AFTER 8 SPECIAL: Concerns Over This Summer's Monsoon Season... Are 'Defective' Permeable Blocks Failing to Prevent Floods?

1. The Monsoon Season: Does 'This' Pavement Help Drain Water?
The monsoon season has arrived. In the past, this period was mainly associated with the inconvenience of frequent rain and high humidity. However, due to climate change, we now face extreme downpours and massive damage that turn this season into a time of anxiety rather than mere inconvenience. Urban areas are particularly vulnerable because the ground around us is covered in asphalt or concrete. This structure prevents rainwater from seeping into the ground, meaning the soil loses its ability to absorb water. Instead, rain accumulates and flows on the surface. Conversely, because the ground cannot absorb or store water, these areas are also prone to water shortages during droughts. To solve this problem of increasing impermeable surfaces, permeable blocks were introduced. These are sidewalk blocks designed to allow rainwater to pass through and drain into the soil below. The principle is simple: the blocks are manufactured with countless microscopic pores that allow water to escape.

[Interview: Jo Si-hyung / Official in charge of permeable blocks, Seoul Metropolitan Government: Permeable blocks play a role in preventing urban flood damage by absorbing some of the rainwater.]

While conventional blocks have a smooth surface, permeable blocks are rough and have many visible gaps. How do they actually perform when it rains? Footage taken in areas where these blocks are installed shows that while regular asphalt has puddles of water here and there, areas with permeable blocks show significantly less water accumulation. Even in experiments where water is sprayed intentionally, it drains quickly. Due to these advantages, the Seoul Metropolitan Government enacted the Basic Ordinance on Water Cycle Restoration and Low Impact Development in 2015, making the use of permeable blocks mandatory. It has been over 10 years since then, but how much has been installed? About 15% of all sidewalk areas in Seoul are covered with them. Permeable blocks are 10 to 20% more expensive than regular blocks, and since they are replaced only when old blocks are removed for construction, only a portion of the city has been upgraded even after a decade.

2. Survey Results: Two-Thirds Are Defective?
So, are these installed blocks actually maintaining their performance? The Seoul Institute conducted a field survey. They selected 30 locations in Seoul where permeable blocks had been installed for less than one year. Permeable block performance is measured by how many millimeters of water it can absorb per second, and there are currently Grade 1, 2, and 3 products. Until last year, Grade 3 or higher products were required, but the standard was strengthened to Grade 2 or higher starting this year. Grade 1 absorbs 1 millimeter or more per second, Grade 2 absorbs 0.5 millimeters per second, and Grade 3 absorbs 0.1 millimeters per second. All 30 locations were installed using Grade 3 products. However, the Seoul Institute's measurements showed that only 10 locations met the Grade 3 standard of 0.1 millimeters. Another 18 locations showed only 40% of the Grade 3 performance, and the remaining 2 locations showed no permeability at all. In summary, two-thirds of the total were effectively judged to be defective.

[Interview: Park Dae-geun / Senior Research Fellow, The Seoul Institute: The results showed that about two-thirds were either clogged or mostly clogged. We need to recognize the seriousness of these findings.]

3. Why Did This Happen?
Why did this happen? There are two possibilities. One is that the products were fine initially, but foreign substances and pollutants clogged the pores after installation. The second is that defective products were used from the very beginning. The Seoul Institute states that it cannot conclude which is the case based on this survey alone. However, the block manufacturing industry is viewing this situation with suspicion. They question whether the pores could have become clogged in less than a year if the products had been normal to begin with. In fact, another study by the Seoul Institute supports this doubt. They conducted a long-term tracking survey on how long the permeability of these blocks lasts. For the aforementioned Grade 3 products, it took approximately 3.2 years for the performance to drop to the management standard of 0.1 millimeters. In other words, the performance only declined after 3.2 years of use. For Grade 1 products, it took 5.1 years. There are also permeable blocks installed on roads, not just sidewalks. In the case of Grade 1 blocks for roads, it took 17 years for the permeability to drop to 0.1 millimeters. Therefore, critics point out that it does not make sense for two-thirds of the blocks to lose their performance after only one year. Of course, it must be taken into account that because the pores are artificially created, clogging due to dust and foreign substances is inevitable over time. That is why the current system requires performance inspections every two years.

4. Lack of Proper Inspection Methods?
However, these performance maintenance inspections have not been carried out properly. Why? Because there were no suitable inspection methods. Applying international standards domestically did not work well, and measuring them in a laboratory was difficult because it often required breaking the blocks. It was only last year that the Seoul Institute developed an inspection method that could be used in Korea, and they used it to produce the measurement results for the 30 locations mentioned earlier. Furthermore, the Seoul Metropolitan Government is currently surveying the performance of permeable blocks at 1,000 locations across the city for a more precise assessment. The results are expected to be released around November of this year. It is essential to uncover the accurate state of the permeable blocks installed so far, and this incident should serve as an opportunity to clearly investigate whether the cause of the defective products is natural aging after installation or if defective products were installed from the start.

Reported by Jang Se-man | Produced by Shin Hee-sook | Video by Ahn Jun-hyeok | Graphics by Yook Do-hyun | Produced by SBS Digital News
※ Please note: This article was translated by AI and may contain errors.