Long-term permeability of permeable pavement in an urban area: a case study of Seoul, South Korea.

Permeable pavement systems are a key low-impact development strategy for mitigating rainfall runoff in urban environments. However, their long-term effectiveness is often compromised by clogging from particulate matter, which progressively reduces permeability. This study evaluates long-term permeability of PPs installed at 13 sidewalk locations in Seoul, South Korea, over 38 months (May 2018-June 2021) using in-situ tests (KS F 2394). Results show that by the end of monitoring, eight sites had declined to Grade 5 (lowest classification), while five sites maintained Grade 3. According to Seoul guidelines, the minimum recommended permeability is Grade 3. These findings indicate that more than half of the sites fell below the recommended standard within 3 to 5 years of installation, highlighting the critical need for regular maintenance. The study aligns with recent research demonstrating that pressure washing can effectively restore permeability in clogged pavements. Based on these results, a guideline revision is proposed: adding a new top category (Grade 0) for superior permeability (≥1.5 mm/sec) and raising the minimum recommended permeability to Grade 2 to ensure longer-term performance before maintenance is required. Future research should develop more efficient cleaning techniques to sustain the hydrological function of existing permeable pavement installations in urban areas.