Water Discharge Tunnel on the Outskirts of the Metropolitan Area

The world's largest underground tunnel, the product of cumulated civil engineering expertise

Did you know that there is a huge underground shrine in the city of Kasukabe in Saitama Prefecture, about 30 km north of Tokyo? It is the Ministry of Land, Infrastructure, Transport and Tourism's "Water Discharge Tunnel on the Outskirts of the Metropolitan Area," which runs over a length of 6.3 kilometers some 50 meters underground. Built over 13 years and completed in 2006, it incorporates the latest advances in Japanese civil engineering.

The city of Kasukabe and surrounding towns are located in the Nakagawa-Ayase river basin, a low-lying area surrounded by large rivers including the Arakawa River, Tone River, and Edogawa River, a location where rainwater easily accumulates as if at the bottom of a dish. Furthermore, since the gradient of the Nakagawa-Ayase River is gentle, restraining the water flow, during heavy rain the water level does not decrease rapidly and flood damage was a frequent occurrence. As a solution, a huge drainage path was built in the form of an underground tunnel to capture the water of each river about to overflow due to heavy rain, and redirect all this water to the Edogawa River.

The two facilities that can be toured are the pressure regulating water tank and the operation room. This place, which could be described as an underground temple, has the role of weakening and smoothing the momentum of water flowing from the underground tunnel in this pressure regulating water tank. The water tank measures 177 m in length, 78 m in width, and 18 m in height. Fifty-nine towering columns that each weighs as much as 500 tons support the ceiling of the tank. The "Water Discharge Tunnel on the Outskirts of the Metropolitan Area" is literally an underground giant that protects the safe living environment of the metropolitan area. Please come and visit this facility to get the overall picture of the technology deployed in the construction and management system, drainage system, and so on, and experience first-hand the overwhelming scale of the place.
Photo by Edogawa River Office, Ministry of Land, Infrastructure, Transport and Tourism


720 Kamikanasaki, Kasukabe-shi, Saitama Prefecture 344-0111
Tour times:
10:00-11:00, 11:00-12:00 (summer vacation period only), 13:00-14:00, 15:00-16:00 * Tours held occasionally on Saturdays, see details on website
Saturdays, Sundays, Holidays, New Year's holiday

Information accurate as of January 13, 2017.

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