FLOOD INUNDATION ANALYSES AND THREE-DIMENSIONAL HAZARD MAPPING APPROACHES FOR SMALL-SIZED RIVERS

Abstract

As global warming accelerates, the frequency and severity of heavy rainfall events have increased dramatically. Although a range of mitigation strategies exists, disaster-management specialists consistently emphasize that evacuation remains the most effective means of protecting human life. Accordingly, accurate and reliable flood-inundation information is essential for enabling timely and effective evacuations. In Japan, flood hazard maps grounded in detailed inundation analyses have been developed, disseminated, and widely utilized for major river basins. However, in small river basins, flood behavior is often influenced by backwater effects and runoff interactions with larger downstream rivers, and the development of comprehensive watershed databases has lagged. Consequently, high-precision flood-inundation analyses are difficult to perform, and reliable hazard maps are frequently lacking. In this study, we employ the iRIC (International River Interface Cooperative) model to analyze the hydraulic behavior of small river basins and to generate detailed three-dimensional hazard maps. Validation of the simulation results and the derived hazard maps confirms their reliability. The proposed methodology for flood-inundation analysis and hazard-map development is expected to provide a practical and effective framework for supporting evacuation planning and reducing casualties during flood events.