Tokyo's 'Underground Cathedral' Stores and Redirects Excess Flood Waters

Tokyo's 'Underground Cathedral' Stores and Redirects Excess Flood Waters

Editor’s note: This post was originally published on the SWA Group/IDEAS blog and re-published here with permission.


 image ©  Wiki Commons

image © Wiki Commons

While back in Japan last month, I learned of Houston’s Hurricane Harvey. The breath-taking videos of large-scale flooding were widely broadcasted on the morning and evening news programs there. The images of drowning buildings, highways, and trees under the extensive muddy water were a shocking reminder to the Japanese of their own 2011 Tsunami, in northern Japan.

Tokyo, the nation’s capital, rests on the country largest plain—with a geographical scale about a half of Houston’s area—and is also close to sea level, with five major rivers flowing through. Because of its setting, seasonal storms and pacific typhoons kept putting the cities under water historically. Flood control has been one of the key agenda items for the regional lords and the nation’s governors to tackle over the past 500 years. They tried to manage the rivers with the available technologies in each age. Building levies, dredging channels, and rerouting rivers all worked somehow to disperse the water flows and energy, however, those classical measures never caught up with the rapid, extended, and intensified urbanization of the region and the cities were occasionally submerged.

There is a popular new tourist attraction located on the outskirts of the metropolitan area, with access totally controlled and only a limited number of people allowed each day. Although there is no icon, no seating, and no pipe organ, people call it ‘The Underground Cathedral’. Every visitor who has taken the 116 steps down into the space has been impressed and somewhat overwhelmed by its scale and structure, and especially by its hidden power to ease the challenges of nature.

The formally named Metropolitan Outer Floodway, a series of huge concrete structures built under a major highway, totals six cylinders and subsidiary pressure control cisterns connected by a four-mile-long tunnel, with each unit measuring 230 feet deep and 100 feet in diameter. They store up to 900,000 cubic yards of runoff water during heavy storm events and discharge it in a controlled manner. The complex took 20 years and cost $2 billion to construct and it is estimated that the facility has averted $15 billion of potential economic damage in Tokyo since it began operation 15 years ago.

We will keep experiencing ‘record-breaking’ or ‘unpredicted’ natural disasters related to climate change. Estimates of the economic damage that Harvey and Irma caused have reached $200 billion. It may be worth spending comparatively less money in advance to build mega-scale infrastructures such as those outside Tokyo in order to save a trillion dollars and to protect people’s lives in the future. What’s the alternative? Some of the towns devastated by the Tsunami already moved their settlements to higher grounds; they do not want their children to experience the catastrophic tragedy they endured.

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