Photo/IllutrationYamba Dam at nearly full capacity due to heavy rains brought by Typhoon No. 19 over the weekend, in Naganohara, Gunma Prefecture, at 3:18 p.m. on Oct. 13 (Munetake Tanno)

  • Photo/Illustraion
  • Photo/Illustraion
  • Photo/Illustraion

NAGANOHARA, Gunma Prefecture--Record-breaking rainfall brought by Typhoon No. 19 nearly filled Yamba Dam here overnight from Oct. 12.

The 116-meter-tall dam built by the government has been holding water on an experimental basis on the Agatsumagawa river, upstream of the Tonegawa river, with its completion scheduled for spring.

The multipurpose structure has a storage capacity of 107.5 million cubic meters and will be used for water utilization and control, as well as power generation.

According to the Maebashi Local Meteorological Observatory, the Tashiro district of Tsumagoi village in the prefecture, which is situated upstream of the dam, recorded 442 millimeters of rain, one-third of the annual precipitation, within 48 hours from 6 p.m. on Oct. 11.

About 75 million cubic meters of water flowed into the dam between 2 a.m. on Oct. 11 and 5 a.m. on Oct. 13, according to an announcement by the land ministry, causing the level to rise by 54 meters.

The planned flood storage amount between July 1 and Oct. 5, when precipitation is greater, is 65 million cubic meters, less than the inflow from the typhoon.

Under the water storage trial that started Oct. 1, the water level was expected to reach its limit in about three to four months.

However, the ministry said the dam could become full within a few days if more rain fell in the area.

Had Yamba Dam been in full operation, the space reserved for floodwater storage likely would have been smaller, as the water level would have been raised to hold water for use in downstream areas from Oct. 6.

"If the dam had been in full operation, the excess rainwater may have been released downstream," said river information officer Tadashi Fujita of the ministry's Kanto Regional Developmental Bureau. "The dam had a certain positive effect on water control along the Tonegawa river."

Koichi Mizuide, 65, who runs a restaurant in the Kawarayu district nearby, was astounded by the sight of the nearly full dam.

"It has changed drastically compared to how it looked on the morning of Oct. 12," he said. "If the dam was useful to residents downstream, locals who consented to the dam (being built) can feel rewarded."