How Japan Keeps Millions of Residents Safe From Floods

- [Narrator] Should a flood hit, Japan is ready. And their solution is the largest underground water facility in the world. (mellow electronic dance music) About an hour outside of Tokyo is the Metropolitan Area Outer Underground Discharge Channel. This tunnel sits 160 feet underground, and is around 4 miles in length. Inside is a network of large vertical shafts that store flood waters. The giant tunnels were built because this area of Japan was constantly flooding. Now, instead of inundating nearby towns, the water flows underground and is diverted to a river that can handle the influx of water, making sure more than nine million residents stay dry. (mellow electronic dance music) (ding)