Downtown Seoul near Gangnam Station could flood 1 meter deep in extreme rainfall, study finds

Rainfall exceeding 100 millimeters per hour could flood downtown streets near Gangnam Station in Seoul to depths of up to 1 meter, according to new research.

The Korea Institute of Civil Engineering and Building Technology said Wednesday that urban flood simulations and full-scale hydraulic experiments conducted on the area around Gangnam Station showed that rainfall of 100 millimeters per hour or more — surpassing the capacity of existing drainage infrastructure — is likely to cause inundation reaching up to 1 meter.

The research is part of an ongoing effort to develop urban flood forecasting and response technology to get ahead of the increasingly frequent localized downpours driven by climate change. Researchers combined numerical modeling that reflected the characteristics of actual roads and drainage systems with full-scale hydraulic experiments at the River Experiment Center in Andong to verify how urban flooding develops and spreads.

The research team built a numerical model incorporating the terrain of the Banpocheon basin, stormwater pipe networks, longitudinal and cross-sectional road gradients, and key drainage infrastructure including storm drains. Researchers simulated rainfall and runoff conditions on a test section representing the Gangnam Station intersection — replicating actual roads and drainage facilities — and analyzed road overflow, the drainage capacity of storm drains, and the progression of flooding and rising water depths. The analysis found that rainfall of 100 millimeters per hour exceeds the limits of existing drainage capacity, producing inundation ranging from several tens of centimeters to a maximum of 1 meter. Similar results were confirmed in full-scale hydraulic experiments at the urban flood pilot facility at the River Experiment Center in Andong, validating the reliability of the simulation findings.

The findings could be used to improve the accuracy of urban flood early warning systems and to manage flood-prone areas before disasters strike. They are also expected to serve as empirical data for improving design and operational standards for urban drainage infrastructure, including stormwater pipe networks, storm drains and retention facilities.

The research team plans to expand experiments covering a wider range of rainfall conditions and drainage operation scenarios, and to advance digital twin-based urban flood forecasting technology by linking numerical models with field observation data. The goal is to rapidly predict the expected extent and depth of flooding during extreme rainfall events and to propose tailored urban flood response measures that reflect local conditions.

Park Seon-gyu, president of the Korea Institute of Civil Engineering and Building Technology, said the risk of urban flooding that exceeds the capacity of existing drainage infrastructure is growing as the likelihood of extreme rainfall of around 100 millimeters per hour increases due to climate change. "This research is significant in that it has enhanced the reliability of urban flood forecasting technology through cross-validation using computer simulation and full-scale experiments," he said.