Kirk here. In a comment I’ll put a link to this video showing how Shimotori flooded yesterday. It was particularly sad for folks with shops below street level. :(
Fun fact: When Kato Kiyomasa built the castle, the Shirakawa flowed through this part of town. After he used the river to carry all those heavy boulders to the construction site, Kiyomasa diverted the flow, producing the state we know today. The diversion of the river was very successful and invaluable to the building of what we now know as downtown Kumamoto. But, even Kyomasa couldn’t change the fact that Shimotori used to be a riverbed and, as such, is subject to flooding at times like this. Next time you walk down Shimotori look around and imagine how the street used to be a river. :)