The Flow Field Characteristics and the Dam Notch Development in Field Overtopping Breach Experiment
堰塞壩 ； 溢頂 ； 潰決 ； 原尺寸試驗 ； 影像分析 ； PTV ； Landslide dam ； Overtopping ； breach ； large scale experiment ； Image processing ； PTV
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極端降雨事件易引致大規模崩塌與土石流事件發生，大量的土砂容易堵塞河道而形成堰塞湖，堰塞壩潰決後所釋放的洪水不僅危害下游地區居民之生命及財產安全，更顯著地改變下游河道特性，因此了解堰塞壩潰決基本特性，成為土砂災害治理工作的重要課題。 本研究使用現地堰塞壩潰決實驗，配合影像分析方法進行流場分析，將潰決歷程依照水流階梯式侵蝕現象前後區分為兩個階段。發現壩體上不同斷面位置的流速分佈具有相似性，並逐漸向上游遞移。受到水面梯度影響，上游斷面流速趨勢較下游斷面平緩。潰決歷程的兩階段中皆會發生溯源現象，溯源發展處水流寬度受側向崩塌土方影響而束縮、受高差因素影響流速增快，通洪斷面小；壩體溯源完成後因流速進入穩定，潰口發展完整，出現較大通洪斷面積，出流量快速上升。觀察整體潰決歷程，發現流速與流量變化趨勢成負相關，因此得知堰塞壩潰決過程流量變化由通洪斷面積主導。 本研究對於潰決歷程及流速在空間及時間上進行深入探討，於堰塞壩潰決流速及通洪斷面特性的分析上有相當進展，期盼未來能提供相關研究者進行參考。並對於通洪斷面形狀及水深進行初步討論，提供往後研究進行改進。
Extreme rainfall events induce landslides and debris flows and large amounts of sediment could block river channels and form dam lakes. Floods release after dam breach cause serious disasters and change channel forms for downstream areas. Therefore, understanding the basic characteristics of the dam breach is a key issue for disaster mitigation. In this study, we used the large scale dam breach experiments and the flow fields are analyzed using an image processing method. Breach process is divided into two stages according to the phenomenon of step erosion. It has been found that the different dam sections have similar velocity distributions and these velocity distributions gradually move toward the upstream. Influenced by the water surface gradient, the flow velocity of the upstream section is gentler than downstream section. The headwater erosion phenomenon occurs in the two stages during the breach. The width of water surface is affected by the collapse of the earth, and the flow velocity and the flooding area. After the completion of headwater erosion in Stage2, velocity state became stable, the development of notch was completed, and a large flood-crossing area was appeared, and the discharge was raised rapidly. Observing the overall process during the breach, it has been found that the velocity is negatively correlated with the trend of discharge. Therefore, the flow change during the breach is dominated by the flooding area. This study explores the process of breach and velocity in spatiality and temporality. There has been important progress in the analysis of the velocity profiles and the characteristics of the flood-cross section. It is expected that relevant researchers will be provided for reference in the future. A preliminary discussion on the shape and depth of the flood cross section is provided, and future research is provided for improvement.
生物農學 > 生物環境與多樣性