Abstract:

Debris flow is one of geological disasters in Mountains. Significant damages and losses were often caused by low frequency debris flow.In western region of Sichuan Province 17 debris flow gullies were investigated and particle sizes were measured in the catchments of debris flows.The relationship between coarse particles size and the frequency of debris flows was studied.From the analysis of the characteristics of rock,the coarse particle size and the frequency of debris flows, the conclusions were obtained:(1) the coarse particle size in the formation area is almost the same as the coarse particle size in the deposition area of debris flow catchment. So the coarse particle size in the formation area can be replaced by the coarse particle size in the deposition area;(2) The mean size of coarse particle in middle and high frequency debris flow gullies is less or equal to 20 cm,and the mean size of coarse particle in low and extremely low frequency debris flow gullies is more or equal to 25 cm;(3) The harder rock, the larger coarse particle size is, and the lower frequency of debris flow is;(4) The frequency of debris flow was primarily determined by the characteristics of rock and the size of coarse particles. It is easily and useful to predict the frequency of debris flow by use the characteristics of rock and the coarse particle size in the low frequency debris flow gully:referring to the geological map,judgment the main characteristics of rock,assignment the size of coarse particle,choosing the effected factors,frequency of debris flow could be determined.These works could help to understand and predict the low frequency debris flows