中華民國內政部建築研究所中華民國內政部建築研究所

一、研究緣起
民國107年6月20日總統華總一義字第10700066601號令修正水利法部分條文，第七章之一為「逕流分擔與出流管制」專章，要求土地與建築開發者共同分擔滯洪、蓄水責任，以提高土地整體耐淹能力。此一修法點出逕流分擔與出流管制之重要性與防洪治水觀念之轉換。
都市積淹水之因素眾多且複雜，縱然有防洪設施之建設，但一旦雨量強度過大、下游潮位過高引發潮位上溯排水系統等，排水設施亦可能渲洩不及甚至溢流。滯蓄洪設施是近期都市減洪規劃中重要設施，然可能因啟動操作之時機影響其運作效能，進而衍生都市地區存在無法排除之有害逕流造成積淹水之問題。為避免逕流疊加造成更嚴重的局部地區淹水問題，需先分析在現有防洪設施基礎下，暴雨事件造成之都市區域地表逕流量，以進一步規劃減災調適之策略以容蓄洪水避免災害。
本研究以「極端降雨引致都市洪水即時預警模式與減災調適技術整合應用研究」之研究成果為基礎，以滯蓄洪設施為中心，綜合檢討分析都市地區之現有防洪設施，如排水系統、抽水站與滯蓄洪設施，各防洪設施之運作對都市防洪機制之影響，進而探討降雨事件之都市積淹過程各滯蓄洪設施如何運作，規劃佈設臨時抽水機位置，提高淹水時抽水效率、縮短退水時間等，加強淹水時之應變能力，以發揮其較佳效能，達到減災調適之目的。
二、研究方法及過程
本研究應用「極端降雨引致都市洪水即時預警模式與減災調適技術整合應用研究」之研究成果─都市洪水即時預警模式，發展滯蓄洪設施模組並整合至都市洪水即時預警模式，以檢討分析都市地區之現有滯蓄洪設施操作與排水系統對都市減洪機制之影響，進而探討提高淹水時抽水效率、縮短退水時間等減災調適技術，加強淹水時之應變能力，以發揮其較佳效能。本研究成果應用於災中提供即時水情資訊作為相關單位研擬減災調適策略以降低洪災衝擊之參考。
三、重要發現
本研究在選定案例研究區域後，完成演算範圍之水文、地文等相關資料之蒐集，依據所蒐集之地文資料完成都市區域非結構性格網之佈置，再以蒐集之民國106年尼莎暨海棠颱風、民國107年0823豪雨與民國108年0813豪雨等3場事件降雨與潮位歷程，分別作為輸入與邊界條件，利用本研究建置之地文性淹排水模式進行降雨逕流演算分析、演算並分析案例研究地區降雨─逕流機制、進行滯蓄洪設施之優化、都市減災技術之評估、舉辦2場專家座談會，分別就本研究之2個重要議題：「滯洪設施操作與都市防洪減災策略之探討」及「都市容洪空間規劃之探討」進行討論，會議記錄詳如附錄四，將專家對於滯洪設施操作、都市防洪減災策略及都市容洪空間規劃方面之經驗與建議納入滯蓄洪優化與都市減災調適技術評估時之重要參考。本計畫成果分述如下。
(一)蒐集資料與文獻分析
本研究完成研究案例選定與資料收集，包括研究區域之水文、地文資料、滯蓄洪設施操作資料、路面淹水感測器相關資料之收集。進一步利用上述蒐集之資料完成研究區域之非結構性格網佈置，並完成地文性淹排水模式建置。
蒐集與本研究相關之國內外文獻後，依滯蓄洪設施定義與分類、滯蓄洪設施於淹水模式之模擬等進行整理分析。
(二)模式建置與演算分析
以上述資料蒐集及分析成果為基礎，本研究依演算區域內之地形地貌及土地利用情形，佈置都市非結構性演算格網，格區間選擇適當之水流方程式演算地面水流，以擬似二維流觀念建置地文性淹排水模式，測試演算民國106年尼莎暨海棠颱風、民國107年0823豪雨事件、民國108年0813豪雨事件等3場颱洪事件作為檢定與驗證案例，以完成地文性淹排水模式之建置。
模式演算成果之水位歷程與面積平均雨量組體圖比較可知，雨型與水位歷線之分布十分類似，模式模擬之峰值、發生時間與實測水位相比亦有相同趨勢，顯示模式可合理演算降雨形成之逕流歷程。由模式演算結果與水位測站實測水位資料比較可知，民國106年尼莎暨海棠颱風安順橋測站第60小時即第2峰值之後模擬水位較實測水位低很多，水位趨勢與雨量一致，第2峰值與第3峰值間降雨有間歇，模式模擬排水較實測快。民國107年0823豪雨與民國108年0813颱風2場豪雨降雨較無間歇現象，流量峰值較接近單峰形式。
研究區域於民國108年0813豪雨期間模式演算結果與淹水站13、15、28及57之實測水深歷程相符，模式演算地面積淹30公分之到達時間亦與淹水感測器測得時間相近。
演算案例地區10年與25年重現期設計暴雨事件，透過降雨事件逕流分析，可得出10年重現期一日暴雨逕流分析之最大可暫貯留空間約在第14.9小時，最大可暫貯留量約2,110萬立方公尺。25年重現期一日暴雨逕流分析之最大可暫貯留空間約在第14.7小時，最大可暫貯留量約2,090萬立方公尺。進一步進行現有滯蓄洪設施分析，比較港尾溝滯洪池與保安抽水站兩站無操作與有操作之水位歷線，可知滯蓄洪設施經操作後，10年重現期與25年重現期之設計暴雨下，左右岸淹水區域約可降低0.6公尺至0.8公尺，且淹水延時均有縮短。滯蓄洪設施入口以堰流流入與出口以抽水流出均有其降低洪峰、洪峰到達時間後延之效。
(三)滯蓄洪設施優化
以民國107年0823豪雨事件與重現期10年設計豪雨事件進行滯蓄洪設施優化操作演算，分析與探討減洪效果並規劃佈設臨時抽水機位置。
由民國107年0823豪雨事件演算結果之流量歷線與降雨歷程互相比較可知，流入淹水區域之流量歷線之形狀與降雨歷線較為相近，即直接反應降雨產生地表逕流；而流出淹水區域之流量歷線，因受地表逕流、漥蓄與滯洪池蓄洪之影響，先反應第1個較大的峰值後以一平緩多峰歷時20小時後才開始退水。於第1峰值後發生前開始抽水，抽水開始後滯洪池水位即開始下降，歷程中以豪雨尖峰過後開始退水之有無抽水之水位相差較大，滯洪池於退水開始即進行抽水機操作，可有效迅速降低滯蓄洪水位，強化滯蓄洪設施功能。
為進一步分析滯蓄洪設施優化條件，以連續2場重現期10年豪雨事件(間隔12小時)，搭配在不同延時啟動抽水機，演算水深以分析滯蓄洪設設施操作減洪效果。以水深之平均降低值分析減洪效果，結果顯示啟動抽水機的時約在洪峰過後4小時，可以有較佳的降低滯洪池水位的成效。另以演算結果之仁德區之積淹地區，研判臨時抽水機佈設位置：三爺溪排水之上游佈設1個，仁德滯洪池佈設1個，三爺溪排水下游兩岸易淹水地區佈設4個，港尾溝溪上游佈設1個，二仁溪中下游北岸之大甲里佈設3個，共10個臨時抽水機建議佈設位置。
(四)都市減災調適技術評估
初步分析仁德常淹水地區後，初擬可以研究區域內面積較大之校園綠地規劃增加約4萬立方公尺之滯蓄洪空間，並以2年重現期一日降雨事件模擬評估減洪效果，由校園水位變化可知，此一規劃於降雨歷程前4-10小時可發揮約10cm-20cm之減洪作用。進一步探討其周邊區域之水位變化，可發現水位歷線洪峰約可延遲0.5至1小時，可發揮約5cm之減洪作用。
四、主要建議事項
建議一
滯洪設施之優化操作策略：立即可行建議
主辦機關：直轄市、各縣(市)政府水利機關
協辦機關：經濟部水利署、內政部建築研究所
本年度已完成滯蓄洪設施整合減災調適技術初步研究，建議將優化滯洪設施操作應用於實務，在即時掌握颱洪期間現地水情資訊下，可以本研究之地文性淹排水模式進行滯洪設施排洪操作評估與建議，減少都市溢淹。
建議二
土地因應氣候變遷減災調適技術研究：中長期建議
主辦機關：內政部建築研究所
協辦機關：經濟部水利署、內政部營建署
都市洪水逕流除以排水系統及滯洪設施排除外，土地亦需配合遲滯洪水，透過水理演算分析淹水區域，進一步藉由土地使用之規劃，將位於淹水風險較高區域之土地規劃為承洪或滯洪區，以提升都市耐洪減災能力，降低淹水損失。 

Background and objectives
The causes of inundation in urban areas were numerous and complex. Even though there were flood mitigation facilities, once the rainfall intensity and the downstream tidal level were exceedingly high, the flood in drainage could not be drained in time or even overflow. Detention pond was an important flood mitigation facility in recent years. However, the detention efficiency might be affected by the timing of the operation and harmful runoff that cannot be drained caused flooding in the urban areas. In order to avoid the problem of flooding in the local area caused by the superposition of runoff, it was necessary to analyze the surface runoff of the urban areas caused by the storm events on the basis of the current flood mitigation facilities.
Method and approach
Based on the research results from the previous project, “Integrated Applications of the Implementation Model of Timely Alarming as well as the Innovative Technology of Disaster Reduction and Adaption for Urban Flooding Induced by Extreme Rainfall Events”, the simulation of detention ponds have been considered and integrated into an urban real-time predicted inundation model. The model could be applied to comprehensive review and analyze current flood mitigation facilities in urban areas, such as drainage systems, pumping stations, and detention ponds, the effect of the operation of various flood mitigation facilities on urban flood mitigation mechanisms. Furthermore, how the various detention ponds operating, planning the location of mobile pumping stations, improving the pumping efficiency during flooding, and reducing the duration of flood recession during the storm events could be more effective and improve the disaster response ability to achieve the purpose of disaster mitigation and mitigation.
Main results
After choosing the study area, Rende District, hydrologic and physiographic data are collected and compacted. The computational cells are automatically generated in accordance with physiographic data such as terrain, landscape and drainage network. The Physiographic drainage-inundation model (the PHD model) is then is applied to simulate the rainfall-runoff scenarios for two typhoon events, Typhoon Nesat in 2017 and two extremely heavy rainfall events, 0823 rainfall event in 2018 and 0813 rainfall event in 2019. The effect of rainfall-runoff in the study area were analyzed. Plan the optimization of detention facilities and evaluation of urban disaster reduction technologies. The two expert forums for two important issues of this study, “the discussion of flood detention facilities operation and flood mitigation and disaster reduction strategies in urban area” and “the discussion of urban flood detention space planning”. The suggestions from the two expert forums are considered as important references of planning flood detention facilities operation, flood mitigation and adaption strategies in urban area.
The main results obtained from this study can be summarized as follows:
1.Reviewing relevant literatures
This study completed the selection of research cases and data collection, including the hydrology, geography data, operation data of detention facilities, and the collection of relevant data of “instant flood water level sensors”. Further use the collected data to complete the non-structural cells of the study area and complete the PHD model.
After collecting domestic and foreign literature related to this research, it includes the definition and classification of detention pond and how the detiontion pond operation be considered in the inundation model.
2.Developing the PHD model, simulation, and analysis
Based on the above data collection and analysis results, this study arranges the urban non-structural computational cells according to the terrain and land use in the study area, and selects the appropriate water flow equation to calculate the surface runoff. The establishment of the PHD model was carried out to test the calculus of Typhoon Nesat in 2017, extremely heavy rainfall events 0823 in 2018 and 0813 in 2019 as a verification case. The relationship of the inflow, outflow and the storage in the study area are analyzed. Select the relevant rainfall events and collect relevant rainfall forecast data, and apply the PHD model to calculate the real-time rainfall-runoff, and obtain the inundated depth and area.
This study has compared the water level between the simulated and measured results of the typhoon and rainfall events. hese results showes a good agreement in the peak value of water level, and the PHD model can reasonably calculate the runoff.
3.Optimization of detention facilities and Integration of real-time prediction model and mitigation and adaption technologies
Based on the 0823 heavy rain event in 2017 and the design heavy rain event in the 10-year return period, the operation optimization evaluation of flood detention facilities was analyzed, the effect of flood reduction was analyzed, and the location of mobile pumping stations was planned.
Analyze the optimal conditions of the detention facilities. Based on two consecutive 10-year heavy rain events (with an interval of 12 hours), and start pumping at different delays, calculate the water depth to analyze the flood reduction effect of the detention facilities. Analysis of the flood reduction effect based on the average reduction of water depth, the results show that when the pumping is started about 4 hours after the flood peak, the effect of lowering the water level of the detention pond can be better. In addition, based on the calculation results, in the flooded area of Rende District, there are 10 mobile pumping station locations are suggested.
4.Evaluation of flood disaster mitigation and adaption technologies in urban area
After preliminary analysis of the flooded area in Rende District, it is initially planned that the campus space in the area can be increased by about 40,000 m3 of flood detention storage, and the flood mitigation will be evaluated by a 24-hr rainfall event simulation of the 2-year return period. The effect can be seen from the change of the campus water level. This plan can exert a flood mitigation effect of about 10cm-20cm 4-10 hours before the rainfall course. Further exploring the changes of the water level in the surrounding area, it can be found that the flood peak of the water level can be delayed by about 0.5 to 1 hour, and it can exert a flood mitigation effect of about 5 cm.
Major suggestions
This study proposes one short-term strategy and one long-term strategy as follows:
For municipalities and county government （short-term strategy）
A preliminary study on the adaptation and mitigation technologies of detention pond has been completed. It is suggested that the optimized operation of detention facilities can be applied in the field. The suggestions of optimized operation of detention facilities can be analyzed and evaluated by the PHD model during the flood events. 
For CPAMI（long-term strategy）
Besides drainage and detention system, land are also utilized to drain or detent the runoff in urban area. Through hydraulic routing to analyze the flooded area, and further through the land use planning, the land located in the area with higher flood risk will be planned to flood resilience area to improve urban flood resilience, disaster reduction.