Morphological Characteristics And Risk Empirical Model Of Debris Flow

Debris flow is a phenomenon between landslide or rockfall and river sediment transport.Debris flow is usually induced by heavy rainfall,and the peak flow is large,which leads to the deposition of sediment on the deposition fan,and causes harm to buildings,infrastructure,and personnel.Tianshui,Gansu province is located in the loess plateau,because of many factors such as geological,rainfall,provides favorable conditions for debris flow development,make frequent geological disasters such as landslide and debris flow in the region,but so far about the type of debris flow,the characteristics of motion process analysis and risk assessment of the study also is less,therefore,it is necessary to carry out related research on debris flow.This study on Niangniangba Town,Tianshui City,Gansu Province,because of the heavy rains in 2013 induced landslides comprehensive field investigation and remote sensing images,aerial drones,laboratory test,obtained the number of landslide-type slope debris flow is 54,the number of erosion-type slope debris flow is 23,and the number of channel is 25,get the morphological characteristics of the debris flow,based on the grain size distribution characteristics of debris flow,analyzed the morphological identification conditions,area-slope curve and main erosion process characteristics of the three types of debris flow,and evaluated the risk of the three types of debris flow,which provides certain theoretical support and data accumulation for the prevention of geological disasters in this region in the future.Through the study of the debris flow in Nangniangba Town,Tianshui City,Gansu Province,the following results are obtained:(1)Among landslide-type,erosion-type and channel debris flow,the content of fine particles is the highest in landslide-type,followed by erosion-type and channel debris flow.On the contrary,the content of the coarse particles is the highest in the channel type,followed by the erosion type and the lowest in the landslide type.(2)Combined with the characteristics of the slope debris flow,modified the ruggedness number(R)of slope debris flow,and the revised results can better distinguish the three types of debris flow.The discriminant results are as follows: the characteristics of landslide-type slope debris flow are the slope of deposition fan is >2.5°,the length of flow path is <330 m,the average mobility index is 0.64;The characteristics of the erosion-type slope debris flow are the slope of the deposition fan is >9°,the length of flow path is <330 m,the average mobility index is 0.59;The characteristics of channel debris flow are the slope of deposition fan is >5°,the length of flow path is >330 m,the average mobility index is 0.39.(3)The area-slope curve can better represent the main erosion process of landslide-type,erosion-type,and channel debris flow.The area-slope curve of landslide-type slope debris flow reflects two erosion processes,one is only a convergence process on the slope,the other is diffusion as the main erosion process.The curve of the erosion-type slope debris flow shows that the convergence erosion process is the dominant position of the erosion type.The curve of channel debris flow shows that channel convergence erosion is the main process.(4)Three types of debris flow channel inundation area and deposition fan area with debris flow volume is a positive correlation,three types of inverse ratio relation with the mobility index of debris flow and volume.Combined with the terrain factor w analysis,the results show that the volume factor has a great influence on the landslide-type slope debris flow,and the diffusion process is the main factor.The other two types of debris flow are greatly affected by topography,and the sliding process is dominant.The volume relation can represent the movement distance of debris flow on the accumulation area.The runout distance of the three types of debris flow is positively correlated with the channel height difference,while the runout distance of erosion-type slope debris flow and channel debris flow is positively correlated with the volume,while the landslide-type slope debris flow is negatively correlated.Each type of debris flow can be represented by the combination of ruggedness number(R).