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The , was an earth-fill
On 11 March 2011, the dam failed 20 to 25 minutes after the Tōhoku earthquake as the nearly full reservoir overtopped 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. The failure of the earth-fill dam at the Fujinuma reservoir in Fukushima prefecture resulted in eight deaths in a village.
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
embankment dam
An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil or rock. It has a semi-pervious waterproof natural covering for its surface and ...
in Sukagawa City, Fukushima Prefecture
Fukushima Prefecture (; ja, 福島県, Fukushima-ken, ) is a prefecture of Japan located in the Tōhoku region of Honshu. Fukushima Prefecture has a population of 1,810,286 () and has a geographic area of . Fukushima Prefecture borders Miya ...
, Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. It was established on the Ebana River, a tributary of the Abukuma River, 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 or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. The dam's primary purpose was irrigation. It failed on 11 March 2011 after the 2011 Tōhoku earthquake.
Failure
On 11 March 2011, the dam failed 20 to 25 minutes after the Tōhoku earthquake as the nearly full reservoir overtopped 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. The failure of the earth-fill dam at the Fujinuma reservoir in Fukushima prefecture resulted in eight deaths in a village.
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
Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...
. 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.
Design
The dam was a tall and long embankment-type with a structural volume of and crest width of . About to the south, there is an auxiliary dam with a height of about and length of approximately . 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 drainage area and itsreservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
had a capacity of . The reservoir had a surface area of . The dam was built by Shoji Kensetsu and operated by Ebana River Coastal Reclamation District.
Recovery
Reconstruction of the dam started in October 2013, and has been completed in April 2017.See also
*Dam failure
A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than ...
References
{{Dams in Fukushima Prefecture Dams in Fukushima Prefecture Dam failures in Asia 2011 Tōhoku earthquake and tsunami Dams completed in 1949 Man-made disasters in Japan Buildings damaged by the 2011 Tōhoku earthquake and tsunami