Extreme-flood control operation of dams in Japan
Ryota Nakamura, Yukihiro SHIMATANI
Abstract
Japan In Japan, floods exceeding the flood control plan by dams have become more frequent in recent years. When such a flood occurs, the reservoir is operated to discharge the same amount of flood as the inflow, which is called "Extreme Flood Control Operations". Therefore, knowing the implementation of Extreme Flood Control Operations is equivalent to knowing the scale and frequency of extreme flood events in Japan. The number of Extreme Flood Control Operations is expected to increase due to climate change, which provides a current assessment of the impacts of climate change. In Japan, the number of Extreme Flood Control Operations has been increasing between 1960 and 2019. However, the number of dams being built is increasing, and the number of Extreme Flood Control Operations per dam construction is decreasing. In more than one case (41 %) of the floods that were operated to prevent extreme floods, the capacity of the dam (the sum of the flood control capacity and the diversion capacity) was required to exceed the storage capacity of the dam. This means that there are some floods that cannot be handled by pre-flooding to ensure flood control capacity. Therefore, it is suggested that dams alone cannot cope with increasingly severe floods in the future.