At the mouth of the river that flows into Osaka Bay, there are three unusually shaped locks.



An “arch-shaped floodgate” that is rare in Japan.

All three have been in operation for over 50 years.



It greatly contributed to prevent flood damage from spreading to Osaka city even during the typhoon four years ago.



However, in preparation for the huge Nankai Trough earthquake, construction work to rebuild the new floodgate will begin this year.



However, it will be about 20 years after all three units are renewed.



The "arched floodgate" is still active and will continue to play a role in protecting the city of Osaka from flood damage.

Defeat the arch in the river to prevent water

As the name suggests, an "arched lock" is a lock that looks like a large bridge, and it takes about 30 minutes to knock down the arched part on the upstream side of the river.

By doing so, the waterway is blocked by a lock that is about 12 meters high and protects the city from the storm surge that rushes from the estuary.

All three units around Osaka Bay have been in operation for over 50 years.

There are three such "arch-shaped floodgates" in Osaka City (Yasujigawa floodgate, Shirinashigawa floodgate, and Kizugawa floodgate).



Many people think of "water gates" as descending vertically, but



why are there "arch-shaped" water gates around Osaka Bay?

As Osaka was once called the "kitchen of the world," commerce was flourishing, and various things from all over the country were brought to the center of the city through the river.



It was arched so as not to block the traffic of such ships.



Factory work boats and tour boats are still sailing under the floodgates.

Protected the city of Osaka from flood damage

This "arched floodgate" demonstrated its power in September 2018.



Typhoon No. 21 struck the archipelago, causing great damage such as the flooding of Kansai Airport in Osaka.

This is the state of the Kizugawa floodgate when Typhoon No. 21 approaches.



The floodgate prevents the storm surge from Osaka Bay (on the right side of the screen).



These locks, as a fort against the storm surge, greatly contributed to the prevention of flood damage in Osaka City.

"Arch-shaped floodgate" over 50 years old needs to be rebuilt

The three locks were completed in 1970 (Showa 45), about 50 years ago, and are aging.



In addition, when a huge Nankai Trough earthquake occurs in the future, an expected large tsunami rushes in, and the "arch-shaped floodgate" catches the wave, the arch part may be distorted or distorted.



In that case, it may be difficult to open the lock again from the closed lock.



In addition, if the power to operate the floodgate is lost, it may interfere with the closing of the lock.

Rebuilt to a new "gate type"

Therefore, it will take about 20 years from this year to build a new "gate type" floodgate that closes the channel by dropping the floodgate vertically.



The new lock is designed to withstand the tsunami that would be expected from a huge Nankai Trough earthquake.



Furthermore, even if the power supply is lost, the weight of the floodgate itself can block the channel.

It will be demolished after the construction of a new lock

It has been decided that the "arch-shaped floodgate" will be demolished in sequence after fulfilling its role until a new floodgate is completed.



An "arch-shaped floodgate" that has greatly contributed to water control measures in Osaka.


We are still active and will continue to take on the role of protecting our lives and livelihoods.

(Osaka Broadcasting Station Cameraman Kentaro Kurita)