There is a place in Kawasaki where they moved the Hirase river to go through a hill. Where it emerged, there was already a river running perpendicular to the course of the intended path. So, they forced the existing river into an underground pipe that fed to this place, then ran the new river on the new course. You can see it on the map
here. Of course I knew nothing of this when I arrived, and didn't realize that this thing actually has two outlets until I started writing this caption. Not a bad find for an evening's stroll!