When it rains, it floods: Part 1

I had other plans for this first post.

Then the parts of Texas that we hail from flooded on a pretty grand scale.

I have a mental Rolodex full of snapshots, oddities, and observations. None of them are as crucial as what’s been happening at home. I am astonished by the magnitude of destruction, and my heart swoons when I see the support in the communities we left behind. But neither of those things is surprising: Texas floods, and people band together to help those who most need it, even if they’re in need, too.

It’s hard not to feel at once major empathy and detachment. You don’t know you can feel so much about a landscape you know well until tragedy comes to it, but seeing its destruction only via social media and TV doesn’t present the same human scale. We rely on memories, mental maps, and updates from friends. Yet images are powerful, and this recent round of floods may be the first natural disaster in the U.S. to have been well documented by flying drones. The drone footage provides coverage that was once the domain of local news choppers, another feather in the ever-changing cap of citizen journalism.

I subscribe to the notion that natural disasters like this, while terrible, have the degree of destruction they do because of human activity. If no one built in the Blanco River’s 100-year floodplain in Wimberley, for example, then we would be mourning only the loss of the great centuries-old Cypress tries that were literally torn from the ground. But that is not how we’ve decided to live, and collectively we learn with each disaster how to protect our lives and our properties.

Of course, Texas is not the only place to experience flooding. Flooding is a weather phenomenon that affects every continent, and cultures and communities all over have adopted different approaches for flood control and mitigation.

Tokyo is hands-down the most vast concrete jungle I’ve been in. The Tokyo-Yokohama region is the world’s most populous megacity, and as dense as offices and residences are, the Tokyo Metropolitan Government (TMG) has for decades been using the ground below them to provide services. Whereas much of Texas relies mainly on ancient karst aquifers that developed tens of millions of years ago when most of the state was still a sea floor, the Tokyo-area geology is much younger and denser, allowing the Japanese to burrow much deeper beneath their cities than most municipalities in Texas can even afford to dream of.

An example to illustrate the above: the deepest subway platform in Tokyo is the Toei Ōedo Line platform at Roppongi station, at 42 meters/137.8 feet below street level, roughly the same height of a 12-story building. Comparatively, the Edwards Aquifer Authority reports its namesake aquifer goes far deeper, holding freshwater as far down as 3,400 feet; however, 1,250 sq. miles of the aquifer’s karst is exposed at its surface, and the karst is very porous and decays more easily than other types of rock. (I enjoyed reading about the Edwards aquifer’s hydrogeology, so if that’s your thing, read up here.)

The ground beneath Tokyo and its surrounding areas is a great alluvial plain, where sediment from the rivers that now provide drinking water once deposited sediments that sorted themselves into peat, clay, and gravelly soils. This kind of geology has allowed local governments to make and implement some pretty radical flood mitigation systems. This is a good thing, because not only does the area get a lot of rain during tsuyu, the early summer monsoon season, but Pacific typhoons hit the area almost every year.

So how does a megacity protect itself against floods brought on by monsoons and typhoons? A quick Google search found this tidbit of TMG flood mitigation planning on Next City: levees that currently line the Arakawa (the Ara River) will become super levees. The Arakawa forms most of the border between Tokyo and Saitama prefecture, and Clint and I are no stranger to these levees. We’ve had picnics on them, went for jogs along them, and watched fireworks from their riverside slopes. They’re already pretty tall, and it does not seem like hyperbole to me that the author writes these super levees would be akin to “effectively building a small mountain along the Arakawa, running right through the heart of the world’s largest city” …the latter part of which presents a set of social and economic consequences worthy of a dissertation.

A poster illustrates the super levee changes in Edogawa Ward, Tokyo. Credit: Japan Times "Yen For Living" blog
A poster illustrates the super levee changes in Edogawa Ward, Tokyo. Credit: Japan Times “Yen For Living” blog

Perhaps more impressive is the unsexily named Metropolitan Area Outer Underground Discharge Channel. It’s also known as the G-cans Project, so we’ll just go with that. The G-cans Project is an underground network of massive silos connected by equally large tunnels. The website Floodlist lays out the dimensions:

The system consists of 6.4km of tunnels up to 50m (163ft) underground connecting five giant silos 65m (211ft) high and 32m (104ft) wide to one massive tank, the “Underground Temple.” This giant reservoir is the centrepiece of the system, and is a flood chamber or surge tank measuring 125.4m (82ft) high, 177m (580ft) long and 78m (256ft) wide, with the roof supported by 59 pillars.

Just… damn! The G-cans Project was a huge investment, but has been well worth the cost. Since its completion in 2006, the system has been used at least 70 times, diverting flood water from the urban hardtop in the northern reaches of suburban Tokyo into the Edo River.

For what it’s worth, Pharrell really really really digs Tokyo. He digs it so much that he did a series of short videos based there just months after the Great Tohoku Earthquake, during one of which he takes a tour of the G-cans Project. The Project is actually north of the Tokyo city limits in Kasukabe City, which is very near our Japanese hometown of Saitama City. Pharrell’s video provides a human scale and includes a bit of footage of the system in action. Skip ahead to 0:40 to see the segment, if you must. (Bonus: a Japanese dude wearing a shirt that says, “No Nukes! Yes Cannabis!”)

Most recently, though, Tokyo built an underground tunnel to hold excess water during storms and typhoons. When the storm is over, the water is pumped up and into the Furukawa a short distance from Tokyo Bay. According to Bloomberg, Tokyo residents demanded greater flood control measures after a subway station (in an affluent part of town) flooded during a typhoon in 2004. And with climate change churning more frequent and stronger typhoons, hurricanes, and cyclones, Tokyo will surely be using this newer drainage system more often than first anticipated.

On the topic of climate change, I should note that all three of these systems are designed to handle storm water and flash flooding, not flooding that will result from a rising sea level caused by melting polar ice caps. That level of planning deserves its own post, but that post will not be Part 2.

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3 Comments

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  1. Great job Kelly, nice to see you writing!

    Like

  2. Marian (Gomer) June 6, 2015 — 4:37 pm

    I really enjoyed this, Kelly. I look forward to more.

    Like

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