Photo/Illutration The Chikumagawa river overflows its banks in Nagano on Oct. 13, 2019. (Asahi Shimbun file photo)

Dozens of riverbanks that met the central government's standard for strength failed and flooded in recent typhoons, according to the land ministry, a clear sign of the limitation of the nation's flood control policy.

A total of 147 banks at 75 rivers in eastern Japan and the Kyushu region collapsed during Typhoon No. 19 in 2019 and the subsequent rains and the torrential rains in July this year.

Among these, 84 riverbanks, or almost 60 percent, were deemed to have adequate strength as their construction was completed according to the government's strength standards.

These locations include the upper stream of the Abukumagawa river in Fukushima Prefecture, the Yoshidagawa river in Miyagi Prefecture and the Kumagawa river in Kumamoto Prefecture.

In Nagano Prefecture, a bank at the Chikumagawa river failed over a stretch of approximately 70 meters during Typhoon No. 19.

Construction of the riverbank was completed in 1984, and an embankment was also established there.

The banks--designed to be strong enough to hold back raging waters--were built by the central and prefectural government entities that manage Japan's rivers in preparation for catastrophic flooding thought to strike only once in a century or two.

But in recent years, the country has been hit more frequently by record-setting torrential rains due to climate change.

The number of extremely heavy rains packing more than 50 millimeters of rainfall in an hour have increased 1.4 times more in the past three decades or so, exceeding the capacity of existing riverbanks, according to the ministry.

Many officials presume the trend will continue.

“Only strengthening a riverbank isn't going to do anything for flood control today,” a prefectural official said.

After rivers in western Japan flooded and much of the region was damaged by heavy rains in July 2018, among other disasters, the ministry applied an emergency measure to strengthen riverbanks and conducted a survey of about 21,000 rivers nationwide.

But the 147 riverbanks that failed during Typhoon No. 19 and the rains in July this year were exempt from the survey because they were considered “less urgent.”

“We can’t make a pinpoint prediction about where exactly a riverbank might collapse in a disaster,” the prefectural official said. “We need to work as a region and together with local residents and businesses to reduce potential damage.”

Oct. 12 marked the one-year anniversary of Typhoon No. 19, which caused major flooding when it struck eastern Japan and other areas.

As of Oct. 1, a total 7,895 people, or 3,485 households, were still living in temporary housing in 10 prefectures and Tokyo after evacuating due to the disaster, according to the Cabinet Office.

At least 105 people have died from the disaster in Tokyo and 12 prefectures including Fukushima, Miyagi, Nagano and Kanagawa, according to authorities.

The death toll includes people who died from causes associated with the disaster.

Three people remain missing.

More than 30,000 homes in 16 prefectures and Tokyo were either partially or severely damaged by the typhoon.

(This article was written by Takaoki Yamamoto and Yosuke Watanabe.)

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