Taxpayer Money Spent to Prevent 'Water Bombs,' But Results Are 'Shocking': The Dismal Reality of Permeable Pavers in Seoul

00:00 Are 'permeable pavers' the solution to avoid monsoon 'water bombs'?
02:49 Is their performance being maintained?
04:25 Why are two-thirds of them 'defective'?
06:31 Why have inspections not been carried out properly?

1. Are 'permeable pavers' the solution to avoid monsoon 'water bombs'?
Hello, I am Jang Se-man, an SBS climate and environment correspondent. The monsoon season has arrived. In the past, this was a time of inconvenience due to frequent rain and high humidity. However, due to climate change, we now face extreme amounts of rainfall and massive damage that we could never have imagined. It has reached a point where this season is no longer just about inconvenience, but about enduring with anxiety. The danger is particularly high in urban areas because the ground around us is covered in either asphalt or concrete. This structure prevents rainwater from soaking into the ground. Because the soil has lost its role in absorbing rainwater, the water simply accumulates and flows, which is the reality in the urban areas where many of us live. Conversely, because the surface cannot absorb water, it cannot store it, leading to water shortages during droughts. To solve this problem of increasing impermeable surfaces, 'permeable pavers' were introduced. These are paving blocks designed to allow rainwater to pass through and drain into the soil beneath. The principle is that when the blocks are manufactured, countless microscopic holes are created to allow water to pass through the gaps.

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

In fact, when placed side-by-side with regular paving blocks, the existing blocks look smooth, while the permeable pavers appear rough with many visible gaps. How do these pavers actually perform when it rains? If you look at footage taken where these pavers are installed, you can see puddles of rainwater on regular asphalt. However, in areas with permeable pavers, water accumulation is clearly less visible. Even in experiments where water is intentionally poured, you can see it draining away quickly. Because of these advantages, the Seoul Metropolitan Government established the 'Basic Ordinance on Water Cycle Restoration and Low Impact Development' in 2015, making the use of permeable pavers mandatory. It has been over 10 years; how many have been installed? About 15% of the total sidewalk area in Seoul has been covered. Permeable pavers are 10–20% more expensive than regular blocks, and since they are replaced only when old blocks are removed for construction, only a portion has been replaced even after more than a decade.

2. Is their performance being maintained?
So, are these installed blocks actually maintaining their performance? The Seoul Institute conducted an on-site survey. They selected 30 locations in Seoul where permeable pavers had been installed for less than a year. The performance of these pavers is measured by how many millimeters of water they can absorb per second. There are currently Grade 1, 2, and 3 products. Until last year, it was required to install Grade 3 or higher products, and starting this year, the standard was strengthened to Grade 2 or higher. Grade 1 means absorbing 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 used Grade 3 products at the time of installation. However, the Seoul Institute's measurements showed that only 10 locations met the Grade 3 standard of 0.1 millimeters of absorption. 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 found to be defective.

[Park Dae-geun / Senior Research Fellow, The Seoul Institute: The results showed that about two-thirds were clogged or mostly clogged. (The performance survey results) are intended to raise awareness of the seriousness of the situation.]

3. Why are two-thirds 'defective'?
Why did this result occur? There are two possibilities. One is that the products were fine initially, but various debris and pollutants clogged the holes after installation. The second is that defective products were used from the very beginning. The Seoul Institute maintains that this survey alone is not enough to conclude which is the case. However, the paving block manufacturing industry is viewing this situation with suspicion. They question whether holes 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 suspicion. They conducted a long-term tracking study on how long the permeability of these blocks lasts. For the aforementioned Grade 3 products, the time it took to drop to the management standard—a permeability of 0.1 millimeters—was approximately 3.2 years. This means performance only dropped 3.2 years after the new products were installed. For Grade 1 products, it took 5.1 years. There are also permeable pavers installed on roads, not just sidewalks where people walk. In that case, for Grade 1 road pavers, it took 17 years for the permeability to drop to 0.1 millimeters, according to the study. Therefore, the criticism is that it does not make sense for two-thirds of them to have such poor permeability after only one year. Of course, one must consider that because the holes are created artificially, clogging due to various dust and debris over time is inevitable. That is why the current system requires performance inspections every two years.

4. Why have inspections not been carried out properly?
However, these performance maintenance inspections have not been carried out properly. Why? Because there were no appropriate testing methods. Overseas standards did not fit well when applied domestically, and bringing them into a laboratory for measurement was difficult, as it required breaking the blocks. It was only last year that the Seoul Institute developed a testing method that could be used in Korea, and through this, they released the measurement results for the 30 locations mentioned earlier. In addition, the Seoul Metropolitan Government is currently surveying the performance of 1,000 locations across the city to get a more precise grasp of the situation. The results are expected to be released around November of this year. It is essential to uncover the accurate state of the performance of the permeable pavers installed so far. Furthermore, this should serve as an opportunity to conduct a clear investigation into whether the cause of the defective products is natural clogging due to 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.