William The new Tateno Dam is what is known as a “running water” dam (流水型ダム, ryūsui-gata damu) - that is, the three outlets at its base are kept open permanently, and the damn serves simply to control water flow. However, in the event of a “150 year flood” event, the reservoir may fill entirely, so the dam is designed to allow water to flow over its top. To test this functionality, recently engineers blocked the lower outlets to force an overflow. JR had arranged a special sightseeing train for tourists to witness this once-in-a-lifetime spectacle. The photos are certainly alarming - hopefully, we will never have to see this occur naturally. Yomiuri has the scoop (Japanese),; photo from the Kumanichi. https://www.yomiuri.co.jp/local/kumamoto/news/20240205-OYTNT50172/