The case study of debris flow hazard caused by typhoon morakot in taiwan, 2009

Abstract

Typhoon Morakot struck southern Taiwan on August, 8, 2009 with high rainfall intensity and accumulated rainfall as high as 2860 mm for 72 hours. Severe landslides and debris flow hazards were induced. The debris flow cases resulted in severe impacts to local communities were selected for case study, for which field investigation and analysis were conducted. Most severe landslide and debris flow cases originated from the rainfall center, which is Alishan mountain, and distributed with decreasing elevation. The analysis of debris cases were selected by category of watersheds including: Nanshalu, Maya, Dakanuwa villages of Namasha Township, Shinkai and Shinfa areas of Liugui Township, Kaohsiung County, and Chianghuangkern of Nanhua Township, Tainan County, Taiwan. Data analysis of the rainfall records suggested that a linear threshold for triggering of the debris flow could be de ned, and the debris flow associated with low accumulated rainfall usually occurred at the high rainfall intensity, but involving smaller amount of debris transportation. While debris flow occurred at high rainfall accumulation with low intensity usually involved large amount of debris, which cause sever hazard.