Research On Influencing Factors And Monitoring And Early Warning Methods Of Debris Flow Starting In Volcanic Erosion Area

(1)The large-scale development along the Erdaobai River in the northern scenic spot of Changbai Mountain,which has a larger impact on the scenic spot,is the five channel debris flows developed on the right bank,two slope debris flows,and the occurrence of each debris flow disaster is mostly concentrated in 6-8 month.In terms of spatial and temporal distribution,the debris flow in the No.2 ditch in the area has a large scale of development and a high frequency of outbreaks,which causes the most damage to the northern scenic spot of Changbai Mountain.The No.2 ditch has a longitudinal length of 1.45km,an average width of 350m,an area of 349659m~2,a relative height difference of 665m,and an average longitudinal slope drop of 458‰;the area of the determined danger zone is 0.02km~2.The debris flow proneness score of No.2 ditch is 102 points,which is prone to debris flow,and the type of debris flow is storm gully debris flow,which has a strong disaster-causing ability.(2)The distribution of debris flow in the northern scenic spot of Changbai Mountain is concentrated between 20°-50°,and the vertical drop is roughly between350‰-600‰.The height difference of the debris flow gully in the study area is relatively concentrated at 350-700m.The main reason for the outbreak of debris flow disasters in the study area was caused by heavy rain.The pre-rainfall before the rainstorm generally lasts for tens of days.This type of rainfall form has two main functions for the start of the debris flow:on the one hand,loose accumulations are continuously moved to form under the effect of long-term rainfall The accumulation of the area increases the dynamic reserves of the source;on the other hand,if the source of the formation area is to be transformed into a destructive debris flow,it needs strong surface runoff formed by rainfall to excite it.(3)The scale of the physical simulation test model is 1:100,and three test conditions are set:the intensity of rainfall in a decade to a century,the intensity of a rainfall in a 50 year,and the intensity of a rainfall directly exceeding a century.Under the three test conditions,the model test debris flow start process includes:rainfall→surface erosion→runoff→slope foot erosion→source erosion→gully erosion→gully penetration→gully stability→erosion termination.During the whole process,a large amount of erosion occurs during the gully erosion stage,and a continuous gully is formed on the slope,and a large amount of material is moved by the water flow.This stage can be used as a starting point for debris flow.(4)In the three working conditions,the slope foot position of the source soil is most likely to converge the current and reach saturation.The starting stage of the debris flow from cutting trench erosion to gully penetration is as follows:the rainfall conditions over a hundred years precede the rainfall conditions over a fifty year period,and finally the rainfall conditions that occur once every ten years turn into a hundred years.When the larger rain intensity causes the source of the accumulation body to saturate earlier and form a larger catchment,the faster the debris flow starts.(5)In the monitoring plan for debris flow disasters in the northern scenic spot of Changbai Mountain designed in this paper,the main contents of its monitoring mainly include the formation conditions and movement characteristics.The designed monitoring methods include rainfall monitoring,infrasound monitoring,wire break alarm monitoring,mud level monitoring,soil moisture monitoring and video monitoring.(6)The debris flow in the northern scenic spot of Changbai Mountain experienced heavy rainfall on the same day,and there was small-scale rainfall 10 days before the outbreak.Three kinds of rainfall parameters,such as rainfall intensity,historical cumulative rainfall,and early effective rainfall,were selected to construct the rainfall threshold for debris flow.It is concluded that in the study area,the hourly rainfall exceeds 19.7mm,the effective rainfall in the early period exceeds 32.7mm,and the historical cumulative rainfall exceeds 43.5mm,and the debris flow disaster will occur.Finally,the lower limit of the peak rainfall intensity of 19.7mm/h was used as the critical rainfall for the debris flow disaster.