以數值模擬評估自然解方在河道防災與 生態保育效益——以港口溪為例

Abstract

台灣溪流多為坡陡湍急的河道，為了有效抑制河床下切與侵蝕，傳統上多採用固床工等工程手法來進行治水防災。然而，這類剛性結構雖有助於土地安全，卻可能對河川生態造成干擾。為了在防災與生態保育之間取得平衡，現今逐漸導入自然解方（Nature-based Solutions, NbS）來改善傳統工程手法，以兼顧土地安全與生態永續。 為進一步探討自然解方在河川整治上的成效，以港口溪為案例進行分析。港口溪同樣具有坡陡湍急的特性，且長期受到侵蝕與下切影響，對周邊土地安全構成威脅。為評估不同降雨情境下河道的變化，本研究運用HEC-RAS水理數值模擬軟體，針對基流量及2年、10年、25年、50年與100年重現期洪水進行模擬分析。透過模擬結果，將比較整治前後河道在不同重現期洪水下的水位變化、流速分佈及可能的溢淹範圍，以評估自然解方對河道穩定性及防災效益的影響，並為未來類似河川治理提供參考依據。 本研究針對豐富生態資源港口溪整治前後的環境變化進行分析，評估自然解方在河川治理中的應用成效。透過HEC-RAS模擬不同重現期洪水情境下的水理變化，進一步結合生物棲息地指標（Habitat Suitability Index, HSI）進行生態面向之評估，結合NbS全球28項指標進行評分，從生態系統健康、水文功能、土地安全與社會效益等面向，全面檢視整治措施對河道環境的影響。根據評分結果，提出具體的後續改善建議，以進一步提升防災效能與生態保育成果。本研究藉此驗證自然解方的可行性與成效，為未來類似河川整治提供參考依據。

Taiwan's rivers are mostly characterized by steep gradients and rapid flows. To effectively prevent riverbed incision and erosion, traditional engineering approaches such as grade control structures have long been adopted for flood prevention and river management. However, while these rigid structures contribute to land safety, they can also disrupt riverine ecosystems. In pursuit of a balance between disaster prevention and ecological conservation, Nature-based Solutions (NbS) are increasingly being introduced to improve conventional engineering practices, aiming to achieve both land security and ecological sustainability. To further explore the effectiveness of NbS in river restoration, this study takes the Gangkou Creek as a case study. Gangkou Creek similarly exhibits steep and swift-flowing characteristics and has long been affected by erosion and incision, posing threats to surrounding land safety. To assess river channel responses under various rainfall scenarios, this study employs the HEC-RAS hydraulic modeling software to simulate baseflow conditions as well as flood events corresponding to return periods of 2, 10, 25, 50, and 100 years. The simulation results are used to compare pre- and post-restoration changes in water levels, velocity distributions, and potential inundation extents under different flood return periods. This enables an evaluation of the impact of NbS on channel stability and disaster mitigation, providing valuable reference for similar future river management efforts. Focusing on the ecologically rich Gangkou Creek, this study analyzes environmental changes before and after river restoration to assess the effectiveness of NbS in river management. By simulating hydraulic conditions under various flood scenarios using HEC-RAS and integrating the Habitat Suitability Index (HSI) for ecological assessment, the study further incorporates the 28 global NbS indicators to perform a comprehensive evaluation. These indicators cover ecosystem health, hydrological functions, land safety, and social benefits. Based on the assessment results, the study proposes specific recommendations for further improvement, aiming to enhance disaster resilience and ecological conservation outcomes. Through this approach, the feasibility and effectiveness of NbS are verified, offering a reference for future river restoration projects.