Dams for hydroelectric power and other purposes will be further used to prevent floods in case of heavy rain.
This comes in response to the collapse of many riverbanks caused by heavy rain during Typhoon No. 19. The Land, Infrastructure, Transport and Tourism Ministry plans to strengthen its efforts to utilize such dams for flood prevention.
During that typhoon, the volume of water at six flood control dams approached their limits and the operators had to perform an emergency discharge of water. When dams are used for water control, there is the possibility that the water supply will be affected, including for power generation, so the ministry is also considering setting up a system to compensate dam managers for losses.
According to the ministry, across the country there are about 500 dams categorized as class A under state control, which are used for power generation, drinking water and other such purposes. The ministry plans to mainly use hydroelectric power dams for flood control, especially those that are supposed to have a large storage capacity and wide gate for water discharge. When heavy rain is expected, water discharge is carried out in advance to ensure capacity at the time of rainfall.
The utilization of power generation dams for flood control started around 2010. Seven hydroelectric dams in six prefectures, including Hokkaido, Fukushima and Nara prefectures, are currently used for this purpose when needed. Of them, two dams under Electric Power Development Co. (J-Power) in Nara Prefecture discharged water before Typhoon No. 10 hit the area this summer to secure enough capacity to store river water. The water level in the downstream area was about 1.3 meters lower than it would have been if no measures had been taken, and the discharge prevented flooding.
There are 562 flood control dams in Japan. It costs 100 billion yen to 200 billion yen to build one and takes 20 to 30 years to complete. While strengthening the functions of existing flood control dams, the ministry hopes to improve rivers' disaster prevention ability by making effective use of water utilization dams.
The ministry is also investigating the possibility of using hydroelectric dams in the upper reaches of the Chikumagawa river in Nagano Prefecture, where Typhoon No. 19 caused flooding on a grand scale. To encourage electric power companies to cooperate in flood control, the government is considering setting up a system to compensate for losses if the water level drops through the discharge of water in advance.
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