低衝擊開發設施的空間配置對於逕流削減之效益評估

近年來面對因全球暖化導致極端氣候事件的短延時強降雨事件頻率增加，而使得淹水事件頻傳。在現行基地保水法規的規範下，仍無法避免新建案所增加的都市雨水逕流。唯有透過低衝擊開發(Low impact development, LID)設施的設置，才得以減少都市地區面對極端氣候事件下所面臨之威脅。本研究以低衝擊開發設施中之綠屋頂為例，並以美國環境保護署(U.S.EPA)開發之暴雨管理模式(Storm Water Managenment Model,SWMM)，作為模擬分析之工具，以臺北市內湖區的環山排水分區作為研究區域，配合當地土地利用相關的背景參數設定，設計不同比例綠屋頂配置百分比（平均配置於子排水分區）之情境與不同比例下兩種空間配置（集中於上游或下游）之情境，模擬各種情境下的綠屋頂的設置對逕流與洪峰流量之削減效益。結果顯示，在78.8[mm/hr]的設計降雨下（台北市排水設計標準），10%不透水面設置綠屋頂且平均分布於子排水分區的情境可分別消減洪峰及總逕流量達5-7%及5-8%，且因此可承受降雨強度達84 [mm/hr]之事件，而不超過排水設計標準；80%不透水面設置綠屋頂且平均分布於子排水分區的情境可分別消減洪峰及總逕流量達46-55%及46-52%，且因此可承受降雨強度達118 [mm/hr]之事件。削減的程度及提升降雨強度的容受能力隨著綠屋頂所佔不透水面百分比的增加而線性增加，平均每增加10%的綠屋頂，可以分別削減6.1%及6.7%的總逕流量及洪峰流量，且因此可多承受4.4[mm/hr]的降雨。然而綠屋頂的空間配置對於削減洪峰流量的影響較為顯著，但整體逕流的削減效率不若直接增加綠屋頂配置百分比。研究結果顯示，綠屋頂能有效的降低因日益增加短延時強降雨事件下所引發之都市逕流。

關鍵字

低衝擊開發；逕流削減；暴雨逕流管理模式

並列摘要

High-intensity rainfall events have been increasing owing to global warming and the consequent climate change, resulting in more frequent flooding. Although there are legal regulations to limit surface runoff after constructions, surface runoff inevitably increases compared to pre-construction condition. Low impact development (LID) facilities are the solutions to reduce the impacts of flooding from the urban development. In this study, Storm Water Management Model (SWMM) was chosen, and green roof, one of the LID facilities, were used as an example to evaluate the effectiveness of runoff reduction at the given spatially-distributed scenarios. Huan-Shan Drainage District, Neihu, Taipei was the study area. Spatially-distributed scenarios included uniformly-distributed green roof (where could be placed) within the drainage district and centrally-distributed in the upstream/downstream area of the drainage district. The results showed that at the design rainfall, i.e. 78.8 [mm/hr] (the design standard for the drainage system in Taipei), total runoff and peak flow could be reduced by 5-7% and 5-8%, respectively, if 10% of the impervious surface was uniformly placed with green roof. In this case, the drainage system could hence tolerate 84 [mm/hr] rainfall event without surpassing the drainage capacity. In the case of 80%, total runoff and peak flow could be reduced by 46-55% and 46-52%, respectively, and the drainage system could tolerate as much as 118 [mm/hr]. The reduction rates of total runoff/peak flow increased linearly with the increase of green roof placement percentages. At the increment of every 10% green roof placement, the total runoff and peak flow could be reduced by 6.1% and 6.7%, respectively, and the drainage system could tolerate more rainfall, i.e. 4.4[mm/hr]. There was no distinct difference among the centrally-distributed scenarios compared to the uniformly-distributed ones, although centrally-distributed ones resulted in relatively more reduction for the peak flow. The results supported the effectiveness of green roof on reducing the surface runoff, which could be practically applied in the urban to reduce the threat of increased high-intensity rainfall event.