Debris flows and landslides caused by Typhoon Morakot in Taiwan

Typhoon Morakot was "born" on August 4, 2009 at approximately 22.4° N and 133.8° E in the North Pacific Ocean, about 1,000 km far from northeastern Philippines, moving west at a speed of 10-30 km/hr towards Taiwan, landing on Hualien, eastern Taiwan on August 7, and then moving across over northwestern Taiwan on August 8 with a wind speed up to 40 m/s. Unexpectedly, Typhoon Morakot brought severe rainfalls and caused catastrophic disasters, such as a large number of debris flows, shallow landslides, deep-seated landslides, debris dams and inundations in the mountainous areas of central and southern Taiwan. The catastrophic disasters killed more than 700 people. The rainfall brought by Typhoon Morakot was record-breaking, not only on rainfall amount and (Graph Presented) rainfall duration but also on total area covered with high rainfall. For example, the maximum 1-hour, 12-hour, 24-hour and 48-hour rainfalls at Alishan rainfall station were 123 mm, 934 mm, 1623 mm and 2,361 mm, respectively. This paper will report the rainfall conditions when the debris flows and landslides occurred and the characteristics of debris flows in Gaoping river watershed basing on the data of field investigations and satellite image analyses.