Rainfall Conditions for the Initiation of Debris Flows during Typhoon Morakot in the Gaoping Watershed in Southern Taiwan

摘要

In the August of 2009,Typhoon Morakot brought heavy rainfall and caused several landslides,floods and debris flows in southern Taiwan.This work presents the critical rainfall conditions for the initiation of debris flows in the Gaoping watershed of southern Taiwan during the action of Typhoon Morakot,where had many severe debris-flow events during the actions of Typhoon Haitang in 2005,Typhoon Sepat in 2007 and Typhoon Kalmaegi in 2008.Twenty-one debris flow events induced by the heavy rainfalls brought by Typhoon Morakot in the Gaoping watershed were identified by the examination of aerial photographs and field investigations.The rainfall conditions,including the rainfall intensity,the cumulative rainfall,the rainfall intensity-duration curve and the return period of the rainfall,for debris-flows initiation were analyzed and compared with the rainfall conditions of historical debris-flows events in the watershed.The average rainfall intensity that triggered abundant debris flows in the watershed were determined and the relation between the density of debris-flows occurrence and the rainfall characteristics were also presented.