The Risk Assessment Research Of Typical Low Frequency Debris Flow In Beijing Mountainous Region

With the high-frequency and widespread debris flow in the mountain areas, China becomes one of the most famous debris flow disasters areas. In history, the low frequency debris flow disasters area caused a great loss of economy and infrastructure in Beijing mountain area. Therefore, the study on the risk of the low-frequency debris flow in Beijing mountain area is imminent.Taking Baimaguan river basin of Beijing as the research object, the article established the low-frequency debris flow risk degree calculation formula in Beijing by conversion assignment function calculation method of the single gully risk. Based on the remote-sensing image, DEM, documentation and Field data from Baimaguan river basin, the article calculated and analyzed the results of the risk degree calculation formula. The mainly completed the content and conclusion are showed as follows:1 On the basis of the characteristics of debris flow in Beijing mountain area, the paper summarized and analyzed the characteristics in Beijing low-frequency debris flow as follow:deposits surface coarsening obviously in gullies, the mean grain size increasing as the growth of the distance; the low-frequency debris flow’s interval always become years or decades; low discriminative validity in gullies cause the increasing of difficulties in discrimination; the disasters awalys damaging seriousiy.2 On this basis, the paper summarized and analyzed the characteristics in Beijing low-frequency debris flow. Such as deposits surface coarsening, low-frequency, low discriminative validity in gullies and damaging serious disasters, etc. On the basis of background data collection and field investigation, the article analyzed the provenance conditions, hydraulic conditions and kinetic parameters of 15 gullies in Baimaguan river basin. The results show that the gross of the 15 gullies is 8.87×106 m3, which squeezes the main channel seriously and always accumulates at the bottom of the slope in upstream and midstream. Rainfall is the main excitation condition for the debris flow of this gully or the whole area. When rainfall intensity ranged between 32.03-40.2 mm/h, the gully is more likely to break out debris flow. By the influence of the provenance reserves. the gully is diluent debris gully and the debris flow density is close to 1.5511-1.6819 g/cm3. Caused by differences on in factors, such as the catchment area, terrain factors, the peak flow is about 45.98-753.98 m3/s and the debris flow scale is about 2.52×104 -41.51×104 m3,which varied in gullies.3 The article established a suitable evaluation system for debris flow risk in Beijing mountainous area with the detailed introduction of the calculation method for the Liu Xilin assessment of debris flows. At first, two new evaluation index selection methods are mentioned to redefine and choose the suitable factors of Beijing low-frequency debris flow risk. By the correlation analysis function of SPSS20.0,9 influence factors and 2 decision factors are chosen to set up a system of debris flow risk factors. For example, the influence factors are made up of main channel length, developmental stage, average slope, limit equilibrium coefficient, shape coefficient, the maximum rainfall in 3h, formation lithology and instability ratio of gully bed, etc. Solid material coefficient of the debris flow gully and the frequency constitute the decision factors. Second, the calculation model is improved and innovated, at the same time, the transform functions of the various factors are fitted for the data standardization process. Moreover, through the principal component analysis function of SPSS20.0, each factors’corresponding weight value are obtained. Finally, the article put forward a calculation formula suitable for the assessment of debris flow risk in Beijing mountainous area:Rd= 0.1169P+0.1072FM+0.1130S1+0.1044S2+0.1187S3+0.0979S4 +0.1119S6+0.1094S7+0.1019S8-0.0915S9+0.1101S10...