Study On The Gemetry Of Small Woody Debris In Debris Flow And Its Adsorption Effect On Debris

The typical alpine valleys and high vegetation coverage in the study area,combined with the interaction of the subtropical monsoon climate causes frequent debris flows in this area.After the debris flowing in the Dongyuege and Shawa,various woody debris of different sizes was left in the movement path,and the large woody debris with diameter of more than 0.1 m and length of more than 1 m was often found at the upstream of the channel.The number of large woody debris in the middle and downstream of the channel is significantly reduced,and the small woody debris with diameter of less than 0.1 m and length of less than 1 m formed by large woody debris colliding,scraping,and breaking is significantly increased.Domestic and foreign scholars' researches on large woody debris mainly focuse on its blocking effect on debris flow while few researchers focus on the relationship between small woody debris and debris flow activities.Thus it is urgent to carry out a deep exploration.According to the field geological surveys and the interview of disaster witnesses along the way,the process of debris flow in this study area was basically clarified,and the meteorological data in the study area before and after the disaster were obtained.Through on-site sampling combined with laboratory analysis,by focusing on the two-dimensional axial coefficient,profile index,shape factor,two-dimensional fractal dimension of the woody debris and the surface electric field of the woody debris and the surface charge of the particles,the two-dimensional shape and fractal characteristics of small woody debris below 5 mm trapped in the debris flow accumulation in the study area was explored systematically.And the mechanism of small woody debris adsorbing debris particles was investigated.The study of the geometry of small woody debris in the debris flow and its adsorption on debris particles can help to clarify the significance of the small woody debris in adsorbing rock debris,promoting the debris slurrying and maintaining,facilitating the occurrence,remote migration and ultimate disaster of debris flow.The main conclusions are as follows:(1)The small woody debris of debris flow in Dongyuege have been identified into four main types: plant xylem,plant branches,fibrous roots and plant bark-leaves.The type of small woody debris wrapped in the debris flow of the Shawa is relatively simple,mainly for plant xylem,which is due to the size of the debris flow.(2)The two-dimensional morphological parameters(shape factor,profile index,two-dimensional axial coefficient)of the xylem of plants below 5 mm in the Dongyuege and Shawa showed a positive correlation with the size of the grain size,and Shawa is much more correlated.In addition,the two-dimensional morphological parameters of the other types of woody debris in the Dongyuege have a certain correlation with the size of the grain.The correlation of the two-dimensional morphological parameters and the roots and plant bark-leaves are as follows: It increases(positive correlation),and the branches become smaller(negative correlation).On the whole,the two-dimensional morphological characteristics of the small woody debris in the debris flow of study area are as follows: the high degree of angular bulging,the good rod shape and the poor regularity.In terms of fractal features,the surface features of woody debris are good,and the surface of each type of woody debris is more complicated than regular patterns.(3)The two-dimensional shape and fractal characteristics of the small woody debris in the debris flow of study area are also the important factors affecting the adsorption.The smoother the two-dimensional shape contour,the closer the value of the fractal dimension is to 1,the more unfavorable to the woody debris adsorption debris.(4)Based on the laser particle size analyzer(Beckman Coulter LS 13320)and the results of the burning experiment,we conclude that as the grain size of the woody debris increases,the amount of debris particles adsorbed by the debris flows decreases,and the xylem adsorption of the plants is the highest(Shawa is more than the amount of xylem adsorption in Dongyuege),the bark-leaf is second,the roots are the least,and the branches are less adsorbed than the former two.In addition,the larger the plant xylem size,the coarser the debris adhered thereto.(5)The differences between the surface roughness,contact area,wettability and number of pits of various types of woody debris,its molecular surface electric field and debris,the role of the surface charge of the mineral can account for the difference in the amount of adhering debris.(6)The addition of small woody debris can promote the formation of debris slurry and maintenance.And it also promotes the remote migration of debris flow and the expansion of its scale and thereby increases the harm of debris flow.