris flow geological disasters,which seriously threatens the infrastructure and lives and property safety of the main population residential areas in the inter-mountain valley mouth,and hinders the development of local social economy.Therefore,it is of great practical significance to carry out debris flow susceptibility evaluation for disaster prevention and mitigation in this region.In this research,the temporal and spatial distribution and development characteristics of debris flow disasters are obtained through remote sensing interpretation and field investigation.Combined with the regional geological environment of Jomda County,the disaster-inducing conditions of debris flow disasters are analyzed.Based on the factor correlation analysis,the appropriate influencing factors were selected,the analytic hierarchy process-information content and the ALSA evaluation method of geo-disaster vulnerability analysts were used,and the small watershed evaluation unit was used to evaluate the vulnerability of debris flow disaster in Jomda County.The main contents and results of this thesis are as follows:(1)The scale of debris flow disasters in the region is mainly small,and most of them belong to the rare debris flow of rainstorm type in mountainous areas.They are mainly distributed along the Ziqu,Duoqu,Jinsha River and its main tributaries.In space,they are mainly distributed in Ziga Township and Qingnidong Township in the central and southeast of Jomda County.Affected by the season,they are concentrated from June to September.(2)Combined with the regional geological environment background of Jomda County,15 factors related to the development of debris flow in the study area were quantitatively analyzed from the four aspects of topographic conditions,material source conditions,water source conditions and human engineering activities.It was found that debris flow was mainly distributed in steep slope(23-28°),large topographic relief(0-20°),southwest slope direction,large basin area(42-64km~2)and large melton rate(0.001-0.005).Weak rock and soil type,geological structure development,1-2km away from the fault structure,basin erosion index is larger(11.56-14.79),terrain humidity index is larger(6.38-8.32),vegetation cover is smaller(0.24-0.33);rainfall is abundant,mainly distributed in the range of 475-525mm;in the basin with abundant surface water system and high river density,the river density is 2.68-6.58(strip/km~2);the closer the road is,the more debris flow develops,mainly in the distance of0-500m.It provides a basis for selecting evaluation factors of debris flow disaster susceptibility.(3)Selecting the unit of small watershed evaluation,the correlation analysis of debris flow hazard factors was carried out.Eight factors were selected,including basin slope,fault structure distance,engineering geological rock group,basin area,river density,topographic humidity,vegetation coverage and rainfall.The analytic hierarchy process-information method was used to evaluate the vulnerability of debris flow.The results showed that the extremely high vulnerability area was 2567.38 km~2,accounting for 19.50%of the total area,the high vulnerability area was 2974.94 km~2,accounting for 22.60%of the total area,and the medium vulnerability area was 2117.94 km~2,accounting for 16.09%of the total area.low-prone areas account for 27.07%of the total area;extremely low incidence area 1940.51km~2,accounting for 14.74%of the total area.The evaluation results of ALSA disaster-prone analysts are as follows:the extremely high-prone area is 1491.55 km~2,accounting for 11.33%of the total area;the high-prone area is 2814.69 km~2,accounting for 21.38%of the total area;the medium-prone area is 4034.42 km~2,accounting for 30.65%of the total area;the low-prone area is 3173.59 km~2,accounting for 24.11%of the total area;and the extremely low-prone area is 1649.84 km~2,accounting for 12.53%of the total area.The high-prone area of debris flow mainly distributed in the southeast and central part of Jomda County,Jinsha River Basin,tributary zigzag and multi-curve basins.(4)ROC curve was used to test the evaluation results of the two kinds of debris flow disaster susceptibility.The AUC value of the two evaluation methods was higher,indicating that the accuracy of the evaluation results was higher.The AUC value of the analytic hierarchy process-information method was 0.907,and the accuracy was higher.However,the evaluation process was complex.The AUC value of ALSA evaluation results was 0.879,which was lower than that of the traditional mathematical model.However,it can overcome the problem of continuous distribution of subjective factors and factor sensitivity in the classification of evaluation factors.It can quickly and automatically evaluate,and provide scientific basis for early warning and prevention of geological disasters in places where human beings cannot reach in emergency relief.(5)In remote sensing interpretation,the area with obvious slope erosion is mainly distributed in the high prone area of debris flow,indicating that slope erosion provides certain material source conditions for the occurrence of debris flow.Under heavy rainfall,there are hidden dangers of debris flow disasters,which should be paid attention to in disaster prevention and mitigation. |
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