設置低衝擊開發設施對都市淹水影響之研究

Abstract

台灣位於熱帶與副熱帶氣候區交界，四面環海，飽受夏、秋兩季颱風和梅雨季的強烈降雨所影響，加上台灣特殊的地理環境，常有淹水事件的發生，導致低窪地區災情慘重。隨著時間的推進與科技的發展，經濟產業為台灣帶來一定的效益，同時也造成了都市化的大幅提升，建物大量興建導致不透水面積的比例上升，多數降雨無法快速滲入地下，造成地表逕流量的增加，地表水流受建物阻隔效應，提高街道淹水之機率。為了減輕各種降雨事件帶來的衝擊，除了設計傳統集中式水利工程設施之外，低衝擊開發(Low Impact Development，LID)技術亦是減低洪水威脅的方式之一。 近年，國內也陸續在土地開發過程及環境整治計畫中納入「低衝擊開發」的概念，並編列完成適宜台灣的低衝擊開發相關手冊。本研究利用SOBEK模式，結合多重尺度網格的配置，在局部細化區域考慮建物與街道流效應，使淹水情形更貼近真實情況，並納入低衝擊開發設施，比較現況、LID設施均勻分佈於模擬區及分佈於高程較低處等三種方案，探討典寶溪下游市區淹水面積之變化情形，模擬結果以LID設施分佈於高程較低處改善效益較佳，並發現低衝擊開發設施對於重現期較小之降雨事件可有效減輕都市淹水面積，其改善效益會隨降雨強度的增加而減少。

Taiwan surrounding by the sea straddles between tropical and subtropical regions, which is often threatened by typhoon or heavy rains in summer and fall. Because of special topography, floods result in grave calamity in low-lying areas. As time progresses and technology develops, economic industry of Taiwan bring not only benefits but urbanization. Surface runoff increases and is accompanied with a higher flood risk since infiltration had is blocked by more and more impermeable area. In order to reduce the impact of rainfall events, apart from the traditional and centralized conservancy facilities, low impact development (LID) technology is one of the ways to reduce flood threats. Recently, the government incorporated the concept of low impact development into the land development process and environmental remediation plan, the manual of LID for Taiwan also accomplished. This study, which combines multi-scale grids, considers the effect of buildings and street flood with fine grids to investigate the urban flooding using SOBEK model. Urban area near the downstream reach of Dianbao River was slected as the target area. Three cases are considered: the existing condition without LID facilities, evenly-distributed LID facilities, and LID facilities at low-lying area. The results show not only the LID facilities at low-lying area is better than the other cases but the LID facilities can reduce more urban flood area effectively under the smaller return period rainfall. The benefit will decrease with the increase of rainfall intensity.