The Metropolitan Area Outer Underground Discharge Channel

One of the world's largest underground discharge channels was built to protect low-lying areas in eastern Saitama Prefecture from flood damage, which heavy rains have repeatedly flooded. A large-scale flood control system takes swollen water from small and medium-sized rivers such as the Nakagawa, Kuramatsu, and Oootoshi-furut one Rivers underground. Then, it discharges it into the Edo River through a 6.3 km-long tunnel.

The rising river water is fed into the pressure control tank through an overflow dike on the river bank, a shaft like a massive cylinder (connecting the ground and underground), and a tunnel 50 meters underground. Then, finally, it is discharged into the Edo River using a vast pump at the back of the tank. The pressure control tank is 177 m long, 78 m wide, and 18 m high, with 59 pillars supporting the ceiling. It is also known as the "Underground Temple of Disaster Prevention" because it resembles a giant temple.

The facility is usually in operation only a few times a year, and tours are offered on days when the facility is not in process. There are three types of tours: the Impeller Exploration Course (110 minutes), the Shaft Experience Course (110 minutes), and the Underground Temple Course (60 minutes), all of which include a lecture on the Metropolitan Area Outer Discharge Channel system and a visit to the pressure control tank (underground temple). The flow of each course is introduced in detail on the official website, so you can choose the one that best suits your time and interests. Reservations are also made in advance through the official website.