低衝擊開發於降低都市淹水之效率

Abstract

台灣位於太平洋西北側，地處熱帶及亞熱帶氣候區交界，常飽受夏、秋兩季颱風及四月至六月梅雨季所帶來強烈降雨，加上台灣天然特殊地理條件，常造成眾多淹水事件，導致各區域災情及財損影響極大。隨時間推進，台灣整體都市化也趨於一定水準，對於經濟產業可帶來一定的效益，背後對環境所造成的衝擊也無法量化比較。有鑑於此，國內近期治水推動於傳統水利設施的拓建、增設，目的在於減輕現在及未來各種降雨事件所帶來之衝擊，然針對少數極端強降雨或常態性小量降雨，傳統水利設施仍無法顯著改善此類問題。 二十世紀九零年代由美國數發展出的低衝擊開發概念（LID），其特色在於恢復一地區因都市開發後而改變的地文、水文因子，希望達到增加地表入滲、減少不透水面積以減輕地表逕流之目的，整體而言LID在世界各地已被廣泛應用且成效顯著。近期國內吸取國外LID經驗，正編列適宜台灣的相關手冊，希望藉此解決國內水患問題。 相較以往LID相關研究主要小尺度探討都市逕流量之改善，本研究另針對大尺度二維地表淹水情形做分析。整體模擬結果發現低衝擊開發可減輕都市排水系統出流量外，對小於十年重現期距之降雨事件均有效改善地表淹水情形。

Located in northwest side of Pacific Ocean, Taiwan straddles between tropical and subtropical divided. In summer and fall seasons, many typhoons hit Taiwan. Also the monsoon between April and June brings large amount of rain in Taiwan. With special geographic condition, many floods occur that affect inhabitants of the island. By urbanization increasing, it enhances great development in industry and business but on the other hand, it destroyed the environment hugely. To mitigate urban flooding, the government dedicates on building or extending more hydraulic facilities to solve those problems. However, for extreme powerful rainfalls or frequently occurring minor rainfall, those hydraulic facilities had no special efficiency. Low-impact development (LID) technique is developed by U.S. two decades ago. The concept is to recover the hydrologic and geographic condition to the situation of pre-urbanization, by increasing infiltration and decreasing imperviousness to reduce surface runoff. Overall, LID is widely practiced world-wide and has to been found to have great performance. Recently, the government in Taiwan acquires the foreign experiences and is about to publish the LID manual to deal with the inundation issue. In the past, the research of LID focused on analyzing the reduction of surface runoff or micromanagement urban drainage. In this essay, it not only analyzes the reducing of urban drainage but also simulates overland flow to investigate the efficiency of LID. The results show that LID can reduce flood in an urban drainage under the condition of less than 10-year return period rainfall.