Tokyo to expand underground ‘cathedral’ complex to handle more extreme storms

Oct 3

Craig Nigrelli Anchor

By Craig Nigrelli (Anchor), William Jackson (Producer), Jake Maslo (Video Editor)

Tokyo is upgrading its flood defense systems to counter the increasing threat of extreme storms fueled by climate change. The city’s Metropolitan Outer Area Underground Discharge Channel, a massive network of tunnels and reservoirs, has played a crucial role in preventing major flooding since it became operational in 2006.

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#GravitasTokyoEdition | Do you know Tokyo has an underground tunnel to catch flood water? It was constructed 3 decades back to save the city from drowning. WION's Managing Editor @palkisu visited the facility to see how it works. Here's a ground report. pic.twitter.com/yLUWkjGoP3
— WION (@WIONews) May 25, 2022

In August 2024, Typhoon Shanshan brought torrential rains to Tokyo, even though the storm’s center was nearly 400 miles away.

The storm filled a vast underground chamber known as the “cathedral,” part of the discharge channel.

The system has saved Tokyo from billions of dollars in potential flood damage by diverting water from densely populated areas.

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The cathedral chamber, located six stories underground, contains 59 pillars that each weigh more than 1.1 million pounds and stand nearly 60 feet tall.

These pillars support a reservoir capable of holding water equivalent to nearly 100 Olympic-sized swimming pools. The chamber’s drop shaft is large enough to fit the Statue of Liberty inside.

Kasukabe, #Saitama Pref.’s Metropolitan Area Outer Underground Discharge Channel is the world’s largest underground flood water diversion facility! People can explore this marvel, feel its power, and understand #DisasterPrevention. https://t.co/o3tyffdyW5 #RegionalRevitalization pic.twitter.com/OraEr20B92
— japan (@japan) November 12, 2022

Despite the system’s effectiveness, Tokyo’s defenses are under increasing pressure as storms grow more frequent and severe.

Sudden downpours that release large amounts of rain in a short time are testing the city’s infrastructure.

To address this, Tokyo has launched a seven-year, $250 million initiative to expand and upgrade its flood defenses. This includes reinforcing levees, improving drainage, and building new reservoirs to increase capacity.

Tokyo’s current sewer system is designed to handle up to 3 inches of rain per hour, but recent storms have brought as much as 4 inches, pushing the system beyond its limits.

New projects aim to raise this threshold to better manage extreme weather events.

The Metropolitan Outer Area Underground Discharge Channel, which cost $1.63 billion to build over 13 years, has become a global model for urban flood control.

Officials say further upgrades to the system will be completed by 2027 to ensure it can meet the growing challenges posed by climate change.

Tags: Extreme weather, flooding, Japan, Tokyo

[Craig Nigrelli]

TOKYO HAS LONG FOUGHT THE BATTLE AGAINST INTENSE RAINFALL, BUT WITH CLIMATE CHANGE FUELING MORE EXTREME STORMS, THE CITY IS RACING TO UPGRADE ITS FLOOD DEFENSES.

IN AUGUST 2024, TYPHOON SHANSHAN BROUGHT TORRENTIAL RAIN TO TOKYO, EVEN THOUGH THE STORM’S CENTER WAS NEARLY 400 MILES AWAY. THE STORM FILLED A VAST UNDERGROUND RESERVOIR KNOWN AS THE “CATHEDRAL,” PART OF TOKYO’S MASSIVE FLOOD CONTROL SYSTEM THAT HAS BEEN A CRITICAL LINE OF DEFENSE SINCE 2006.

THIS NETWORK OF TUNNELS AND RESERVOIRS SPANS OVER FOUR MILES AND HAS SAVED TOKYO FROM BILLIONS OF DOLLARS IN POTENTIAL FLOOD DAMAGE BY DIVERTING WATER AWAY FROM DENSELY POPULATED AREAS. THE “CATHEDRAL” CHAMBER, LOCATED SIX STORIES UNDERGROUND, CONTAINS 59 MASSIVE PILLARS THAT EACH WEIGH MORE THAN 1.1 MILLION POUNDS AND STAND NEARLY 60 FEET TALL.

THE RESERVOIR IS CAPABLE OF HOLDING NEARLY 100 OLYMPIC-SIZED SWIMMING POOLS WORTH OF WATER. THE CHAMBER’S DROP SHAFT IS LARGE ENOUGH TO FIT THE STATUE OF LIBERTY INSIDE.

DESPITE THE SYSTEM’S CAPABILITIES, OFFICIALS SAY TOKYO’S DEFENSES ARE BEING STRAINED AS STORMS GROW MORE FREQUENT AND SEVERE. EXTREME WEATHER EVENTS, INCLUDING SUDDEN DOWNPOURS THAT RELEASE LARGE AMOUNTS OF RAIN IN A SHORT TIME, ARE TESTING THE CITY’S INFRASTRUCTURE. IN RESPONSE, TOKYO IS LAUNCHING A SEVEN-YEAR, $250 MILLION INITIATIVE TO EXPAND AND UPGRADE ITS FLOOD DEFENSE SYSTEMS. THIS INCLUDES REINFORCING LEVEES, IMPROVING DRAINAGE SYSTEMS, AND CONSTRUCTING NEW RESERVOIRS TO INCREASE WATER STORAGE CAPACITY.

TOKYO’S CURRENT SEWER NETWORK IS DESIGNED TO HANDLE UP TO 3 INCHES OF RAIN PER HOUR, BUT RECENT STORMS HAVE BROUGHT AS MUCH AS 4 INCHES PER HOUR, PUSHING THE SYSTEM BEYOND ITS LIMITS. NEW PROJECTS AIM TO RAISE THIS THRESHOLD TO BETTER MANAGE THESE EXTREME WEATHER EVENTS.

TOKYO’S UNDERGROUND DISCHARGE CHANNEL, BUILT AT A COST OF $1.63 BILLION, HAS BECOME A GLOBAL MODEL FOR URBAN FLOOD CONTROL. SINCE ITS COMPLETION, THE SYSTEM HAS BEEN ACTIVATED MORE FREQUENTLY AS HEAVY RAINS BECOME MORE COMMON. DURING TYPHOON SHANSHAN, THE SYSTEM CAPTURED ENOUGH WATER TO FILL TOKYO’S DOME BASEBALL STADIUM FOUR TIMES OVER, PREVENTING MAJOR FLOODING IN THE CITY.

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