Modeling the transport and retention of floating wreckage following alternative-fuel ship accidents: A scenario-based framework.

The increasing adoption of alternative-fuel vessels has raised concerns regarding the environmental impacts of marine accidents; however, information on the transport of accident-generated floating wreckage remains highly limited. This study developed a comprehensive scenario-based framework to evaluate the transport and retention characteristics of floating wreckage following hypothetical LNG-fueled ship accidents in the Ulsan coastal region, Republic of Korea. A total of 7000 hypothetical accident scenarios were generated by combining 70 representative accident locations with 100 randomly selected accident times in 2024. Using a validated SCHISM hydrodynamic model coupled with the OpenDrift particle-tracking framework, we identified a critical hydrodynamic transition region separating retention-dominated coastal waters from offshore transport pathways. Transport behavior varied significantly with accident location and seasonal forcing. Winter conditions produced higher offshore outflow rates, whereas summer conditions increased Local Exposure Time (LET) because coastal recirculation promoted wreckage retention. These findings demonstrate that local hydrodynamic conditions and seasonal variability are the primary controls on floating wreckage dispersion. The proposed framework provides a practical and adaptable basis for assessing the long-term environmental fate of marine wreckage and supporting strategic preparedness and recovery planning for alternative-fuel ship accidents.