| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 107 === 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.
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