Optimal Arrangement of Low Impact Development Facilities in An Urban Area: A Case Study of Min-Sheng Community

本研究以低衝擊開發 (Low Impact Development, LID) 技術，考量整體效益成本分析(Benefit-Cost Analysis)，建立一都市區域低衝擊開發設施最佳化配置優選模式，並進一步以臺北市民生社區作分析案例，以彰顯模式之可用性。 此一優選模式的建立首先定義益本比為目標函數，各次集水區配置面積限制、共用面積限制和模擬模式作為限制式，低衝擊開發設施透水鋪面、生態滯留單元、滲透側溝、雨水桶、植生溝、綠屋頂和樹箱等七類之配置面積及數量為決策變數，並將其公式化。接著以啟發式演算法中的模擬退火法(Simulated Annealing, SA)為求解方法，透過暴雨管理模式(Storm Water Management Model, SWMM)模擬不同重現期距在此配置下之淹水損失情形，並計算其年計成本、年計效益以及益本比。最後，當益本比計算得到最大化時，此時之配置即為都市區域低衝擊開發設施之最佳化配置。 由臺北市民生社區之案例分析優選結果顯示，導入低衝擊開發設施前後之效益，年淹水損失由2.88億元新台幣降低至2.78億元新台幣，年計效益為9.84百萬元新台幣，年計成本6.79百萬元新台幣，益本比為1.448。並且在各個重現期距暴雨之環境下，次集水區出口和下游撫遠抽水站前池的洪峰流量和延遲洪峰到達時間皆有明顯削減。此外，低重現期距之效益也較優於高重現期距。 在低衝擊開發設施配置方面，都市地區配置面積應以綠屋頂和生態滯留單元為主，雨水桶與透水鋪面為輔，其約佔總年計成本的80%。而滲透側溝和植生溝因其功用以輸水為主，減洪效益較不彰顯，故於都市地區考量減洪效益配置時較不建議使用。此外，低衝擊開發配置面積約占總面積之18%，並根據次集水區之土地利用以及待處理面積比例，考量其低衝擊開發設施配置：住宅區以綠屋頂、雨水桶和生態滯留單元配置比例較高，道路以透水鋪面配置比例較高，而綠地主要為生態滯留單元。This study establishes an optimal arrangement model for urban areas based on Low Impact Development (LID) with consideration of Benefit-Cost Analysis. This model was developed first by defining and formulating the objective function, the constraints, and decision variables. Benefit/Cost ratio was set to be the objective function. The constraints included limitation of each subcatchment area, distribution limitation of LID devices in each area, and the chosen mode of simulation. The decision variables correspond to the allocated areas and amounts of LID devices, which include porous pavements, bioretention cells, infiltration trenches, rain barrels, vegetable swales, green roofs, and tree boxes. Under the allocation, the flooding loss was simulated by Storm Water Management Model (SWMM) in different return periods and resolved with the help of Simulated Annealing (SA). The annual benefit, annual cost, and Benefit/Cost ratio (B/C ratio) were also calculated. When the B/C ration is maximized, the allocation then is the optimal arrangement of LID devices applied to an urban area. Min-Sheng Community in Taipei is exemplified for demonstration of applicability of the optimal model. On the one hand, the efficiency resulted by showing that annual flooding loss decreases from 288 million NTD to 278 million NTD after the optimization. The B/C ratio is calculated as 1.448 with annual benefit is 9.84 million NTD, and the annual cost is 6.79 million NTD. In condition of rainfalls in each return periods, the peak flows and the average delay of peak flows of Fu-Yuan Pumping Station and the subcatchments decreased significantly. Furthermore, the efficiency of low return periods is superior in contrast with which of high return periods. On the other hand, the arrangement of LIDs in urban area takes green roofs and bioretention cells as main devices, which was supplemented with rain barrels and porous pavements. These devices are 80%of the total annual cost. Since infiltration trenches, vegetable swales and tree boxes are used mainly to transport water, the performance of flood reduction is not efficient, these devices are not commended to be considered in flooding decreasing for urban areas. Moreover, arrangement area of LID devices, which accounts for about 18% total area, was considered with the land use of urban areas and the ratio of pending areas: equipping residential district with green roofs and rain barrels, setting up porous pavements, bioretention cells in road districts, and distributing green lands with bioretention units, respectively