Work to decommission and dismantle Arase Dam in Yatsushiro, Kumamoto Prefecture, has begun in the nation’s first-ever project to demolish a dam without constructing an alternative facility.
Decommissioning of the dam, which is operated by the Kumamoto prefectural government, started Saturday. It was prompted by local residents’ complaints that the dam worsened the water quality of the Kumagawa river, thereby harming fishery activities.
An increasing number of local residents along the river have voiced expectations that the removal of the dam will restore its clean water. However, it is uncertain whether their hopes will be fulfilled, as there are other dams and weirs both upstream and downstream.
Decommissioning will cost 8.8 billion yen and be completed over 5-1/2 years to March 2018. As this is the first project of its kind in the nation, much attention is focused on how the work will proceed.
On Saturday, 10 workers closed both ends of the dam’s management bridge, which had been also used for residents’ daily traffic. The bridge will be widened for survey and construction vehicles, while the dam’s eight watergates and their pillars will be demolished in phases.
According to a fisheries cooperative headquartered in Yatsushiro, the waters near Arase Dam were once highly productive fishing sites where sweetfish swam up the river.
But catches shrank because sweetfish were blocked at the dam and gravel covered with bog moss, which is food for sweetfish and other fish, did not flow downstream.
Thus the fisheries co-op opposed the renewal of the prefectural government’s water-use rights, which had been held for the dam’s electric power generation, and finally forced the prefectural government to decommission and remove the dam.
Arase Dam was built midstream on the river in 1955 exclusively for power generation. The dam is 210 meters wide and 25 meters high, and can store up to 10.13 million cubic meters of water.
Residents living along the river have complained of the dam’s negative impact on the environment. In 2002, then Kumamoto Governor Yoshiko Shiotani announced the removal of the dam.
Current Governor Ikuo Kabashima overturned Shiotani’s decision at one point, citing the enormous costs of decommissioning, but decided in February 2010 to remove the dam because the prefectural government could not renew its water-use rights.
