Reveal the Rainfall Type and Critical Rainfall of Debris Flow in Tianchi Area of Changbai Mountain

The Tianchi Scenic Area in Changbai Mountain, Jilin, Northeast China is an area of geohazard of debris flow in several local valleys. To reduce the danger of debris flows, the rainfall process of debris flow in each valley was analyzed by collecting and sorting the debris flow activity data and corresponding rainfall data in local and regional areas. The critical rainfall for triggering debris flow in Tianchi area were characterized, relevant rainfall parameters (hourly rainfall intensity, historical accumulated rainfall, pre-effective rainfall, and rainfall duration) were scrutinized, and the rainfall threshold for debris flow occurrence in the study area was calculated. Results show that the debris-flow-triggering rainfall in the area could be divided into long-term continuous rainfall (LCR) and long-term intermittent rainfall (LIR). The LCR type has long duration of uninterrupted rainfall, and the total rainfall time lasts long. The debris flow potential is gradually built up and burst at last. On the other hand, the LIR type lasts even longer time than that of LCR, the rainfall intensity repeated from zero to the maximum value, and finally triggers a debris flow at water saturation of the debris body. Statistical analysis showed that, to prevent debris flow, the early warning indicators applicable to the Tianchi area can be set as: the historical accumulated rainfall of 43.5 mm or the early effective rainfall of 32.7 mm, and the hourly rainfall intensity of 19.7 mm/h. This study provides a scientific basis for monitoring and warning of debris flow disasters in the Tianchi area of Changbai Mountain.