都會區淹水耐災策略之評估－以新北市瓦磘溝為例

Abstract

近年因全球氣候變異加劇、極端降雨事件日益頻繁，再加上都會區高人口密度及高度開發之原因，提升其水災風險度，因此對於都會區更加造成嚴重之淹水災害。本研究以都市化顯著之新北市瓦磘溝流域為例，針對都會區之特性，擬定四種耐災策略，利用地表淹水模式反映各耐災策略之保水量，並以2009年8月12日之淹水事件，驗證瓦磘溝流域之模式，藉此提升模式之準確性。 本研究所擬定之耐災策略分別為建物貯留、綠屋頂、透水舖面及生態滯洪池，利用5年及10年之重現期雨量進行淹水模式演算，探討各耐災策略之減災效益。模擬結果顯示，各策略對於水災危險度均有良好之成效，尤其以建物貯留之整體效果最為顯著；而針對調適效率而言(淹水減少面積/策略施作面積)，生態滯洪池有良好之調適效率，表示其對局部地區有良好之減災效果。對於較大之10年重現期雨量，建物貯留、綠屋頂及透水舖面能有效地降低排水渠洪峰流量，而避免發生水位溢出堤岸兩側之現象。最後，本研究將調適成果加值至水災風險地圖，結果顯示研究區境內村里經耐災策略調適後，風險有下降之現象，藉此多面向因子之風險評估，進而提升其洪災耐受度。

In recent years, extreme rainfall events become more frequent due to global climate anomaly. The flood disasters are more serious especially in metropolitan because of its high population density and excessive development. Therefore, it leads to the increment of the flood risk. This research takes Wayaogou Drainage located in New Taipei City as the study area which is highly developed and selects four adjustment strategies based on the characteristics of urban areas to analyze flood mitigation. This study evaluates the mitigation performance of these four strategies separately by using the simulated results obtained from flood inundation modeling. The flood inundation model is verified by the flood event occurred on August 12, 2009 to check the numerical accuracy. The above selected adjustment strategies are building retention, green roof, permeable pavement and ecological detention pond, respectively. Two different rainfalls (5-year and 10-year return periods) are input into the flood inundation model to analyze the benefits and limitations of these four strategies. The simulated results show that the flood area reduced after applying the adjustment strategies. Among the four strategies, building retention can decrease the most flood area. Regarding the aspect of adaptation benefits (e.g. the ratio of reduction of flood areas to adaptation areas), the strategy of the ecological detention pond is more efficient than others. It can obviously reduce flood areas in its surrounding region. For 10-year return period rainfall, the peak discharge in channels will approach to the safety value and be prevented from overbanking by applying the selected strategies, except for ecological detention pond. Eventually, the contribution of the four strategies is presented in flood risk map. Through conducting these adjustment strategies, they all descend the flood risk and then ascend the flood resilience in Wayaogou drainage.