Study On Development Characteristics And Discriminant Model Of Debris Flow In The Upper Reaches Of Dashi River,Beijing

Debris flow is the most serious and destructive type of geological disasters in Beijing.The cause of its formation is complex,sudden outbreaks,and extremely harmful.In recent years,debris flow that occurred during the“7.21”and the“7.20”have brought to local residents a huge disaster.According to different classifications,there are many classification schemes for debris flow.Generally speaking,the“debris flow”actually includes three types:water-rock debris flow,mud-rock debris flow and mud-like debris flow.In this paper,through the collection of data and field investigations,it is verified that there are 72 debris flows in the study area,and 52 mud-rock debris flows,20water-rock debris flows.From the determined types of debris flows,41 randomly selected as the sample to establish the discriminant model,and the remaining 31 types of debris flows as the test sample are used to test the reliability of the discriminant model.Mainly achieved the following understanding and results:(1)In the field survey,according to the sedimentary characteristics,source conditions and topographic conditions of the debris flow.It is known that the type of debris flow in the upper reaches of the Dashi River includes mud-rock debris and water-rock debris flow,it is dominated by mud-rock debris flows.(2)According to the analysis of the relationship between debris flow development and watershed characteristics,the drainage area of the debris flow in the study area is generally less than 4km~2,the main line straight length is mainly distributed between 1~4km,and the relative height difference of the watershed is between 500~900m,The slope of the basin slope is between 30 degree to 36 degree.In the Relief ratio,the difference between the two types of debris flow is obvious.The Relief ratio of the water-rock debris flow is generally less than 250‰.The Relief ratio of the mud-rock debris flow is also distributed between 150‰~250‰,but it is mainly distributed between 300‰~350‰.(3)After screening the relevant parameters of the discriminant model,the Melton ratio(R)and the Relief ratio(Relief ratio)are determined as the discriminant model parameters.The discriminant model for determining the type of debris flow in the upper reaches of the Dashi River is:if R?0.33 and the Relief ratio?220‰,the debris flow is a mud-rock debris flow;if R<0.33,the debris flow is a water-rock debris flow.(4)The discriminant model was applied to 31 test sample trenches.The result shows that the model has a successful rate of 74.2%and high accuracy.Although there is a certain error,the model is still reliable.Based on the threshold of rainfall threshold initiated by debris flow,different types of debris flow warning models were established:the threshold for early warning rainfall of mudstone debris flow was160.8 mm;the threshold for early warning rainfall of debris flow was 248.5 mm.