During the torrential rain in Nagoya on September 8, 2026, flooding brought train service to a halt, leaving many people stranded and unable to return home. I, too, was temporarily unable to go home because the subway had stopped, but I walked to Nagoya Station and, though it was late at night, managed to get home safely. To be honest, I had braced myself for the possibility of having to spend the night at the office, but I was impressed by how quickly service was restored—it made me realize just how much progress has been made in flood control measures in Aichi Prefecture since the 2000 Tokai Heavy Rains.
In urban areas, flood control measures are being implemented that involve temporarily storing rainwater—which the sewer system alone can no longer handle—in underground reservoirs and gradually releasing it once the peak rainfall has passed.
One such rainwater retention and infiltration technology is Sekisui Chemical’s Cross Wave Method. In this method, corrugated plastic blocks are stacked at right angles to one another and buried, creating a space underground with a high void ratio (approximately 95%). This allows rainwater to be temporarily stored. This method has become widespread throughout Japan, and it is reported to have a cumulative storage capacity of 3.9 million ㎥ nationwide.
A search on J PlatPat revealed that Sekisui Chemical Co., Ltd. holds nine active patents with “rainwater storage” included in the invention title.
I recalled that flood control work involving rainwater storage had been underway at a local children’s park for about a year, which made me realize once again the importance of infrastructure technology. (Marron)
Sekisui Chemical Co., Ltd. website on CrossWave (Japanese only): https://sekisui-cw.co.jp/