"Underground temple" protects the city area drastically reduces inundation damage Saitama Kasukabe October 18, 16:22

In the heavy rain of Typhoon No. 19, the world's largest underground drainage channel, also known as the “underground shrine” in Kasukabe City, Saitama Prefecture, played a role in significantly reducing damage from inundation.

The “Tokyo Metropolitan Outer Floodway” in Kasukabe City was constructed by the country over approximately 230 billion yen to combat flood damage in the eastern part of Saitama Prefecture.

In order to prevent flooding, water taken from the five rivers that flow nearby is discharged into the Edo River, which is wide, using a pump.

It is the world's largest underground spillway with a length of 6.3 km, and a huge tank that accumulates water has 59 pillars and is also called the “underground temple”.

According to the Edogawa River Office, water began to enter the underground aquarium at 11:30 am on the 12th of this month, and started to discharge from the huge aquarium into the Edogawa before 7:00 pm.

The amount of water temporarily stored was about 12 million cubic meters, reaching 9 cups of Tokyo Dome, and the third largest since 2006 when the facility was completed.

According to the river office, compared to Typhoon No. 18 in 1982, which observed the same amount of rainfall as this time, four facilities including this water discharge channel were operated. The inundation damage of the local government has been reduced to less than 1/20 of the previous one.

Masaki Takahashi, head of the Tokyo Metropolitan Outer Discharge Channel Management Branch, said, “If the water level in the Edogawa was one meter higher, we could not drain, but we were relieved to be able to reduce inundation damage in the area.” It was.

Expert “Effective for measures against domestic water”

Prof. Norio Tanaka of Saitama University, who is familiar with river flooding and disaster prevention, said, “When the rivers break down and people think they are dangerous, they may not be able to evacuate due to the flooding of“ inland water ”in the city. It was effective to escape "Uchimizu".

Prof. Tanaka analyzed that the multiple drainage channels and recreational ponds, including the Tokyo Metropolitan Outer Floodway, were effective in reducing inundation damage in the eastern part of Saitama Prefecture, Tokyo Edogawa Ward and Katsushika Ward.

On top of that, it is necessary to check the local hazard map and take appropriate actions such as evacuation without being relieved that there will be a flood even if there is a facility such as the Tokyo Metropolitan Outer Floodway.

In addition to large-scale facilities, measures such as the use of buildings and road basements as recreational ponds need to be strengthened.