Evaluation of Levee Scouring Risk in the Middle Chikugo River Influenced by Rainfall Spatial Distribution Using d4PDF

This research assesses the relationship between rainfall spatial distribution and levee failure risks by scouring at the confluence of the Chikugo River mainstream and Kusu River. Using d4PDF large climate ensembles (10,140 years of data), the study integrated a Rainfall-Runoff-Inundation (RRI) model with iRIC Nays 2DH for 2D hydro-morphodynamic analysis.The ensembles were categorized into three groups(Main-heavy, Intermediate, and Kusu-heavy) based on rainfall centroid locations representing where the rain falls heavily for each ensemble. Results showed that the Kusu-heavy group presents the greatest risk, expanding the longitudinal range of scouring. While peak scouring in the low-water channel shifts location depending on the rainfall distribution group, the high-water channel exhibits critical scouring in a same location. This localized risk is driven by topography and sediment dynamics rather than discharge ratios, consistently threatening the same location regardless of the ensemble. Although the analyis revealed the scour risk location and mechanism, further morphodynamic data and model verificaiton will be required to utilize these findings practically, as data availability limited the full morphological validation of the iRIC model.