集水區水砂災害分析與調適策略研擬-以港口溪集水區為例

Abstract

臺灣位於歐亞板塊及菲律賓海板塊的交界帶上，板塊之間的運動造成了臺灣地勢多呈現坡陡流急，加上颱風等短延時強降雨的事件，使許多地區淹水及土砂災害頻繁發生。對此，本研究將屏東縣港口溪集水區作為研究區域，透過二維水理及輸砂模式、現地勘查、統整當地居民及相關利害關係人之意見等方式，分析整個集水區所面臨的問題，並找出相對應的調適策略。 常用於分析集水區之二維水理及輸砂模式有HEC-RAS 2D、SRH-2D、FLO-2D、CCHE-2D等，綜合考量下選擇使用HEC-RAS 2D作為本研究分析之二維水理及輸砂模式，透過HEC-RAS 2D模擬在集水區的淹水及土砂災害，並利用歷史致災資料以及政府單位先前在此區域的治理規劃報告作為模式的驗證。經過驗證後，證實透過二維水理及輸砂模式分析所得出的結果有一定的可信度，再透過其結果設計出對應的調適策略。 水砂溢淹區顧名思義為讓水及土砂漫淹之區域，不同於滯洪池，水砂溢淹區的設計目標不在於延緩洪峰或減少保全對象之淹水面積等，其目標之一為利用劃定區域之面積決定土地持有者的補償費用，減少政府單位因水砂災害導致堤防等工程設施破損時，所需撥款作為修復設施之花費，進而達到節省經費以及生態友善之雙贏局面。 在眾多模擬土石流影響範圍的模式中，同樣選擇利用HEC-RAS 2D進行模擬，除了方便與先前模擬淹水之結果進行比對之外，HEC-RAS 2D之土石流模組相較於其他模擬工具，能夠以較短的時間模擬較大的範圍。將土石流的模擬結果與歷史災害等資料進行驗證後，利用模擬之土石流影響範圍檢視現有土石流避難路線及避難所之合適性。結果顯示在港口溪下游左岸靠近出海口有部分區域之避難路線經過土石流影響範圍，然而目前無更加合適之避難所，故此處民眾在進行避難時需更加留意，後續也會常是利用模擬結果與政府單位商討其他解決方案。

Taiwan is located at the boundary between the Philippine Sea Plate and the Eurasian Plate. The movement between these plates results in Taiwan’s terrain being characterized by steep slopes and high river gradients. Combined with short-duration heavy rainfall events such as typhoons, many areas frequently experience flooding and debits flow disasters. This study focuses on the Gangkou River watershed in Pingtung County as the research area. By using a two-dimensional hydrological and sediment model, on-site explorations, and consolidating the opinions of local residents and relevant stakeholders, the study analyzes the issues faced by the entire watershed and identifies corresponding adaptation strategies. Commonly used two-dimensional hydrological and sediment models for watershed analysis include HEC-RAS 2D, SRH-2D, FLO-2D, and CCHE-2D. After comprehensive consideration, HEC-RAS 2D was selected as the two-dimensional hydrological and sediment model for this study. HEC-RAS 2D was used to simulate flooding and debris flow disasters in the watershed, and historical disaster data, as well as previous governance planning reports from government agencies, were utilized to validate the model. After validation, it was confirmed that the results obtained through the two-dimensional hydrological and sediment model analysis are reasonably reliable. Based on these results, appropriate adaptation strategies were designed. One adaptation strategy is the flood-prone area. As the name suggests, a flood-prone area is a region submerged by water. Unlike detention basins, flood-prone areas go not significantly delay peak flows or reduce the flooding extent of protected area. Their primary function is to determine the compensation fees for landowners based on the designated area, thereby reducing the funds required for repairing engineering structures such as levees damaged by water and sediment disasters. This approach aims to achieve a cost-saving and ecologically friendly win-win situation. Among the various models for simulating the impact area of debris flows, HEC-RAS 2D was also chosen for this study. This allows for easy comparison with the previous flood simulation results. The debris flow model of HEC-RAS 2D, compared to other models, and simulate larger areas in a shorter time. After verifying the simulated debris flow impact area with historical disaster date, the suitability of existing debris flow evacuation locations and routes was examined. The results indicate that the evacuation route on the loft bank of the downstream Gangkou River near the estuary passes through the debris flow impact area. However, there are currently no more suitable shelters. Therefore, residents need to be extra cautious during evacuation. Future efforts will involve using the simulation results to discuss other solutions with government agencies.