Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 10 7 2010 10.5194/nhess-10-1591-2010 http://www.nat-hazards-earth-syst-sci.net/10/1591/2010/ http://www.nat-hazards-earth-syst-sci.net/10/1591/2010/nhess-10-1591-2010.html http://www.nat-hazards-earth-syst-sci.net/10/1591/2010/nhess-10-1591-2010.pdf 1591 1603 2010-07-16 The efficiency of a risk reduction program for debris-flow disasters – a case study of the Songhe community in Taiwan S. C. Chen C. Y. Wu d9442006@mail.nchu.edu.tw B. T. Huang Department of Soil and Water Conservation, National Chung-Hsing University, Taichung 40227, Taiwan Taitung Branch, Soil and Water Conservation Bureau, Taitung 95055, Taiwan A risk reduction program was developed after debris-flow disaster analysis is conducted using mitigation structures, evacuation measures and community restrained expansion strategy. The risk assessment method delineates hazard zones and analyzes vulnerability and the resilient capacity of an affected area, allowing the prediction of losses of properties and lives, and the corresponding risk. It can also be used to evaluate performance of a risk reduction program. The proposed method was applied to the Songhe community as a case study to assess debris-flow risk and performance of reduction programs consisting of mitigation structures, evacuation measures and a restrained expansion strategy. Total annual risk decreased to $0.01 million from $0.72 million for the No. 1 Torrent and to $0.36 million from $1.22 million for the No. 2 Torrent after mitigation structures were installed, and evacuation measures were implemented based on restrained expansion. Although mitigation structures are costly, they can reduce the size of hazard zones. Delimitating the Designated Soil and Water Conservation Area restrains community expansion and decreases possible losses. 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