Driftwood key factor in flood damage

The Yomiuri Shimbun

Rescuers search for missing people in the Hakihoshimaru district of Asakura, Fukuoka Prefecture, on Sunday morning.

The Yomiuri Shimbun FUKUOKA — Record rainfall in northern Kyushu triggered severe damage, especially in Asakura, Fukuoka Prefecture, by causing an agricultural reservoir to burst and freeing a large amount of driftwood that subsequently blocked a river, according to on-site research conducted by an expert.

Kyushu University Prof. Shinichiro Yano, an expert on rivers, on Saturday visited the city’s Yamada district, where at least two people were found dead, and other areas. Yano confirmed that the agricultural reservoir, which has a storage capacity of up to about 67,000 cubic meters, had been breached upstream from the district.

A great deal of driftwood and a large amount of water may have accumulated in the reservoir because of the heavy rains, as runoff from the river pours into the container.

“I believe the accumulated driftwood and water poured into the downstream area at the same time, once the reservoir burst,” Yano said.

In the Yamada district, a tree longer than a human body was found, as well as a tree with a circumference of 1.6 meters.

In the city’s Hakishiwa district, located about two kilometers from the broken reservoir, Yano also found a great deal of driftwood that had been pinned near a bridge connecting a stream originating from the Chikugogawa river.

According to Yano, the bridge and the driftwood appear to have blocked the river, forming a kind of dam. A large volume of water flowed into neighboring areas because it had nowhere else to go.

Yano said the smaller a river is, the easier it is for flooding or similar disasters to happen because driftwood blocks the flow.Speech

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