DEVELOPMENT OF A HAZARD ASSESSMENT APPROACH BASED ON AN INTEGRATED MODEL FOR LARGE WOODY DEBRIS DISCHARGE IN DAM WATERSHEDS

Abstract

This study proposes a physically based framework for assessing the hazard of large woody debris (LWD) discharge in dam watersheds under extreme rainfall conditions. The method integrates rainfall return-level analysis, landslide-induced LWD recruitment modeling, and discharge simulation using a double storage function with the lumped hydrological method at a watershed scale. It was applied to five representative dam watersheds in Japan to simulate the potential minimum, maximum, and expected LWD discharge volumes under varying rainfall return periods. The results demonstrate that the framework effectively captures the variability in discharge responses across sites and identifies dam-specific rainfall thresholds for potential LWD discharge. Particularly, the use of expected initial storage conditions significantly improves the reliability of hazard estimation. The observed LWD discharge records were consistently bound by the simulated discharge ranges, validating the model's applicability. In contrast to traditional observation-based approaches, this framework enables estimation of low-frequency hazards. It offers a practical tool for risk-informed reservoir management and indicates the importance of integrating physical processes in LWD hazard prediction. These findings contribute to understanding inter-site differences in LWD storage and transport behavior, enabling more proactive hazard mitigation planning under increasing extreme weather events.