| The karst mountain region of southwest China is one of the largest karst areas in the world,which has an area of 620,000 km2,and the geological environment is extremely fragile.Guizhou Province,located in the center of China's karst mountains,about 73% of which is covered by typical karst landscapes,is one of the least developed regions,and the number of poor villages ranks first in China.Under the pressure of large population and craggy mountainous,deforestation,land reclamation,steep slope farming and overgrazing are commonplace in Guizhou Province.The fragile geological environment as well as the over-exploitation,has caused serious soil erosion in the role of rainfall.Owing to the strong soil erosion,the annual increments of rocky desertification area is 933km2 and the annual loss of sediment is 196 million tons in Guizhou Province.As a result,larger and larger surface is broken and the soil is loose,which creates favorable conditions for the formation of geological disasters.Especially in the Bijie region,due to its typical karst geomorphic features,it forms the medium high mountain gorge with steep slope.Accounting for 15% of the land in Guizhou Province,there are 35 debris flow hidden dangers,which accounts for nearly 1/3 of the total debris flow hidden points in Guizhou Province,being the main outbreak of debris flow points.In this paper,Ertang river and Changchong village basin are selected as the study area.Based on the disaster status quo and the interrelations of soil erosion,landslide,collapse and debris flow in the study area as well as the soil erosion model and the soil erosion modulus of the study area,the sensitivity of the debris flow in the study area is evaluated,which provides the decision-making basis for the local government to prevent and control geological disasters.At the same time,a method for the debris flow sensitivity evaluation in small basin of karst area is summarized as follows.1.Analysis of disasters interrelations in study area based on field investigationThe results of field investigation show that soil erosion is the most widespread and serious type of disaster in the study area,while the landslides develope less in the study area.The landslides are dominated by small-scale soil landslides on both sides of the channel,mainly induced by steep slopes and rainwater infiltration;The collapse is concentrated in the rivers and road slopes,mostly due to artificial cut slope.The historical situation of debris flow in the study area shows that the debris flow in the area is low-frequency mass debris flow,and the debris flow source is mainly provided by soil erosion.2.To complete the regional soil erosion modulus estimatesThe soil erosion model based on the general soil erosion model RUSLE was selected,considering the influencing factors such as rainfall erosivity,soil erosion coefficient,topography,human engineering and other factors,to estimate the soil erosion modulus of the study area and the to grade erosion intensity.The average soil erosion modulus in the study area is 5411(t·km-2·a-1),the total soil erosion value is 4.74×105(t·a-1),and the strong and eroded area accounts for 26 % of the tatel area of the study area.The total erosion rate reached 3.04×105(t·km-2·a-1),accounting for 64% of the total erosion in the study area.The total area of micro-and mild erosion accounts for 40% of the study area,widely distributed in the river,river accumulation area and low mountain platforms.3.Propose the model of valley debris flow in the study areaIn this paper,17 debris flow gullies and 10 non-debris flow gullies in the study area are selected as samples.Four discriminant factors,such as erosion intensity,trench area,channel length and valley morphology were selected,combined with field investigation,the weight values of each factor were obtained by analytic hierarchy process.After the values are assigned to the factors,the discriminant values are calculated and the discriminant thresholds are obtained.The recognition rate of the debris flow gully in the study area is 94%,and the input data is convenient to obtain.The application prospect is better.4.To complete the debris flow sensitivity evaluationIn this paper,the sensitivity is defined as the congenital condition × acquired reserve.Corresponding to the topography and provenance factor,selecting the catchment unit as the basic unit of the debris flow sensitivity evaluation,based on the field investigation,the topography and geomorphology factor of the evaluation unit is obtained by GIS platform.Based on the soil erosion modulus of the whole area,the source state factor of each catchment unit is obtained,and finally the results of debris flow sensitivity evaluation are obtained.The study area has 68 catchment units,11 high-sensitive water collection units,the tatel area is 19km2,occupying 22% of the total area of the study area,posing a threat to Changgong Village,Xinjian Village,Pingdong Village and Hair Village;Sensitive areas,medium sensitive areas and low sensitive areas account for 33%,22% and 23% of the study area respectively.5.To complete the area of debris flow valley sensitivity evaluationIn the study area,most of the debris flow gully and the catchment range coincide,which means that the sensitivity of the debris flow valley can be directly expressed by the sensitivity of the catchment unit.In order to fully consider the influence of the size of the catchment area on the overall sensitivity of the debris flow,this paper uses the weighted average algorithm to obtain the sensitivity value of the debris flow basin,which is divided into multiple water collection units.In the 17 gullies,there are 4 debris flow gullies is highly sensitive,concentrated in the middle of the study area,respectively,two reservoirs on the left bank of Pingtang Village and Changgong Village,the right bank of three small debris flow gully;there are 6 debris flow gullies belonging to the higher sensitive debris flow gully,mainly distributed in the middle bank of the left bank and the second pond river basin in the Changqiu village;moderate and low sensitivity debris flow gully has 4 and 3.The research results and the actual survey results are in good agreement. |
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