*This article is based on content originally published in the July 11 issue of the email newsletter “Takaaki Mitsuhashi’s ‘New’ Keisei Kaimin Shimbun,” and has been edited with the author’s permission and additional contributions.
The Kuma River Breach That Caused Extensive Damage
The “July 2020 Heavy Rains,” caused by the stalled rainy season front over the Japanese archipelago, have caused various types of damage across the country. Among the areas affected, Kumamoto suffered particularly severe damage.This ArticleAccording to reports, the death toll in Kumamoto Prefecture stands at 55, with 9 people still missing (Editor’s note: as of July 9). The reason the damage in Kumamoto has been so extensive is that the Kuma River experienced numerous floods and two breaches in its banks.
The Kuma River receives a large volume of water from numerous tributaries, yet its riverbed is narrow, and it is ranked as one of “Japan’s Three Great Rapids.” With such a fast current, it is only natural that during heavy rains, it becomes a “wild river” prone to flooding. Consequently, all the river engineers were, unfortunately, well aware of the fact that the risk of a major flood like the one that occurred this time was extremely high.
That is why engineers have held numerous discussions regarding “flood control measures” for the Kuma River and have continued to urge the government to implement prompt countermeasures. Throughout this process, the “construction of the Kawabe River Dam” has been the one measure that engineers have consistently advocated as virtually the only realistic solution.
To prevent the Kuma River from bursting its banks, the Kawabe River Dam Project has been underway for 40 years.
According to preliminary technical assessments, it was already known that the “Hitoyoshi” area—where the breach occurred this time—was the most vulnerable point along the Kuma River; calculations had shown that, to prevent flooding there, the river’s flow would have to be reduced by at least “three-sevenths,” or 43 percent.
The most effective and practical solution to this problem was the construction of the “Kawabe River Dam.” Other measures considered included “building a diversion channel” (that is, digging another river to distribute the water) and “constructing a flood detention basin” (building a large pond instead of a dam). However, it was determined that these alternatives would entail additional construction time and costs, leading to the conclusion that building the dam was the most practical solution.
As a result of these developments, the Kawabe River Dam project began in 1966 and, as of 2008, was approximately 70 percent complete.
Under pressure from public opinion advocating that "dams are unnecessary," the dam project was canceled, and no follow-up measures were taken.
However, around the turn of the 21st century, public opposition to public works projects—particularly dams—began to sweep across Japan (despite the sense of urgency regarding local flood risks).
Ikuo Kabashima, the current governor of Kumamoto Prefecture—who was elected amid that atmosphere—went on to declare his opposition to the dam, citing the protection of the natural environment and other reasons. Furthermore, under the Democratic Party of Japan administration, which championed the slogan “From Concrete to People,” the construction project was halted in 2008, along with the Yamba Dam project.
In other words, the Kawabe River Dam project—which had been underway since 1966 and was about 70 percent complete after more than 40 years, aimed at protecting the lives and property of people living along the Kuma River, primarily in Hitoyoshi City—was ultimately scrapped due to the prevailing sentiment at the time that “dams are a waste of money.”
At that point, it could already be said—regrettably—that a major flood like the one we are experiencing now, caused by the breach of the Kuma River, was all but inevitable. After all, if the Kawabe River Dam project had not been canceled in 2008, it would have been completed by 2017 (with a budget of 110 billion yen).
On the other hand, it is estimated that the floodway would require a budget of 820 billion yen and take as long as 45 years to complete. As for the flood detention basin, it is expected to cost 1.2 trillion yen and take more than 100 years to complete. In other words, neither the diversion channel nor the flood detention basin was by any means a “realistic” solution. Consequently, there was no way the government could have approved such projects, and the reality is that construction has not even begun.
In other words, the reality is that in the 12 years since the dam project was canceled, no “fundamental” measures to prevent a breach of the Kuma River have been taken, and we have arrived at this point today. Since, as the engineers had concluded from the outset, there were no realistic solutions other than the dam, we must acknowledge that this outcome was inevitable once the dam project was canceled.
That’s why, even back then, all of us engineers thought, ”Canceling the dam project under these circumstances is tantamount to telling the people living along the Kuma River, ”If heavy rains come, there could be a major flood that might cost lives, but we want you to just accept that as a fact of life!’” And that is exactly what happened in this recent major flood. It is truly heartbreaking.
"Yamba in the East, Kawabe River in the West": The Choice That Determined Their Fates
It was the Democratic Party of Japan, which was in power at the time, that ultimately canceled the construction of the Kawabe River Dam. At that time, the phrase “Yamba in the East, Kawabe River in the West” was frequently cited as a prime example of wasteful spending. Although construction on both projects was halted, the Yamba Dam—fortunately—saw construction resume under the Democratic Party administration and began operations last October.
Furthermore, it played a major role in preventing the unprecedented flooding of the Kanto Plain caused by Typhoon No. 19, which struck just over 10 days later. Therefore, if the Kawabe River Dam had not been suspended at that time, it would likely have played a major role in preventing the recent massive flooding in the Kuma River area.
There is already a dam on the Kuma River called the Ichibusa Dam, but its flood control capacity is only about 10 percent that of the Kawabe River Dam. Therefore, the Kawabe River Dam was indeed indispensable for flood control. Of course, it might have been difficult to prevent all the flooding caused by this torrential rain, which was described as the heaviest on record.
Nevertheless, it is clear that damming such a large volume of water upstream would have significantly reduced the damage. Moreover, the worst-case scenario—the “breaches” that occurred at two locations this time—could very likely have been avoided.
In other words, if only the Kawabe River Dam had been in place, it would undoubtedly have significantly reduced the flooding, prevented the dam from bursting, and avoided such a high death toll.
In other words, within the context of so-called “populist politics,” political decisions made in the wake of the prevailing “public sentiment” of the moment—without due technical consideration—can sometimes lead to consequences that claim the lives of so many people and completely destroy an entire city.
In light of this, I urge officials in Kumamoto Prefecture and the national government to sincerely consider what steps must be taken moving forward—with a firm resolve to ensure that this tragic history is never repeated—and to implement countermeasures as quickly as possible. No matter how much we may regret it after even more lives are lost in the next torrential rain, it will inevitably be too late.
Public works projects, which take many years to complete, are often labeled as “wasteful.” Consequently, there have been numerous tragedies surrounding public works projects, such as the recent “Kawabe River Dam” incident. Japan’s future cannot be realized unless we overcome each of these tragedies one by one.
P.S.: Actually, the first construction project I worked on after starting my career was the road construction around the Kawabe River Dam project.
Since it was my first construction project, I remember it very clearly.
After all, people are creatures who sometimes make mistakes.
I'm hoping things will get back to normal.
