The efficiency of a risk reduction program for debris-flow disasters – a case study of the Songhe community in Taiwan

Abstract

Abstract.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. Although evacuation measures cannot reduce the size of hazard zones, they effectively increase the resilient capacity of residents. The benefit-cost ratio for mitigation structures exceeds 1.0 for both torrents with an average of 3.87; the benefit-cost ratio for evacuation measures is markedly greater than 1.0. Combining mitigation structures and evacuation measures increases the total benefit with a benefit-cost ratio of 4.38. Analytical results showed that the risk reduction program is cost-effective.

Spatial scan statistics in vulnerability assessment: an application to mountain hazards

“…Nevertheless, the results are in accordance with earlier studies on vulnerability of buildings exposed to torrent events in the European Alps (e.g. Fuchs 2008;Quan Luna et al 2011;Totschnig et al 2011) and beyond (Liu 2006;Chen et al 2010). These studies were focusing on a dependency of the damage ratio on the process magnitude and were targeted at the deduction of a general functional relationship between these two parameters.…”

Risk assessment of debris flow in Yushu seismic area in China: a perspective for the reconstruction

“…Consideration of all elements at risk is only practicable for research cases focusing on a small area, e.g. with a toe length less than 1 km (Sterlacchini et al, 2007;Chen et al, 2010). It is not practicable for the Jiegu township which extends 20 km along the Zhaqu River.…”

Planning and Legislation

“…Maps were produced showing affected areas as a red or yellow hazard zone based on sediment deposition depth and can be used to analyse expected property and life losses. The program has had the effect of restraining community expansion into the most hazardous areas and thus decreasing the risk to the community (Chen et al 2010).…”

“…• zoning restrictions in debris flow-prone areas of Taiwan-used in conjunction with engineered mitigation structures to reduce the size of hazard zones-which have restrained the expansion of communities into highrisk areas. Land in hazardous areas can not be developed for buildings but can be used as farmland (Chen et al 2010).…”