GIS-based risk analysis of debris flow: an application in Sichuan, southwest China

Abstract

Debris flow is a serious geologic hazard in China. It is estimated that nationally debris flows cause up to 2 billion RMB (250 million US$) in damages and 300-600 deaths and injuries annually. To mitigate debris flow hazards, it is necessary to map, model, and identify zones of debris flow hazards and vulnerability as to inform the local people about the potential risk with a geographic information system. This research presents a regional scale case study modeling debris flow risk (hazard and vulnerability) in Sichuan Province, Southwestern China. In this area, 3,290 debris flows have been identified and the spatial-temporal distribution and activity characteristics of them have been documented. Based on the available meteorological data, a Digital Elevation Model with the rate of 1:250,000 and a regional geological map, the 24-hr rainfall threshold (y) for debris flow occurrence is closely related (significant at 99% confidence level) to the index (x) defined using a geology factor (rock hardness: a) and a topographical factor (channel gradient: d) where y = 21 + 10200 / x, in which x = 2.7 × e a + 1000 × d. The discipline is constructive in developing the rainfall threshold for debris flow activity in remote mountainous areas that lack data. For a given watershed, a four-level debris flow hazard map is developed by comparing the rainfall threshold to the design rainfall intensities with 50-, 20-, and 5-year average recurrence intervals, respectively. The degree of debris flow vulnerability is determined by the watershed socio-economic conditions. A four-class debris flow risk map, at the final phase of the research, is generated by combining debris flow hazards and vulnerability. With the debris flow risk assessment, the Sichuan Province is classified into the slight, moderate, severe and very severe regions, which accounts for 36%, 19%, 20% and 25% of total area respectively.