2025 Volume 81 Issue 16 Article ID: 24-16101
In response to the increasing frequency of flood events due to climate change, the importance of flood risk information has grown. Flood risk is composed of hazard, exposure, and vulnerability. In flood inundation analysis, which evaluates hazard, the assumption that levee breaches occur when river water levels reach the design high water level (HWL) is commonly used. However, actual flood events often show that levees do not necessarily breach at HWL, and breaches due to seepage or erosion without overtopping have also been reported. For quantitative hazard evaluation, it is essential to establish levee breach conditions that reflect actual phenomena, and probabilistic evaluations are already implemented in several countries. Therefore, this study developed a fundamental breach probability evaluation model that simplifies the erosion-induced breach process. The model was applied to the Tokachi and Satsunai Rivers in eastern Hokkaido, demonstrating that the relative breach probabilities at different evaluation points correspond to the levee and external conditions input into the model.
