Tokyo’s flood control system:
Tokyo is an impressive city above ground, but it is maybe an even more impressive city under ground with it's mind-bogglingly flood control system. This flood conrol system is called the G-Cans Project and begun 12 years ago, to build infrastructure for preventing overflow of the major rivers and waterways spidering the city (A serious problem for Tokyo during rainy-season and typhoon season). The underground waterway is the largest in the world and sports five 32m diameter and 65m deep concrete containment silos which are connected by 6.4 kilometers of tunnel sitting 50 meters beneath the surface:
The project is located in the northern suburbs of Tokyo in Saitama prefecture. The red line in the picture below shows the course of the flood control system:
The projects control building is located here, and here you can see one of the drains that collects the flood water in the tunnels in case of a flood. The five concrete containment silos are located here (the most eastern one), here , here, here , and here (the most western one).