低衝擊開發技術應用對於都市發展之高地排水的影響與效果 -以林口區新市鎮為例

Abstract

隨著經濟的發展，人口往都市集中使得都市快速的發展，然而都市的空間有限，都市化的過程使得不透水面積在都市區域中的比例大幅提升，造成能將雨水入滲至地表下的區域減少、地表水力效率的提升，進而使直接逕流量體的增加與洪峰量的集中，因此在都市地區發生洪水災害的機率與程度也隨之提升。為避免人口密集地區發生水災，造成生命財產安全的威脅，過去主要發展利用將地表逕流匯集後快速排出的水利設施，避免區域中未入滲的雨量蓄積而造成淹水。 然而，都市持續的發展下，更多區域為不透水面所取代，在集中降雨之暴雨或颱風來臨時，水利、防洪設施僅能提供一定程度的保護作用，而加大或增建雨水下水道管線的改善效果有限，尤其其他都會區上游之台地，都市發展的防洪策略，更不能僅是為了避免都市淹水，而將區域發展後增加的地表逕流完全排至下游，如此一來將造成人口密集區產生更大量之洪水；故了解都市排水現象，並採取有效的方法來改善因高度都市化造成之淹水現況，乃相當重要之課題。 藉由低衝擊開發(Low Impact Development，LID)技術於美國推廣大約十幾年，LID技術主要是透過源頭的管理，藉由小規模、分散式的透水、保水、滯洪設施，增加雨水入滲的潛勢、基地的保水能力與延長集流時間，以減少環境衝擊的水文地貌，或改善開發密度高的土地利用情形，期望能維持基地開發前的水文與地文條件，減少都市受洪水威脅的機率。常見的LID設施包含：透水鋪面、生態蓄流池、植生草溝、雨水貯留桶、綠屋頂及雨水花園等。 本研究藉由暴雨逕流管理模式(Storm Water Management Model，SWMM)，建立區域的排水系統模型，模擬在目前的水文地文條件下，檢視現有滯洪池的滯洪能力與形式並將其分類；此外，模擬在各水文事件下，比較「區域中設置LID綜合策略」與「區域開發後未設置 LID設施」兩種情形下之地表逕流量、洪峰流量與淹水區域，並求得其增加或削減的比率，以評估LID對於都市防洪的效益。研究結果：將區域中的滯洪池，依滯洪能力分為四類；LID設置後有一定的滯洪能力，由於土地對於洪水有一定容受度，因此降雨強度變大則LID的減洪效率有變小的趨勢，但仍能維持現有的排水情形。

Due to the global increasing population, city developments progress rapidly; on the other hand, results in the increase of impervious surface area. Sub-tropical islands like Taiwan encounters huge amounts of rainfall every year in monsoon season. Extreme rainfall not only increases direct runoff volume but also brings up the concentrated peak flow, which creates greater opportunities of flood. In order to avoid the the threat of flooding, flood control facilities are widely used in city development. However, flood control facilities have limited degrees of protection for flooding prevention. Therefore, the idea of Low Impact Development (LID) was brought up, which has been promoted by United State for over ten years. 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 . The common LID devices include permeable pavement, bioretention cells, vegetative swales, rain barrels, green roofs, rain gardens and so on. The purpose of this study is by using Storm Water Management Model (referred SWMM) to simulate direct runoff, peak discharge, peak time and inundation areas for 5 hydrological events in 15 drainage area in Linkou area of New Taipei City. 1. The detention basins will be evaluated and sorted by its ability to afford rainfall intensity. 2. Furthermore, two scenarios will be surveyed, area without LID device and setting LID devices in 15 drainage area averaged about 42% of impervious area. Effects of the two scenarios will be described and presented which is the better solution. The results show that: 1. 23 detention basins can be sorted into four groups according to the tolerance of rainfall intensity. 2. The area with LID device can offer a smaller amount of runoff and peak discharge than impervious area without LID device. The area with LID devices keeps the land use in developed area a better condition as predevelopment area.