低衝擊開發運用在高都市化地區的減洪效益－ 以新北市中永和地區為例

Abstract

台灣位於北迴歸線上，地處熱帶及亞熱帶，四面環海、降雨豐沛，常受到颱風、豪雨的侵襲，除了天然之特殊地理環境，更因都市化導致不透水面積在都市區域比例大幅提升，造成直接逕流量體之增加，以及不透水鋪面造成的水力效率提升，致使洪峰集中，面對洪災的威脅常反應不及，進而危及人民生命財產安全。 有鑑於所有的水利設施及防洪工程建設，皆僅能提供一定程度的保護作用，雨季來臨，特別是颱風帶來之大豪雨及短延時且集中降雨之暴雨，若是降雨或洪水量超出原有的設計標準規模，造成超過排水系統負載之水量而出現溢流現象。故了解都市排水現象，並且採取有效的方法來改善因高度都市化造成之淹水現況，乃為相當重要之課題。除透過此種傳統集中概念下設計之水利工程設施外，藉由低衝擊開發(Low Impact Development，LID)技術，以分散式設施改善土地利用狀況，來減低洪水威脅為一種新興治標方式。 LID觀念於美國推廣大約十多年，實際的應用設施包含：植生草溝、雨水貯留桶、透水鋪面、生態蓄流池及雨水花園等。希望維持或回復基地開發前水文條件的LID，採用源頭管理的理念，以分散、並聯、小尺度的入滲、截流、雨水貯留或滯洪等設施，增加入滲潛勢及延長集流時間，以此策略創造能減少環境衝擊的水文地貌，維持開發前水文條件狀況，如地表逕流、入滲、地表地下水交換等效果。 本研究串聯暴雨逕流管理模式(Storm Water Management Model，簡稱SWMM)與二維淹水模式，模擬各水文事件之地表逕流量、超量溢流量、洪峰流量、洪峰發生時間以及淹水面積，以其為指標模擬數個設計情境，評估LID對於都市排水防洪之效益。研究發現，LID設施取代不透水面積比率越大，控制地表逕流量產生的效果越好，且由於土地對於洪水有一定容受度，LID最大的減洪效率為60%。

Taiwan is located on the Tropic of Cancer which means the island is extended across the tropics and subtropics, and is often threatened by typhoons or heavy rains because of abundant precipitation causing from surrounding by the sea. In addition to our special topography such as high mountains, steep slopes and torrent water, the increasing impervious areas ratio in urban area is more important role for not only the increasing direct runoff volume but also the hydraulic efficiency resulting in the concentrated peak flow. Therefore, we are facing the inundation endangering the people's lives and property. All of the hydraulic engineering facilities and the flood control constructions have certain degree of protection ability. And the urban drainage systems to the storms are general designed certain criteria. If the flood volume exceeds the designed criteria, especially the heavy rain form typhoons and the concentrated short duration storms, the flood over the capacity of drainage systems will make surcharge and inundation phenomena. Thus, it is important issue and essential to understand the phenomena of urban flooding, and adopt effective measures to improve the situation caused by highly urbanized. The flood could be managed either by the temporary solution like the traditional concentrated design of hydraulic engineering facilities or the root of the problem like Low Impact Development (LID) techniques to reduce the threaten of flood. The idea of LID in the United State has been promoted over ten years. The application of LID devices include vegetative swales, rain barrels, permeable pavement, bioretention cells, rain gardens and so on. LID emphasizes on maintaining or restoring the site hydrological conditions back to predevelopment. And its strategy is combining distributed, parallel connection and small-scale devices functioning as infiltration, interception, rainwater storage or detention facilities to increase infiltration chances for runoff and lengthen the time of concentration. By this source control methods, the environmental impact could be reduced and maintained hydrological conditions of predevelopment such as surface runoff, infiltration, surface and groundwater exchange effects. The purpose of this study is combing Storm Water Management Model (referred SWMM) and 2D flooding model to simulate direct runoff, surcharge volume, peak discharge, peak time and inundation areas for 6 hydrological events. And, evaluating the effectiveness of LID for urban flood control as indicators of direct runoff, surcharge volume, peak discharge, peak time and inundation areas by several simulation scenarios. The results showed that the more application of LID to replace impervious pavement the more benefits of flood control. And the maximum benefits of LID reducing direct runoff is 60%, because of the soil has its limitation on infiltration capacity.