Tokyo's Underground Temple - Tunnels That Protect Tokyo From Floods

Hey guys, welcome back to another video. Today we have come to Kasukabe in Saitama prefecture to see one of the largest underground water facilities in the world. Basically, it's an enormous underground tunnel that's built around 20 kilometers north of Tokyo to prevent flooding from one of the many rivers that runs through the city. So Yasu, I heard this place was kind of famous. It'd been featured in lots of like manga and anime, right? Yeah, at least I remember it appeared on Tokyo Ghoul at one of the decisive battles. Oh wow. So yeah, I'm looking forward to seeing it. Sounds kind of epic. Maybe we can have a decisive battle ourselves. Well, our tour starts in about 10 minutes, so we need to get going. Let's go. The Greater Tokyo Area, which consists of central Tokyo as well as the prefectures of Kanagawa, Chiba and Saitama, is built on the Kanto Plain, Japan's largest area of flatland at 17,000 kilometers and is intersected by many small rivers, making it especially prone to flooding. With Tokyo's rapid urbanization, the area is now home to over 38 million people and uncountable trillions of yen in property and business value. So it goes without saying that flood prevention is a big priority for the Japanese government. In 1993, construction began on a 230 billion yen project that would take around 13 years to complete. We're up in Saitama at the moment. So if anyone knows Saitama, it's pretty just like plain. It's a very residential area. But a lot of the big rivers that come through Tokyo, they kind of start up in the north. And this one is actually next to the Edo River, which by the time it gets to Tokyo, it gets quite big. So, you know, the plant needs to be upstream to prevent flooding, you know, in the more populated area. After beginning our descent down into the main chamber, the first thing we notice is the immediate drop in temperature from the toasty 34 degrees outside to what felt like around 17 degrees by the time we'd reached the bottom. The tour takes you into the heart of the Shuto-ken Gaikaku Hosudo, or Metropolitan Area Outer Underground Discharge Channel in English. It's a mouthful in both languages, which is why it's often abbreviated to GCANS for short. So what do you think about these gigantic pillars? They're certainly gigantic. It's almost like overwhelming. They're just too big. But apparently they're 18 meters tall, right? In this one chamber, there's 59 of them supporting the weight of the ceiling above us. So they can hold a colossal amount of water, around 13 billion gallons. So it's pretty crazy. But I think until you actually come in here, you can't quite understand the size of it. It's just, it's overwhelming. The main discharge tank certainly is colossal, measuring 177 meters long and 78 meters wide. The 59 pillars that support the roof weigh 500 tons each. It's also not hard to see why this structure is referred to by many as Chika Shinden, which means the underground temple, as it has a striking resemblance to the Greek Parthenon. This area is just the final stage though, as there are also five other silos along the chain that collect water from the Otoshi Furutone, Komatsu, Kurumatsu and Naka rivers. Each of these silos is approximately 70 meters deep with a diameter of around 30 meters. That's enough space to hide the Statue of Liberty in, or even a space shuttle. At maximum capacity, the system can handle up to 670,000 cubic meters of water. And in order to offload this into the Edogawa River quickly and efficiently, this facility is equipped with four incredibly powerful 14,000 horsepower pumps, which can discharge water at up to 200 cubic meters per second. That's fast enough to drain an Olympic-sized swimming pool in only 12 seconds. So I hear this tunnel overflows only seven times a year, but it appears quite often on the media such as filming for the TV shows, movies or music videos. Fans of the video game Mirror's Edge might recognise this location from one of the levels featured in the game. It was also used as part of the underground setting as the main characters approach the capital city in The Hunger Games Mockingjay Part 2. So guys, we just returned from the underground tour of the Jikan's drainage tunnel. It was a very surreal experience, I thought. Yeah, it was really magnificent. Now I understand why it's called the underground temple. Definitely. You know, it reminded me of that scene in Lord of the Rings when they're running through the mines of Moria and all the orcs are coming down the pillars. Yeah, especially with the mist, you know, that adds on to the mystical atmosphere. Oh, definitely, yeah. You know, the mist is created by the difference in temperature. So outdoors today it's 32 degrees, scorching hot, but down in the tunnel it's actually 18 degrees. Right. And it creates all this condensation, very spooky mood, yeah. Since its construction, Tokyo's underground temple has reduced flooding in the capital by around 80%, and is certainly a modern marvel of engineering. If you're interested in taking the tour for yourself, then you can find some helpful links down in the video description. Like this video if you found it interesting, and be sure to subscribe to Rew Tokyo for new videos every single week. You can also stay up to date with all the biggest news by checking out our podcast, This Week in Japan. Thanks for watching, and we'll see you again next time.