00:00 Permeable Pavements: A Solution to Avoid Rainy Season 'Water Bombs'?
02:49 Is Performance Being Maintained?
04:25 Two-Thirds Found 'Defective': What Is the Reason?
06:31 Why Are Inspections Not Being Conducted Properly?
1. Permeable Pavements: A Solution to Avoid Rainy Season 'Water Bombs'?
Hello, I am Jang Se-man, a climate and environment correspondent at SBS. The rainy season has arrived. In the past, this was a period 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 the rainy season is no longer just an inconvenience, but a time we must endure with anxiety. The danger is particularly high in urban areas because the ground around us is covered in asphalt or concrete. This structure prevents rainwater from seeping into the ground. In urban areas where many of us live, the soil has lost its role in absorbing rainwater because the water just accumulates and flows away. Conversely, because the surface cannot absorb or store water, these areas are inevitably prone to water shortages during droughts. To solve this problem of increasing impermeable surfaces, permeable pavements were introduced. These are sidewalk blocks designed to allow rainwater to pass through and drain into the soil beneath. The principle is that the blocks are manufactured with countless microscopic holes to allow water to pass through the gaps.
[Jo Si-hyung / Seoul Metropolitan Government Official in Charge of Permeable Pavements: Permeable pavements are playing a role in preventing urban flooding by absorbing some of the rainwater.]
In fact, if you place them side-by-side with regular sidewalk blocks, you can see that while conventional blocks have a smooth surface, permeable blocks have a rough texture with many visible gaps. How do these blocks actually perform when it rains? If you look at footage taken where permeable pavements are installed, you can see 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 intentionally sprayed, the water drains 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 pavements mandatory. It has been over 10 years; how much has been installed? About 15% of the total sidewalk area in Seoul is covered with them. Permeable blocks are 10% to 20% more expensive than regular blocks, and since they are usually replaced when old blocks are removed for construction, only a portion has been replaced even after a decade.
2. Is 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 pavements had been installed for less than a year. The performance of these blocks is measured based on how many millimeters of water they can absorb per second. Currently, there are Grade 1, 2, and 3 products. Until last year, the requirement was to install Grade 3 or higher products, and this year, the standard was strengthened to Grade 2 or higher. Here, Grade 1 means absorbing 1 millimeter or more of water per second, Grade 2 means 0.5 millimeters, and Grade 3 means 0.1 millimeters. All 30 locations had 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 performed at only 40% of the Grade 3 standard, and the remaining 2 showed no permeability at all. In summary, two-thirds of the total were effectively found to be defective.
[Park Dae-geun / Senior Research Fellow at The Seoul Institute: The results showed that about two-thirds were clogged or mostly clogged. We need to recognize the severity of this (performance survey results).]
3. Two-Thirds Found 'Defective': What Is the Reason?
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 stated that it cannot conclude which is the case based on this survey alone. However, the paving block manufacturing industry is viewing this situation with suspicion. They question whether holes would really 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. It was a long-term tracking study on how long the permeability of these blocks lasts. For the Grade 3 products mentioned earlier, it took approximately 3.2 years for the performance to drop to the management standard of 0.1 millimeters of permeability. This means performance only declined 3.2 years after the new products were installed. For Grade 1 products, it took 5.1 years. There are also permeable blocks installed on roads, not just sidewalks for pedestrians. For Grade 1 blocks used on roads, the study found that it took 17 years for permeability to drop to 0.1 millimeters. Therefore, critics point out that it does not make sense for two-thirds of them to lose their performance after just one year. Of course, this factor must be considered: because the holes are created artificially, clogging due to dust and debris over time is inevitable. That is why the current system requires performance inspections every two years.
4. Why Are Inspections Not Being Conducted Properly?
However, these performance maintenance inspections have not been conducted properly. Why? Because there were no appropriate testing methods. International standards did not fit well in Korea, and taking blocks to a laboratory for measurement was difficult, as it required breaking them. It was only last year that the Seoul Institute developed a testing method that could be used domestically, 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 permeable pavements 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 reveal the accurate state of the performance of the permeable pavements 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 | Written by Shin Hee-sook | Video by Ahn Jun-hyeok | Graphics by Yook Do-hyun | Produced by SBS Digital News
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