How Japan Keeps Millions of Residents Safe From Floods

The video discusses the world's largest underground water facility located near Tokyo. This facility, known as the metropolitan area Outer Underground Discharge channel, is a massive tunnel system built to prevent flooding in the region. It features a network of vertical shafts that store floodwaters and redirect them to a river capable of handling the excess water. This system protects over 9 million residents from flooding.

How deep is the tunnel that sits underground?

What happens to the floodwaters instead of inundating nearby towns?