Development of a Modular Hydrologic Model for Underpass Flood Early Warning and Its Field Demonstration

This study structures the underpass flood analysis procedure into seven modules and proposes a modular hydrologic model featuring standardized interfaces that allow component substitution and simplification. Using parameters calibrated in the authors’ previous study without recalibration, repeated executions of the model at 5-minute intervals for the July 18, 2024 event at the Sangabeol underpass in Gwacheon issued a Concern-level warning at 05:35, providing an estimated lead time of 30 minutes ahead of the field-sensor record (06:05, 10 cm). Validation against field measurements is limited to this 10 cm threshold; the subsequent Caution, Alert, and Danger levels are model forecasts obtained with the same parameters. For the Taean and Naju events, which differed in magnitude and temporal distribution, the warning level likewise escalated sequentially, occurring approximately 26-27 minutes before the predicted 20 cm depth at Danger-level issuance. These results show that operationally meaningful lead time is secured even under fixed parameters. Additionally, component-level analysis indicates that the drainage system module is the primary component requiring refinement.