耦合一維下水道模式及二維有限體積漫地流模式ANUGA於都市淹水之應用

Abstract

都會區的淹水多發生於較為低窪的街道區塊或綠地公園，若以過去常用之結構網格進行模擬，雖在網格劃設上較為簡單，但如果要對街道淹水的位置有較為精細的評估，則須提高網格解析度，而在有限的地文資料以及電腦資源下較難有良好的淹水模擬評估結果。 因此，本研究以非結構三角網格進行淹水模擬評估，並在相同網格量級下提出均勻網格以及非均勻網格2種網格建置策略，前者使用大小形狀均勻之網格進行建置，後者沿著街道區塊進行建置並對網格進行加密，藉此獲得更精細的結果。另外，搭配二維漫地流模組與降雨扣減之演算模式、二維漫地流模組結合一維雨水下水道模組之交互演算模式、二維漫地流模組結合一維雨水下水道模組之特殊演算模式進行模擬，共6種組合用以評估各模式於模擬都會區淹水之差異。 本研究以臺北市文山區木柵次集水區為研究區塊，以2場短延時強降雨事件為對象進行分析，結果顯示，非均勻網格在各排水模式中所獲得之偵測率以及精確度都高於均勻網格，因此，非均勻網格設置較適用於都會區淹水模擬評估；此外，考量建物屋頂排水相較於其他排水方式在精確度上相獲得了最高的數值，由此可知為該模式較符合都會區排水機制因而最為精確。

Urban flood usually occur in low-lying street areas as well as green areas. In the past, structure mesh is often used to simulate flooding, and if we want to make precise assessment of road flooding, the high-resolution mesh must be considered. However, due to the limited geographical information and computing resource, it's difficult to obtain accurate flood simulation result. Therefore, we use unstructured meshes to build two types of mesh structure in similar quantity, homogeneous meshes and non-homogeneous meshes, and simulate by finite volume method (FVM) model ANUGA to make flooding simulation assessment. Homogeneous ones has similar mesh density in whole the study area, and non-homogeneous ones has higher resolution in road network than other areas. Besides, we compare these mesh types in (1) rainfall reduction method, which is minus estimated drainage capacity of sewer system from input rainfall data and processes in two-dimensional (2D) overland flow model (OFM), (2) interaction method, which uses manhole as discharge exchange spots between one-dimensional (1D) sewer flow model(SFM) and 2D OFM, (3) special interaction method, which is based on interaction method and allowing rainfall input sewer system directly form building roofs. In this study, we select Muzha drainage basin in Wenshan District, Taipei as the study area and choose two short duration for simulation and analysis. It shows that non-homogeneous meshes has better value of precision than homogeneous ones due to the appropriate mesh structure. Moreover, building roof drainage method has closest flooding prediction to the survey records than other method and the best precision, because it could better reflect the drainage mechanism in urban environment.