防洪工程之成本效益與風險評估－－以基隆河流域整治計畫為例

THE COST-BENEFIT ANALYSIS AND RISK ASSESSMENT OF PUBLIC PROJECTS: A CASE STUDY OF THE KEELUNG RIVER BASIN INTEGRATED FLOOD CONTROL PLAN

有鑑於臺灣近年來颱風洪水災情的頻繁，區域水災防治工程計畫已經成為政府與民眾所共同關切之重大議題。本研究以「基隆河整體治理計畫」為例，引進巨災保險業在分析保費時所使用的全或然率模型之概念，進行洪災損失之風險評估。評估方法除了利用國科會所研發之電腦模擬的淹水潛勢圖檔資料外，也透過各種社經與土地利用之地理資訊圖層資料庫之套疊，以及由實際調查資料建立受災之住宅區與工商業之淹水深度損失曲線， 勾勒出完整的全年累計損失之超越機率分配圖， 最後並利用風險決策理論推導出之工程最適水準條件式， 進行「基隆河整體治理計畫」之成本效益評估， 評估結果顯示在本研究的假設下， 目前政府在基隆河流域所規劃之防洪治理計畫具有相當的淨效益。

Due to the rising damages caused by recent typhoons and flooding events, regional flood control projects have become common concerns for the government and public. This paper introduces a fully probabilisticmodeling technique into the flood loss assessment and cost-benefit analysis of flood control projects, using the Keelung River Basin Integrated Flood Control Plan as an example. Computer simulated flood hazard maps from the National Science Council were used in conjunction with the GIS-based census data and land uses information for the flood risk exposure analysis. The estimation of direct flood damages to residential and commercial buildingswere based on the depth-damage functions established by previous surveys on the disaster areas. Furthermore, an aggregate loss exceedance probability curvewas presented for a complete assessment on annual overall losses. Finally, a decisionmaking theory under risk is used to derive the optimal investment level, aiming at improving the cost and benefit assessment of a flood control project. Themethods and empirical results froma case study on the Keelung River Basin Integrated Flood Control Plan form a supporting basis for the existing flood management strategies by the government.