Fujinuma Dam
Encyclopedia
The , was an earth-fill embankment dam
in Sukagawa City
, Fukushima Prefecture
, Japan
. It was established on the Ebana River, a tributary of the Abukuma River
, 16 km (10 mi) west of the city office of Sukagawa City. Construction on the dam commenced in 1937 and it was completed in 1949 after construction was halted due to World War II
. The dam's primary purpose was irrigation. It failed on 11 March 2011 after the 2011 Tōhoku earthquake
.
On 12 March, 252 dams were inspected and seven dams were found to be damaged. Six embankment dams had shallow cracking on their crests and the reservoir at one concrete gravity dam had a slight slope failure
. Four dams, including the Fujinuma, were inaccessible and could not be inspected.
A preliminary survey of the dam and facilities conducted in April 2011 noted that the breach occurred at the tallest section of the dam. Within the dam's fill, there were layers of organic residual soil that in one area contained a tree stump. The residual soil was used as foundation and in layers as well — above alluvium
. This suggests that the foundation for the dam was not prepared properly, according to the study. In addition, the reservoir's auxiliary dam suffered a severe slope failure
on its upstream face while areas around the rim of the reservoir had mild slope failures or distress. It could not be confirmed whether the earthquake or a quick draining of the reservoir was the cause of this.
had a capacity of 1504000 cubic metre. The reservoir had a surface area of 20 ha (49 acre). The dam was built by Shoji Kensetsu and operated by Ebana River Coastal Reclamation District.
Embankment dam
An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof...
in Sukagawa City
Sukagawa, Fukushima
is a city located in the center of Fukushima, Japan. It is famous for both its peony garden , a national scenic beauty, and its torch festival which has been hereditary for over 400 years....
, Fukushima Prefecture
Fukushima Prefecture
is a prefecture of Japan located in the Tōhoku region on the island of Honshu. The capital is the city of Fukushima.-History:Until the Meiji Restoration, the area of Fukushima prefecture was known as Mutsu Province....
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. It was established on the Ebana River, a tributary of the Abukuma River
Abukuma River
The , with a length of 234 km, is the second longest river in the Tōhoku region of Japan and the 6th longest river in Japan. It runs through Fukushima Prefecture and Miyagi Prefecture, rising from springs in the peaks of the Nasu Mountains, collecting water from tributaries leaving the Ōu Mountains...
, 16 km (10 mi) west of the city office of Sukagawa City. Construction on the dam commenced in 1937 and it was completed in 1949 after construction was halted due to World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. The dam's primary purpose was irrigation. It failed on 11 March 2011 after the 2011 Tōhoku earthquake
2011 Tōhoku earthquake and tsunami
The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east...
.
Failure
On 11 March 2011, the dam failed 20 to 25 minutes after the Tōhoku earthquake as the nearly full reservoir over-topped the dam's crest. Locals reported hearing a loud burst before seeing a flood. The flood washed away five houses while damaging others, disabling a bridge and blocked roads with debris. Eight people were missing and four bodies were discovered after searches began at dawn.On 12 March, 252 dams were inspected and seven dams were found to be damaged. Six embankment dams had shallow cracking on their crests and the reservoir at one concrete gravity dam had a slight slope failure
Slope stability
The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock...
. Four dams, including the Fujinuma, were inaccessible and could not be inspected.
A preliminary survey of the dam and facilities conducted in April 2011 noted that the breach occurred at the tallest section of the dam. Within the dam's fill, there were layers of organic residual soil that in one area contained a tree stump. The residual soil was used as foundation and in layers as well — above alluvium
Alluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
. This suggests that the foundation for the dam was not prepared properly, according to the study. In addition, the reservoir's auxiliary dam suffered a severe slope failure
Slope stability
The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock...
on its upstream face while areas around the rim of the reservoir had mild slope failures or distress. It could not be confirmed whether the earthquake or a quick draining of the reservoir was the cause of this.
Design
The dam was a 18.5 m (61 ft) tall and 133 m (436 ft) long embankment-type with a structural volume of 99000 cubic metre and crest width of 6 m (20 ft). About 300 m (984 ft) to the south, there is an auxiliary dam with a height of about 6 m (20 ft) and length of approximately 60 m (197 ft). The auxiliary dam helped the reservoir maintain it designed levels given the topography wouldn't allow the single main dam to do so. The dam sat at the head of a 8.8 km² (3 sq mi) drainage area and its reservoirReservoir
A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...
had a capacity of 1504000 cubic metre. The reservoir had a surface area of 20 ha (49 acre). The dam was built by Shoji Kensetsu and operated by Ebana River Coastal Reclamation District.