| The present study conducted a detailed investigation into Qinling-Daba(Qinba)Mountainous Area in Shaanxi Province and established the cataloging and spatial databases of geohazards for this region by adopting various technological measures known as remote sensing(RS),geography information system(GIS),global positioning system(GPS)as well as the unmanned aerial vehicles(UAV)surveying and mapping technology to collect and organize the relevant data and materials by means of RS interpretation,field investigation and data purchase.The geohazard features specifically concentrated on landslide,collapse and debris flow were analyzed in this study on the basis of previous achievements mentioned above so as to find the hazard-formative conditions in Qinba Mountainous Area in Shaanxi Province by quantitative research method and then carried out the geohazard susceptibility assessment and regionalization according to the research results.Besides all these,the risk management exploring and geohazard controlling measures were also discussed in the study as references.The three main findings of the research are shown as follows:1.Detailed analysis of geohazard features in Qinba Region.1.1.The main types of geohazard in Qinba Mountainous Area are landslide,collapse and debris flow.The landslide is mostly widely distributed among the three,which accounts for86.88%of total geohazards in this region.From the spatial distribution,the geohazards mainly distribute along the rivers and sides of valleys while less distribute in remote mountains and hinterlands.To explore the spatial distribution pattern of geohazard points in this region,Approximate Nearest Neighbor(ANN)was used and the result indicated the intense spatial aggregation in geographical distribution.To further reveal the spatial aggregation features,Arc GIS software was used to conduct the kernel density analysis and results are as follows:(1)The main scale of the landslides and debris flows are small and medium-sized while most collapses are medium-sized.(2)According to the cumulative frequency of areas and volumes in geohazard attacking region,though the number of huge geohazards is small,it controls the total areas and volumes of hazards in this region.(3)The spatial tendency analysis results showed that the areas and volumes of landslides and collapses decline from the south-north to the central part of the region while the areas and volumes of debris flows declines from the northwest to the southeast.(4)From the geohazards'activity intensity,counties or districts in the north of Qinling Mountains as well as Ankang city in southern Shaanxi Province have the comparatively higher activity intensity.Among these counties and districts,Baqiao District,Ziyang County and Lintong District have comparatively higher density in number,while Mei County,Feng County,Hanbing District have comparatively higher density in area scale and Linwei District,Mei County as well as Foping County have comparatively higher density in volume scale.1.2.The power-law relationship between scale parameters of landslides and collapses in Qinba Mountainous Area in Shaanxi Province has been discovered.The researcher fitted the relationship between area and volume,area and length as well as area and width with power-law exponent and then provided the empirical equation,which showed that the relationship between area and volume,area and length as well as area and width follows the power-law distribution.Among all these,the area and volume acquires the best fitting result.Therefore,the disaster area and volume could be quickly estimated by these easily acquired scale parameters,such as length or width,which are of great practical importance in geohazards preventing,controlling rescuing and so on.1.3.The fractal features on geohazards were also explored with quantitative analysis in this study.Using box-counting method in constant dimension fractal counting measure,the researcher calculated the fractal dimension of geohazard in Qinba mountainous area,which showed a high fitting degree(R~2=0.946,P<0.05)in double logarithmic curve on the spatial distribution of these geohazard points.The value of fractal dimension,which specifically is0.938,indicates the apparent fractal feature in spatial distribution of these points.The value of fractal dimension in landslide is much higher than the national average known as 0.9062,indicating the higher landslide activity intensity comparing with other regions in the country.1.4.The research took the Fengfenggou landslide as a study case to thoroughly introduce the field investigation on landslides with the assistance of UAV.From the acquired high-resolution DEM and DOM images,the researcher extracted the high-accuracy topographic and geometric parameters.Besides,the distribution of elevation frequency,exposure frequency,slope frequency as well as relief frequency on landslides were statistically analyzed,finding that these frequency distribution curves enjoys the unique strengths in recognizing the structural composition,main slip direction and so on.Therefore,these curves in some way could be used to recognize the potential landslide areas.This study case meanwhile confirmed the promotional value of UAV photogrammetric technology which could successfully fulfill the geohazards field investigation task.2.The study quantitatively explored the disaster formative factors in Qinba mountainous area from the five dimensions,which are known as topography,hydrometeorology,vegetation,geological structures and human activities.Among all these five dimensions,11hazard-formative factors of slope,exposure,elevation,topographic relief,mean annual precipitation,topographic wetness index,distance from river network,vegetation coverage,stratum lithology,distance from fault zone and distance from the road network were extracted to systematically analyze and expound the relationship between the geohazards and impact factors.The findings indicate that the conditions which would easily contribute to the geohazards should be as follows:the area has the slope which may extend from15-35 degrees with the exposure to south,southeast or southwest.The elevation value is below 900 meters.The relief degree should be lower than 35 meters.The mean annual precipitation is around 900-1100 millimeters.The topographic wetness index is greater than 6 and the distance from river network is less than 500 meters.The vegetation coverage is less than 60%and the stratum lithology should be in medium hard,medium soft or soft.The distance from the fault zone is less than 2000 meters and the distance from the road network should be less than 500 meters.3.The geohazard susceptibility assessment system was created to conduct the assessment with the application of weighted information model,frequency ratio model as well as the weights-of-evidence model.The results of the assessment model were verified with the mathematical statistics and ROC curve,which showed that the weights-of evidence model among the three could relatively logically and objectively reflect the geohazard susceptibility in Qinba Mountainous Area.Therefore,the results from weights-of-evidence model with the help of natural breaks classification method were applied in this study to classify the regions into 5 sensitive areas,known as extremely low,low,medium,high and extremely high sensitive area.The result indicates that there are 100 geohazard points,accounting for 1.3%of its total number,in extremely low sensitive area with the size of9636.29 kilometers,taking up 11.3%of the total study area.There are 529 geohazard points,accounting for 6.8%in its total number,in low sensitive area with the size of20594.04 kilometers,which take up 24.3%of the total study area.For the25026.5-kilometer-area with medium susceptibility,which accounts for 29.4%of the study area,there are 1584 points scattered around here,amounting to 20.3%of the total.In addition,there are 2919 geohazard points,accounting for 37.5%in its total number,in high sensitive area with the size of 19893.71 kilometers,which take up 23.4%of the total study area.In addition,there are 2658 geohazard points,accounting for 34.1%of its total number,packed in extremely high sensitive area with the smallest size among the five of10038.37 kilometers,which take up 11.8%of the total study area.Finally,based on the susceptibility assessment,the risk management measures and prevention suggestions in the Qinba mountainous area are put forward. |
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