土石流災害經濟損失之風險感認探討研究-以南投縣為例

近年來台灣地區嚴重的氣候異常，造成土石鬆動現象，亦引發土石流災害日漸頻繁，如何有效地發展土石流風險準則已是重要課題。當發生土石流災害時，其威脅性增加，危害到南投縣民眾房屋倒塌財產損失之安全，國內已開始持續正視此問題，目前僅水土保持局針對土石流災害，所造成的人命損失部分，訂定風險管理機制及風險準則。但國內外文獻對於土石流經濟損失風險準則探討方面之學術研究尚屬有限，有鑑於國內外發展合理之風險準則需求日增，本研究也將初步探討土石流經濟損失風險準則之研訂。為量化土石流災害事故，利用問卷調查，分析南投縣民眾對土石流風險感認(Risk Perception)之可接受與可容忍不同程度上差異。另外，以F-N曲線圖呈現，作為南投縣民眾針對土石流危害可容忍度指標研擬之參考，討論土石流經濟損失風險準則之研訂。問卷結果可知，不同家戶年收入對其土石流風險感認有具有差異性；與「國家災害防救科技中心」研究結果比較，政府及相關單位的普及宣導，使之防災意識日漸抬頭，對於事前之防災工作，更有助於降低災情的損失。本研究分析所得國內對土石流風險之感認，不論可容忍程度或可接受程度與BC Hydro暫定之經濟損失風險準則寬鬆約一數量級(one order of magnitude)。雖然，本研究可得之歷史災害資料年限有限，且缺極端事件之較高損失，但所得結果已可為台灣地區制定土石流風險準則之參考，以BC Hydro的大壩可容忍曲線為台灣土石流災害可容忍曲線之下界，應屬合理之界限。訂定台灣土石流災害可容忍曲線可考量以本研究所得曲線往下調整0.5至1個數量級，另外考量採用BC Hydro F-N曲線之斜率，繪製較完整曲線，以為暫行考量之準則。

關鍵字

土石流；風險準則；風險評估；社會風險；風險分析；氣候變遷

並列摘要

Debris flow disasters have become frequent in Taiwan over the past years as a result of severe climate condition coupled with the fragile geological environment of the mountain. With the advent of risk based response to natural hazards, it is of importance developing acceptable risk criteria for debris flow disasters. Initiatives by the Soil and Water Conservation Bureau over the years have led to development of the risk management framework for debris flow disaster as well as tentative acceptable risk criteria for fatality. One major consequence of the debris flow disaster in Nantou County is the loss of house. However, relevant studies on the acceptable criteria for financial loss are very limited. In this study, the risk perception on financial loss is investigated and development of the acceptable risk criteria for financial loss also is explored. The risk perception on financial loss for residents in Nantou County and the base data for development of the acceptable risk criteria were acquired through questionnaires. Results of the analysis on the acceptable risk are presented in the form of F-N chart, so that the recommended acceptable criteria will be in line with the quantitative risk assessment. Relevant risk criteria (acceptable and tolerable risks) that can be used for comparison of the analyzed results obtained in this study is limited to those developed for large dam by BC Hydro. In general, the perceived risks for debris flow in Taiwan is less strict by approximately one order of magnitude than those set by the BC Hydro for large dams. The difference is attributed to the hazard types in consideration. However, the stricter criteria may be considered as the lower bond for the acceptable risk criteria of debris flow disaster. Suggestions are made for establishment of the risk criteria for financial loss.