What makes the Ikari and Kawaji dam so special is their interconnecting tunnel that runs through the mountain between them. Through this tunnel, 20 cubic meter per second of water can flow from the Ikari to the Kawaji dam during the rainy season, and 1 cubic meter per second of water can flow in the opposite direction during the dry season. We even got to go inside the tunnel and see the three pumps in action. I asked how the pipes were checked for faults and they are in fact so big they get a yearly visual (humanoid!) inspection on the inside. The smaller pipes are checked only on the outside. A small building adjacent to the Kawaji dam hosted a restaurant and two floors of educational models, videos and pictures of the dam site. These dams are quite close to mount Nantai, near Nikko.
Our second visit took us near an abandoned copper mine. Burning the rocks from the mine had created poisonous gasses that killed many trees on the mountainsides nearby, enabling landslides. It also polluted the river area downstream and greatly affected the rice agriculture. After the mine was closed, many things were improved: sabo works to prevent landslides, replanting the hillsides with trees together with schoolchildren, and a dam to slow water flow. Species that had left the area, such as deer, have returned in recent years.
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