Debris flows in Sichuan province in China two years after the 2008 Wenchuan earthquake

摘要

One of the important points of discussion in the recent disaster mitigation studies is the compound effect of two different types of disaster mechanisms. The present study concerns the compound effect of earthquake and heavy rainfall on slope disasters and a field visit was made of several sites of recent rainfall-induced debris flow in Sichuan Province in China where a past earthquake caused significant slope failures (Fig. 1). It was found that the recent debris flows came from the huge amount of valley deposits that were produced by slope failures during the 2008 Wenchuan earthquake (Fig. 2). Because there still remain debris deposits in the valleys, future risk of debris flow is still high. The risk is made higher when human habitation is located at the exit of a valley and debris flow can directly hit houses and buildings. When the slope surface does not have a stable soil layer, erosion upon rainfalls prevents growth of vegetation and delays the re-stabilization of the slope (Fig. 3). With these situations and the limited availability of financial resources for mitigation of natural disasters, the authors propose the use of inexpensive slope monitoring and early warning for safety of local people (Fig. 4).