Tokyo upgrades underground super flood tunnel

Shortly after 5 a.m. on August 30, water began pouring into the giant underground storage facility nicknamed “The Cathedral” in northern Tokyo. The massive flow of water recorded by security cameras is rainwater pouring down on the capital Tokyo when Typhoon Shanshan made landfall in southwestern Japan 600 km away, according to Reuters. The “great cathedral” and its extensive network of tunnels have completed the task of protecting the river basin in the megalopolis from flooding. But as global warming makes the weather more severe, authorities need to upgrade the system.

“As temperatures increase, the amount of water vapor in the atmosphere increases, leading to greater precipitation,” said Professor Seita Emori at the University of Tokyo, a member of the climate science team that won the Nobel Prize in 2007. “We predict unprecedented amounts of rain will fall as temperatures continue to rise in the future.”

Japan often encounters many natural disasters, from earthquakes, volcanic eruptions, rainstorms to landslides. This country is facing unprecedented extreme weather due to global warming. This summer has been the hottest since 1898, while record rainfall in the north caused a flooding disaster in July. In Tokyo, fierce and unexpected storms called “guerrilla” are becoming more frequent. increasingly popular.

The “Cathedral” complex, officially known as the Underground Water Discharge Canal on the Periphery of the Megalopolis, took 13 years and 1.63 billion USD to build. Since its launch in 2006, the system has prevented more than $1.06 billion in damage caused by flooding. The cave-like complex is capable of holding the amount of water equivalent to nearly 100 Olympic swimming pools. Inside the complex are 59 giant pillars, each weighing 551 tons and 18 m high. When nearby rivers overflow, floodwater will pass through 6.3 km of underground tunnels before gathering in the reservoir.

Going through 6 floors to the bottom of the bunker is a special experience. The system has a microclimate, much cooler than the ground in summer and warmer in winter. Clouds of mist obscured the top of the column. The dark space is illuminated by natural light coming through the gap in the basement ceiling. The towering pillars are reminiscent of ancient structures, leading to the nickname “Cathedral”. Vault No. 1 is so deep and wide that it can fit the Statue of Liberty.

The system was activated four times in June, more than the total number of operations last year. During Typhoon Shanshan, the structure collected enough water to fill nearly four Tokyo Dome stadiums before emptying safely into the Edogawa River and into the ocean. “Compared to previous years, heavy rainfall tends to fall at the same time,” said Yoshio Miyazaki, an official at the Ministry of Land in charge of the tunnel complex. “If this system did not exist, the water level of the main Nakagawa River and its tributaries would be much higher, leading to flooding of houses and even loss of life.”

Even so, the system cannot prevent flooding of more than 4,000 houses in the river basin after a heavy storm in June 2023. That flood prompted authorities to carry out a seven-year project worth $250 million to strengthen dams and drainage in the area. Closer to central Tokyo, another major project is underway to connect overflow canals from the Shirako and Kanda rivers. When completed in 2027, the system will channel floodwater 13 km underground to Tokyo Bay.

Tokyo’s sewer network is designed to handle up to 75 millimeters of rain per hour, but an increasing number of localized storms can bring up to 100 millimeters of rainwater, overloading the system, according to Shun Otomo, manager construction site in Tokyo. “For example, if there is a torrential rain falling on the Kanda River basin, we can take advantage of the water infiltration in the area that does not rain,” he said.