In Need of a Hero? Here's Super Levee!

The next installment of the PBS television feature I noted in my last post, here, discussed a number of technologies being incorporated to protect Tokyo and other coastal areas of Japan from water inundation. One intriguing idea being used along the rivers of Tokyo are so-called "Super Levees."  As described in a 2013 publication:

"The plan dictates that the current 10-meter-high embankments will remain, but their slope will change dramatically. The ground is to be raised by up to 15 meters to meet the current levee height before gently sloping downward. This way flood waters will flow gradually onto and away from the levee without breaking it. The super-levee will be an enormous piece of infrastructure fully integrated into a rebuilt community."

An engineer featured in the documentary explained that residents of neighborhoods along the rivers are evacuated (his term) and that their homes are razed, the land built-up behind the super-levee, and then the communities are rebuilt and re-occupied.  It's mitigation on a mind-bending scale, but apparently worth the investment, given the importance of Tokyo as a vibrant center of economic activity for the country and the World as a whole.

Another article on the subject (and the source of the photo above) states that "levee failure is inherent to levee construction:

"Levees constantly, gradually fail: their bulk is subject to decomposition and settling; their tops are eroded and their foundations are undermined and underseeped; their bases subside from lack of sediment, the contained rivers rise against them from too much of it. It would seem that to build a levee is to plant the seeds for its own destruction.

"And yet levees and flood-protection works are inescapable. Many cities, including New Orleans, Amsterdam, and Venice would not exist without them. And as sea-levels rise, cities with infrastructure and populations concentrated at the water's edge will inevitably turn to walls and barriers to keep out the water.

"Although the world most often turns to experts from the Netherlands when planning for this wet future, Japan has been quietly building a robust flood-protection system that might provide equally sophisticated lessons. Most interestingly, Japanese engineers have been experimenting with a fail-proof, low-maintenance levee for the protection of urban areas in flood-prone cities like Tokyo and Osaka."

The article goes on to describe much of what is also covered in the PBS documentary, that these super-levees are large-scale earthworks that are best constructed where land is available or, as noted above, where residents and other occupying functions can be temporarily relocated.  Of particular interest to this blog is the following statement that underscores the final point(s) made in the PBS piece, that, like everything else in Japanese society it seems, Japan has learned to live with their environment, rather than trying to control it.

Japan has learned to live with their environment, rather than trying to control it.

The article concludes:  The lesson from Japan is to consider flood-protection not as the isolated endeavor of a single agency, but as part of a larger body of work that is intertwined with urban re-development, open-space planning, land rehabilitation, and habitat generation. Most importantly, the Japanese model proves that protecting our cities from floods does not mean shutting them off from the water. With many of the levees around the country protecting our crops rather than our lives, sophisticated levee solutions will also have a rural application. Although no one in the U.S. has yet embraced Japan's example, the inadequacy of our current flood protection models is being increasingly exposed.