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Reservoirs in deadly Hiroshima landslide didn't receive proper designation

This aerial photo taken on July 14, 2018, shows an area where two reservoirs breached after the ground under a field, top right, gave way in Fukuyama, Hiroshima Prefecture. (Mainichi)

FUKUYAMA, Hiroshima -- In spite of an alert from the national government, the municipal government here failed to designate reservoirs as requiring special disaster prevention measures before they were breached in torrential rain, triggering a deadly landslide, it has emerged.

Akari Kai, 3, died after a landslide hit her house at the foot of a mountain in Fukuyama, Hiroshima Prefecture, on the night of July 7, while her mother in her 30s was rescued. The landslide occurred after the ground under a field just above the two reservoirs on the side of a mountain gave way, resulting in the breach.

The combined capacity of the two reservoirs -- Shobusakokami Pond could hold about 800 cubic meters and Shobusakoshimo Pond about 3,200 cubic meters -- was four times the prefecture's standard for designating ponds as requiring special disaster prevention measures.

In May this year, the Ministry of Internal Affairs and Communications (MIC) pointed out that the city had not properly designated the ponds.

"The ponds in question deserved to be designated as those requiring disaster control measures based on the criteria, but I don't know why they weren't designated as such," a city official told the Mainichi Shimbun.

In around 2000, the municipal government estimated that 12 residents in six households living at the foot of the mountain would be affected if the two reservoirs collapsed at the same time. The field that collapsed -- located around 50 meters away from the ponds and about 15 meters higher in altitude -- had been developed by local communities decades ago.

The city of Fukuyama observed approximately 370 millimeters of rainfall between July 5 and noon on July 7. At around 6:45 p.m. on July 7, the field and nearby slopes gave way, causing the two reservoirs to breach and triggering the deadly landslide, according to local residents.

Municipal governments are tasked with selecting and designating reservoirs as requiring special disaster prevention measures based on the standards set by prefectural governments. The national government has called for hazard maps on such reservoirs to be created to alert local residents to dangers. The Hiroshima Prefectural Government set the designation criteria as "a reservoir with a total capacity of at least 1,000 cubic meters that could cause damage to houses and public facilities." However, the Fukuyama Municipal Government failed to name the two ponds in question as such.

The MIC's Chugoku-Shikoku regional administrative evaluation bureau began a sampling survey on disaster prevention measures for reservoirs in 12 cities in three prefectures including Hiroshima in July last year. In a report released this past May, the ministry pointed out that reservoirs in Fukuyama and other cities had yet to be designated as requiring disaster prevention measures even though their capacities exceed prefectural criteria.

In the torrential rain disaster that hit northern Kyushu in July last year, a reservoir in Asakura, Fukuoka Prefecture, with a capacity below local criteria for such designation breached, causing casualties in lower-lying areas.

An official of a local branch of the Fukuyama Municipal Government overseeing the reservoirs in question said, "We received more rainfall than expected. We hadn't imagined that the ground would give way." The Hiroshima Prefectural Government is planning to conduct an emergency inspection of the ponds.

There are about 200,000 artificial reservoirs created for irrigation across Japan, mainly in areas where major rivers are absent. Such reservoirs are concentrated in areas along the Seto Inland Sea, which have less precipitation, with Hyogo Prefecture topping the list with 43,245 reservoirs, followed by Hiroshima Prefecture with 19,609. Many of them were developed during and before the Edo Period (1603-1868) and their dilapidation has raised the threat they pose in natural disasters.

According to the Ministry of Agriculture, Forestry and Fisheries, about 8,800 artificial ponds suffered damage from natural disasters over a 10-year period up to 2016, of which 70 percent was caused by torrential rains and the remaining 30 percent by earthquakes. In the Great East Japan Earthquake in 2011, many agricultural dams and artificial reservoirs breached, causing casualties.

Between fiscal 2013 and 2015, the agricultural ministry instructed local governments to inspect reservoirs across the country, and about half of them -- or some 96,000 reservoirs -- were covered by such inspections. The ministry's calls for local bodies to select and designate artificial ponds as requiring disaster control measures also resulted in around 11,000 reservoirs being listed as such. A ministry manual for inspections drawn up in 2016 urges that attention be also paid to areas above and around such ponds.

The agricultural ministry has also requested local municipalities to put together hazard maps by fiscal 2020 for possible inundation areas in the event designated reservoirs breach. However, such maps of only about 4,000 locations had been released as of the end of March 2017.

In Hiroshima Prefecture, hazard maps for only 25 out of 503 such reservoirs have been released.

(Japanese original by Kensuke Yaoi and Takuya Horie, Osaka City News Department)

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