PREDICTION MODEL FOR OCCURRENCE OF DEBRIS FLOWS IN CHANNELS WITH RUNOFF INITIATION MECHANISM

Many debris flows were triggered in and around the Dayi area of the Guizhou province,China during a rainstorm in 2011. High-intensity short duration rainfall was the main triggering factor for these gully type debris flows. They are probably triggered by a runoff induced mechanism. A revised prediction model is introduced for this kind of gully type debris flows. The factors are related to the topography,geology and hydrology(rainfall),and the model is applied to the Wangmo river catchment. Regarding the geological factor,thesoft lithology and loose sediments in the channel are added to the list of the average firmness coefficient for the lithology. Also the chemical weathering is taken into account for the revised geological factor. Concerning the hydrological factor,a coefficient of variation of rainfall is introduced for the normalization of the rainfall factor. The prediction model for debris flows proposed in this paper,delivers three classes of the probability of debris flow occurrence. The model is successfully validated in debris flow gullies with the same initiation mechanism in other areas of southwest China. The generic character of the model is explained by the fact that its factors are based on the initiation mechanisms and the statistical analyses of an unique variety of local factors. The result provides a new way to predict the occurrence of debris flows initiated by a runoff induced mechanism.