30/09 Landslide dangers left unaddressed

The Yomiuri Shimbun

Prefectural surveys have found that precautionary measures need to be taken at about 295,000 locations to deal with landslides, but more than 20 percent have not yet been officially designated as needing such measures, The Yomiuri Shimbun has found.

About 14,000 spots have been left undesignated for more than two years since the surveys were conducted by prefectural governments. The high number is chiefly due to prefectural governments' difficulty in winning the approval of local municipalities and residents for the designation.

In Wakayama Prefecture, recently battered by Typhoon No. 12, about 70 percent of the locations found to need designation have not yet been recognized.

Prefectural governments survey areas deemed in danger of landslides, including their geographical features, based on the law enacted in 2001 concerning prevention of landslides.

If an area is found to need such measures as establishing an evacuation system, the prefectural government will designate the location as needing precautionary measures after hearing the opinions of local municipal leaders.

When an area is designated, the local municipal government has to establish a community wireless system and devise hazard maps showing possible landslide areas, so as to make residents aware of the danger.

The Yomiuri Shimbun learned from interviewing prefectural governments that surveys had been conducted at about 310,000 locations as of the end of August. About 295,000 of these were found to need designation as areas requiring precautionary measures.

Of the 295,000 locations, about 65,000 were still undesignated, with some locations still undesignated even though they were surveyed seven years ago.

Saga Prefecture had the highest percentage of undesignated spots: 2,512 out of 3,065, or 82 percent.

In Wakayama Prefecture, where the recent typhoon left 74 people dead and 21 people missing, 3,024 out of 4,330 locations found to need the designation were yet to be designated. At one such place, a man was killed in a landslide during the recent typhoon.

In Nara Prefecture, 4,144 out of 8,595 locations found to need the designation had yet to be designated.

Regarding reasons for the delay, officials of the Saga, Wakayama and Nara prefectural governments said they had to spend a great deal of time explaining the matter to municipal governments and residents and coordinating opinions with them.

An Oita prefectural official said it had yet to win consent from local residents, as they feared such designations will reduce the value of their land.

According to the Land, Infrastructure, Transport and Tourism Ministry, 227,804 locations had been designated by the ministry as needing precautions against landslides as of the end of August, and 107,963 spots had been designated as needing special precautionary measures.

"As designations are being made mainly by prefectural governments, we can't instruct or force local municipalities to take precautionary measures. Nonetheless, it is not desirable to postpone the designation, as it will hinder the evacuation of residents during disasters," an official of the land ministry said.

The law concerning the prevention of landslides was enacted following the torrential rain that induced landslides in Hiroshima Prefecture in 1999, killing 24 people.

Once designated as needing precautionary measures, a local government has to make its residents aware of the danger and improve its evacuation procedures for residents.

When designated as needing special measures--as a result of being particularly susceptible to landslides and greater damage expected--restrictions are placed on the development of residential land and building structures.

(Sep. 30, 2011)

17/09 Rain could burst dams in Nara, Wakayama prefs

The Yomiuri Shimbun

A landslide dam in the Akatani district of Gojo, Nara Prefecture

With heavy rain predicted from Friday evening near landslide dams in Nara and Wakayama prefectures, the land ministry was calling for some residents to evacuate due to the possibility of further serious landslides and floods in their areas.

The dams were formed by landslides triggered by strong rains dumped by Typhoon No. 12 earlier this month.

According to the Land, Infrastructure, Transport and Tourism Ministry's Kinki Regional Development Bureau, water levels had not yet risen significantly behind two landslide dams deemed at particular risk in the Akatani district of Gojo, Nara Prefecture, and in the Iya district of Tanabe, Wakayama Prefecture.

However, the bureau said 10 to 30 millimeters of rain could lead to the dams breaking.

If the dam in the Akatani district breaks, a flow of mud and rocks about 300 meters wide could travel about 20 kilometers downstream, it said.

As a result, a nonbinding evacuation directive has been issued to 521 people in 270 households in the two prefectures. The ministry began building emergency water conduits in the Akatani and Iya districts on Friday afternoon.

There were also fears of a break in the Obatakedoro landslide dam that was created in the Nagai area of Totsukawamura, Nara Prefecture, as a result of massive rains in August 1889.

Evacuation advisories were issued Friday to 45 people in 21 households living below the dam in the Shigesato area of Totsukawamura. A total of 178 people in 92 households live in Shigesato.

The area saw only minimal landslides as a result of the heavy rain brought by Typhoon No. 12, prefectural authorities said.

According to the Meteorological Agency, Typhoon No. 15 was hovering near Okinawa Prefecture, pushing moist air up from the south toward the Kii Peninsula. This was expected to cause particularly heavy rain from Friday evening through Saturday evening.

Some areas of Nara and Wakayama prefectures may see as much as 300 millimeters of rain in the 24 hours to noon Saturday, the agency said.

(Sep. 17, 2011)

07/09 Typhoon No. 12 caused deep-seated landslides

The Yomiuri Shimbun

This photo taken Monday shows a mud slide in Tanabe, Wakayama Prefecture.

Large mud slides in Wakayama and Nara prefectures resulting from Typhoon No. 12 are suspected of being deep-seated landslides, according to a specialist.

Unlike shallow landslides in which topsoil 0.5 meters to 2 meters deep comes loose, the bedrock beneath the topsoil also moves in deep-seated landslides, causing enormous damage.

Typhoon No. 12 brought record rainfall to the Kii Peninsula, where fragile bedrock allowed massive amounts of rainwater to permeate underground. This has sparked concerns that more deep-seated landslides could occur in the region.

Kyoji Sassa, a professor emeritus of Kyoto University, has warned the peninsula will frequently be hit with similar landslides in the future due to its geological features.

Sassa analyzed news photos following Typhoon No. 12 of a mud slide in the Fudono district of Tanabe, Wakayama Prefecture, and suspects it is a deep-seated landslide. He also believes a mountain collapse in Gojo, Nara Prefecture, could be a deep-seated landslide.

Asahiko Taira, a geologist and executive director of the Japan Agency for Marine-Earth Science and Technology, said the Kii Peninsula is formed with Shimanto-tai strata, which are highly prone to landslides.

The strata began forming 20 million to 100 million years ago by colliding tectonic plates. In a process of repeated collisions and transformations, land mass was pushed upward and cracks dozens of meters deep were formed, which is where rainwater can accumulate.

"The deep-seated landslides were caused as rainwater infiltrated deep cracks over long periods of time," Sassa said. "Similar large-scale collapses may occur when [the strata] absorb large quantities of water."

According to a map of areas that could be hit by deep-seated landslides drawn up by the Land, Infrastructure, Transport and Tourism Ministry in August last year, about 34 percent of the land in Nara Prefecture is at particularly high risk.

The map also indicates the remaining areas of the prefecture and neighboring Wakayama Prefecture are also at high risk of deep-seated landslides.

(Sep. 7, 2011)