A study of the typhoon-triggered debris flow hazard degree of a single gully

Typhoon-triggered debris flow widely occurs and often causes major disasters, and it is necessary to study its hazard degree. Taking 14 typical typhoon-triggered debris flows in the Wenzhou mountain area as examples, this paper establishes a hazard assessment model of a single gully based on combinatorial factors. Debris flow scale (M), debris flow frequency (F), gully gradient ratio (J), forming region integrity coefficient (C), comprehensive typhoon precipitation value (E) and comprehensive geological factor (G) are selected as combinatorial factors to represent the debris flow hazard degree, and the weights of combinatorial factors with the entropy method are obtained. As the gullies in the study area are low frequency as to debris flow, this study uses the Melton ratio (R) to indirectly determine the frequency (F) of debris flow on different scales of R. The hazard assessment model is applied to the selected gullies, and the hazard degrees are obtained. The results correspond to the actual reality that debris flows in the study area are of low frequency and of middle and small scale, and the gullies assessed as high hazards possesses the geological and geomorphological conditions which is the most debris flow-prone in the region.