In August 2022, as a result of an extreme heavy rainfall event in Seoul, there were several casualties reported at underground houses and underground parking lots in the low-lying areas south of the Han River in Seoul. On that day, despite the severe flooding situation, a building in Gangnam successfully prevented flood damage through the installation of flood barriers, emphasizing the importance of flood barrier installation. As a response, the city of Seoul has been expanding its support for flood barrier installation. However, there are currently no established guidelines for the proper installation, operation, and management of flood barriers. Furthermore, in some residential complexes, there is a negative perception of flood barrier installation due to concerns about the potential impact on property values and being labeled as a flood-prone area. This has made it challenging to expand flood barrier installation.

In this study, we have proposed guidelines for the installation and operation of flood barriers in Seoul’s housing underground spaces, which include underground houses and underground parking lots. Additionally, we have presented a strategy for expanding flood barrier installations.

To ensure the effective operation of flood barriers during flooding incidents, it is crucial to consider the characteristics of flood-prone areas, including flood 109 Strategies and Recommendations for Expanding Flood Barrier Installations in Seoul's Underground Housing depth and the potential inflow of surface water. Flood barriers should be installed with a minimum height of at least 50 cm above the expected flood depth. In cases where flood barriers alone are not sufficient for flood defense, additional measures, such as installing flood barriers designed for securing evacuation routes or supporting the relocation of vulnerable individuals like severe disability and mobility-impaired elderly residents from underground housing to homes on higher floors, should be prioritized.

When installing flood barrier devices, factors such as the weight of the equipment, the complexity of installation, and the required time should be considered. It is advisable for a minimum of two individuals to work together during the installation of flood barriers. The appointment of a designated manager responsible for regular inspections of installation locations, flood barrier equipment, and storage areas is essential to ensure proper maintenance and operation of the flood barriers.

We conducted an analysis of areas requiring flood barrier installation and estimated the anticipated installation costs. Following the flood risk criteria and recognizing areas where flood damage is a concern, we classified regions with a relatively high likelihood of flood damage within Seoul. Within these designated areas, we assessed the current status of flood barrier installations in underground houses and underground parking lots. The results revealed a low installation rate of flood barriers, standing at just 17% and 2% for underground houses and underground parking lots, respectively. This indicates an urgent need for the expansion of flood barrier installations.

Upon examining homes and parking facilities without flood barriers in the identified areas, we estimated the installation costs based on the type of residential facility. For standalone houses, the maximum support cost for flood barrier installation was set at 2 million KRW, while for multi-unit residences, it was capped at 20 million KRW. Consequently, the total estimated cost for flood barrier installations in the identified areas amounted to 82.4 billion KRW. Additionally, the estimated cost for installing flood barriers in households with flood-vulnerable individuals, such as residents with severe disabilities or elderly individuals living alone, was approximately 5.9 billion KRW.

We have proposed proactive measures to expand flood barrier installations in Seoul’s underground housing. These measures include:

 ◦ Designating flood-prone areas or natural disaster risk improvement zones for mandatory flood barrier installations.

 ◦ Integrating flood barrier installation requirements into Seoul’s housing redevelopment projects and revising related evaluation criteria.

 ◦ Incorporating flood barrier installation and verification clauses in lease agreements for underground housing within flood-prone areas.

 ◦ Adjusting support rates for disaster relief funds (housing flood support funds) based on flood barrier installation status.

 ◦ Expanding the requirement for flood barrier installations as a condition for flood insurance coverage and eligibility for disaster relief funds.

Finally, based on the proposed guidelines and strategies for flood barrier installation in underground housing presented in this study, as well as the expansion plan for flood barrier installations, we have introduced the “Seoul City 100mm Flood Safety Plan.” This plan aims to ensure flood protection in underground housing and underground parking lots, even during heavy rainfall events with a 50-year frequency (100 mm/hr) or more severe events (120 mm/hr, 200-year frequency).