Just after 5 a.m. on August 30, water began flooding a vast underground chamber called the "cathedral" in Saitama Prefecture. The gushing water, captured by security cameras, was the rain that was drenching the capital region as Typhoon Shanshan lashed southwest Japan, 600 km away.
The cathedral and its vast network of tunnels did their job: they prevented a vulnerable river basin in the metropolis from flooding. But as global warming causes more severe weather, authorities are having to give the system a major upgrade.
"As the temperature rises, the amount of water vapor in the atmosphere increases, resulting in relatively larger quantities of rainfall," said University of Tokyo professor Seita Emori, who is a member of a climate science group that won a Nobel Prize in 2007.
"We anticipate that previously unseen amounts of rain will fall as the temperature rises in the future," he added.
Japan is prone to numerous natural disasters, from earthquakes and volcanic eruptions to typhoons and landslides. And like much of the world, the nation is dealing with unprecedented weather due to global warming.
This summer was the hottest ever since records began in 1898, while record rainfall in northern regions resulted in disastrous flooding in July, according to the weather agency. In Tokyo, sudden, violent storms known as "guerrilla" showers have become increasingly common.
The cathedral complex, officially called the Metropolitan Outer Area Underground Discharge Channel, took 13 years and 230 billion yen to build. Since coming online in 2006, it has already prevented more than 150 billion yen in flood damage, the land ministry estimates.
In addition to its engineering ingenuity, the complex is a popular tourist spot and filming location. The cavernous expanse has the capacity to hold the water in almost 100 Olympic-sized swimming pools.
Inside are 59 massive pillars, each weighing 551 tons and stretching 18 meters tall. When nearby rivers flood, the overflow courses through 6.3 km of massive underground tunnels before collecting in the reservoir.
Descending about six floors to the bottom of the chamber is an otherworldly experience. It has its own microclimate, much cooler than the surface in the summer and warmer in the winter. Clouds of mist obscure the top of the pillars.
The dim interior, punctuated by spears of natural light from apertures in the ceiling, and towering pillars evoke an ancient religious structure, giving rise to names such as "the cathedral", "the shrine" or "the temple".
The drop of the No. 1 shaft is deep and wide enough to comfortably hold the Statue of Liberty.
The system kicked in four times in June, more than all of last year. During Typhoon Shanshan, it captured enough water to fill the Tokyo Dome baseball stadium almost four times, before pumping it safely into the Edogawa River and out to sea.
"Compared to years past, there's a tendency for a great deal of rain to come down all at once in what we call guerrilla downpours," said Yoshio Miyazaki, the land ministry official in charge of the complex.
"If this facility didn't exist, the water levels of the main Nakagawa River and its tributaries could rise much higher, leading to flooding of homes and even deaths," he said.
Even so, the system couldn't stop the inundation of more than 4,000 homes in the river basin from heavy typhoon rains in June 2023. Those floods prompted authorities to embark on a seven-year, 37.3 billion yen project to bolster levees and water drainage in the area.
And closer to the centre of Tokyo, another major project is underway to link channels that take in overflow from the Shirako and Kanda rivers. When completed in 2027, it will carry floodwater about 13 kms underground out to Tokyo Bay.
Tokyo's sewer network is designed to handle rainfall of up to 75 mm per hour, but increasingly there are localized storms bringing down as much as 100 mm, overtaxing the system, said Shun Otomo, a construction site manager for the project.
"For example, if there is a temporary downpour in the Kanda River basin, we can tap the watershed capacity in basin areas where it isn't raining," Otomo said. "We believe that will be effective against these guerrilla rains."
© Thomson Reuters 2024.
20 Comments
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Mike_Oxlong
It's good of them to prepare for the unpredictable. Some years get more rain than others. Floods can happen. This was true fifty, one hundred and a thousand years ago. Still true today. Cool that technology can solve age-old problems.
wallace
An amazing feat of engineering.
aaronagstring
“Roaring Fires, Malt Beer, Ripe Meat Off The Bone!”
Looks impressive; that first picture is very ‘Mines of Moria-esque.’
Newgirlintown
Fossil fuels. Best get off them.
tora
Guessing you don't practice what you peach. Would involve turning your phone/computer off for a start.
Raw Beer
"climate change" rains, really?
Mr Kipling
Was lucky enough to go on the tour when it was finished. One of the best experiences in Japan.
NB
Amazing, but senseless.
Right.
The logical conclusion: Curb the temperatue rise.
Jonathan Prin
So the question is to what level of pouring rain will it be upgraded to.
Because one day, you'll have that level surpassed...
All depends what year back to you decide.
In construction, we usually take into account the last hundred years. Because that data is sure and everyone can be accountable for.
What is before is just based on different pieces of evidence and would require hundreds of more billion yens of works.
fallaffel
What else would you call the tropical-like sudden downpours that are happening more and more in the summer season? It's what happens when the ocean gets warmer.
3RENSHO
The cathedral complex..."
"Much better than pouring concrete into the sea (Tetrapod) I suppose...
Christopher Hood
By chance, the other day I wrote a blog post about the 'cathedral' in relation a visit in August. Here's a link for those who may be interested: https://hoodcp.wordpress.com/2024/09/30/remembering-and-preventing-and-disasters/
Desert Tortoise
climate change" rains, really?
Yes. it works two ways. Warmer oceans strengthen over water storms. The strength of a typhoon is determined by sea surface temperature and absence of vertical wind sheer. Warmer oceans equals more intense typhoon.
A warmer atmosphere can hold more moisture. Antarctica is cold and very dry, essentially a desert in terms of annual precipitation, but because it's cold what snow that does fall tends not to melt or sublime, though is is rapidly changing. But a warm atmosphere can hold more water leading to wetter and more intense storms.
Desert Tortoise
Why is this senseless? It seems to me to be an eminently sensible thing to do. Go back a few years and recall what so-called "Superstorm Sandy" did to New York City, flooding subways and tunnels under the Hudson River. New York could have used a similar system to save it from the flooding it experienced.
albaleo
I feel quite envious. It looks like something from a science fiction movie.
Makoto Shimizu
They should make a feasibility study if it is possible to use all this stored water to use in a air conditioning system, and/or if it is feasible to generate some electricity. Investing so big amount of money just to collect and through away water does not seem to be the best use of resources, some imagination could be applied to extract some benefits other than avoiding floods.
RichardPearce
So, the system was designed to handle the worst case scenario people saw in 1993.
But it's 2024, once in a thousand years weather keeps happening, so the plan is to expand it.
But imagine if, in 1993, the US (just the US mind you) had reduced per capital fossil fuel usage to the level of France.
That would mean the world would already be on the path to meet the 1.5 degree cap on global warming.
TaiwanIsNotChina
Imagine if China never went down the path of using dirty coal to be the world's manufacturer.
socrateos
I found a few related videos.
https://www.youtube.com/watch?v=Rp2l6nFIsZA
https://www.youtube.com/watch?v=nKHTPG-iync
https://www.youtube.com/watch?v=mLCkbjbtKWU
Deluded Brian
I would definitely visit this.