A forecasting system of water elevations around Taiwan： Studies on Numerical Modeling of Storm Surges and Grid Generation in CoastalWaters around Taiwan (III)

一、總計畫： 「台灣環島海岸水位預報系統之建立」為三年期整合型計畫，整 合之構想是以台灣環島（包括澎湖、金門、馬祖等各離島）海岸水位 之預報系統建立為主題，分為四個主要的部分，包含台灣環島天文潮 汐預報模式、台灣環島暴潮預報模式、數值網格產生法研究以及台灣 環島海岸水位預報資訊系統建立。其主要目的在結合海象及海岸工程 之專精研究人員，促成學術界專業研究人員之積極參與，希能儘早完 成國內海岸溢淹預警作業系統，以早日發揮海岸溢淹災害防治功能。 本計畫為「海岸環島海岸水位預報系統之建立」整合型計畫之總 計畫，主要負責海岸水位模擬示範區之選定(在環島水位計算完成 後)，共用資料之蒐集與格式制定建檔，每年度除擔任各計畫協調工 作與資料相互引用事宜，以及現場調查支援問題，及現場看察工作 外，並召開3 至4 次期中檢討會以廣集交換計畫執行心得與需求，了 解各計畫之進度，以期確切達成計畫目標與進度。 本計畫的研究成果包括：(1)潮汐半日型主要分潮的調和常數及 潮流橢圓計算；(2)邊界元素數值計算方法中關於奇異性問題之解 析；(3)運用對數學奇異性與幾何奇異性的研究成果，探討其對邊界 符合網格系統產生的影響。同時，根據複變函數的特性，研究出其進 行複變轉換時的角度限制式；(4)小區域(單連通)以及大區域(複連通) 網格之建立；(5)完成整體地理資訊系統規劃以及初步系統建置；(6) 建立於地理資訊系統可供查詢之現場觀測資料分析結果。 一、子計畫： 本計畫為三年期整合計畫「台灣環島海岸水位預報系統之建立」 之子計畫之一，其研究目的在發展台灣本土的暴潮及溢淹預測模式， 期能降低每年颱風侵犯台灣時淹水所造成生命財產上的損失。同時， 配合總計畫，提供暴潮數值計算以及建立邊界符合數值網格予另兩個 子計畫計算所需。本研究除了引進美國聯邦緊急事故處理局發展出的 暴潮預測模式-----FEMA 暴潮模式之外，並藉由探討邊界元素法在奇 異性問題上的理論基礎，建立並改善原網格系統為邊界符合座標系 統；另外，也進一步改善FEMA 模式數值計算方法以增加計算效率 及穩定性。 模式發展初期以數值正交網格之建立、應用改良為主，中期將以 整合正交網格與新模式以及驗證為主，而在末期時並考慮天文潮位之 變化，驗證曲線座標系統之新模式。至於風場模式之修正則將於研究 後期暫以氣象局預報的大區域風場代替移動的圓形風場模式，同時考 量背景氣壓來模擬，待他日氣象界發展出較佳的風場模式時再加以改 良應用。 本模式之發展預期將可提供沿岸暴潮，沿岸河川水位，暴潮溢淹 範圍等預測之所需，乃至進一步建立台灣溢淹區洪災預警及疏散管理 系統。其並可做為本國沿海海岸後退線劃定、洪水保險等之依據。1.Main program: The object of this proposal is to form an integrated research group to make efforts in establishing a forecasting system of water elevations around Taiwan. It includes four components, namely, study of tidal prediction model on seas surrounding Taiwan, numerical modeling of studies on storm surge in coastal waters around Taiwan, numerical modeling of studies on grid generation technology in coastal waters around Taiwan, and studies on an information system of coastal water elevation around Taiwan. This integrated program is to be completed in period of three years. The team of several researchers will devote themselves to the works of numerical modeling, database establishment, and in-site investigations of coastal water elevations around Taiwan. The final goal is the establishment of a predictive and warning system for coastal floods around Taiwan. This integrated project will make a selection of main regions suffered from coastal flooding after water elevations around Taiwan are obtained. Common data format, file system, and in-site field investigations is arranged throughout this integrated research. Three to four progress meetings was conducted during the passed research period to exchange research results and to share experiences in order to achieve the goal of each individual sub-project. The study results of this year include: (1) the harmonic constants associate with the current ellipse of the principle constituents of semidiurnal tide are solved on coast and seas around Taiwan, (2) solving singularity problem of BEM and the establishment of the formulation for extending its application to multi-connected regions, (3) the computing of astronomic tide and storm surge around Taiwan, (4) the establishing of small-area (simple connected) boundary-fitted orthogonal grid system and large-area (multiply-connected) boundary-fitted orthogonal grid system, (5) completing the first-stage arrangement of Geographic Information System, and (6) in-site data associated with the data analysis can be found in GIS. 2.Sub-program: This study is a sub-study of the integrated research program “A forecastingsystem of water elevations around Taiwan”. The main purpose of this study is to develop a new storm surge model by considering the local boundary effects. And the success of this model is expected to reduce losses of life and property caused by storm surges. The other purpose of this study is to establish and offer the boundary-fitted orthogonal grid systems for another two sub-studies of this program. The study first introduces the FEMA storm surge model developed by the Federal Emergency Management Agency, U. S. A., and further improves the model theoretically and numerically by replacing the original grid system with the boundary-fitted grid system. Meanwhile, newer viewpoints about the singularity problems in BIEM are discussed. Finally, a new numerical scheme is established in this storm surge model to improve the computational efficiency and stability. In the first stage of the development of this new storm surge model, the principle work is to improve the boundary-fitted coordinate system. In the second stage, the main work is to combine the FEMAmodel with the orthogonal coordinate grid system. In the last stage, variation of the astronomic tide will be included and the verifications and validations of the new model with curvilinear coordinate system will be made. The development of this model will meet the needs of the coastal storm surge prediction, coastal river water level prediction, and coastal flooding prediction. Moreover, this study can be taken as the base of the inundation prediction and evacuation management system for coastal flooding areas of Taiwan. Also, the development of this model can provide as guidelines of the setback line and flooding insurance