Study On Rainfall Threshold And Risk Evaluation Of Debris Flow

Debris flow is one of the most dangerous natural disasters in china,due to the strong destructive ability and the unpredictable property,it may cause disastrous consequences,for the past few years,several events of debris flow inundated people or buildings has reminded us the importance of debris flow researching,in this paper,the information of Dawa gully in Beijing Miyun county is investigated by field survey,we study the geologic environment,and determine the characteristics of debris flow development,combine with outdoor experiment and indoor model experiment,the rainfall initiation critical condition of debris flow has been studied,and we got the critical line of debris flow initiation.by introducing some debris flow samples of china area,the parameters of LAHARZ was optimized,Using the optimized LAHARZ simulation software,the debris flow inundation area of Dawa gully was simulated and we got the prediction map of inundated area,by using the AP neighbor clustering algorithm,the debris flow risk degree of gullies were calculated,and base on the ArcGIS software,the debris flow risk map of dawa gully was obtained through 4 factors,The main contents and conclusions of this paper are::1)Base on the field investigation and analysis of the DEM files,the geologic environment of Dawa gully was summarized,there are 7 large branch channel in Dawa gully,the forming region's gradient of main channel is high,and the debris flow development stages of most branch gullies belong to old,the comprehensive activity intensity and disaster causing ability are in a weak state and with a low susceptibility.2)The rainfall initiation condition of debris flow test model was design and implemented,according to the rainfall condition of 10,50,100 years return period,5 kinds of indoor experiment conditions and 3 kinds of outdoor experiment conditions were designed,through the initiation experiment study on Dawa gully,the variation of the pore water pressure and water content were recorded,combining with the status of debris flow processing,slope erosion,rill erosion,gully erosion were selected to describe the debris flow process point.the gully erosion time point was selected as the starting point,The accumulated critical rainfall values of outdoor test are 88.62 mm,122.88 mm,81.9mm.and the accumulated critical values of laboratory test are 106.98 mm,72.4mm,57.92 mm,87.99 mm,89.5mm.then the debris flow critical rainfall model is got through experiment and historical rainfall data.3)through the analysis of the core thought of LAHARZ flooding model,add some samples of debris flow in china area,study the relationship between the total volume V with cross section area A and plane area B,then the modified inundation model is achieved,by using modified LAHARZ software,the inundated area of Dawa gully was simulated,The results show gully 3-7 have no intersection with residential area,will not have a direct influence on it,gully 1 is closed to residential area,may cause damage,The inundated area of gully 2 has been part in the residential area,The buildings is likely to be buried by debris flow.4)select and quantify the debris flow risk assessment factors,using AP neighbor clustering algorithm to analysis the debris flow risk of Dawa gully,gully 1,4,5,7 are low risk degree,gully 2 and 3 are middle risk drgree,gully 6 is high risk degree.Compared the result with the grey relational analysis,extenics theory,and improved grey correlation,It is proved that the new method can be applied to the classification of debris flow risk5)4 evaluation factors were selected: main channel distance(D1),single channel risk(D2)and simulated inundation area(D3)and rainfall threshold factor(D4),then based on the ArcGIS platform and these factors,the debris flow risk degree map of Dawa gully is calculated.It shows that the risk of the southern residential area is middle risk,and the other areas are low risk.