A catastrophic debris flow occurred in Nansalu Village during Typhoon Morakot on August 9, 2009.After the event, we conducted field investigations and interviews with local residents to explore the magnitude and the process of the debris flow. We propose equations to obtain both the peak velocity and the deposition volume of the debris flow. The outdoor deposition depths of destroyed buildings exceeded 2.5 m, and the ratio between the indoor and outdoor deposition depths for damaged buildings was approximately 0.73. The impact of boulders and large woody debris accompanying the snout should be considered in vulnerability assessments of buildings. When the deposition depth exceeds 1.5 m, fatalities increase both indoor and outdoor for residents. Both older adult women and infants are at higher risk when debris flows occur. Strategies to reduce the vulnerability of buildings and residents are also proposed
in this study.
Key Words: slopeland disaster, debris flow, vulnerability, deposition depth