I swear I've heard something similar to it in a video by someone like Practical Engineering, but I could be just reading past the typo. Like others said, QC for this chapter was pretty poor.
A river debt (if I remember correctly) is the idea of how much water you remove from the river for agriculture or consumption purposes. It's about how hard you divert water from the main river. In this case I'm assuming the diagram with the reservoir would be to reduce the need to aggressively...
@Ceiye It's very comical, but the humor is super dry. Acquired taste if anything. It's that slight bit of absurdism in the banter that gets me; this manga is really well written.
I wouldn't have the slightest idea what to do with a woman like Yoshino though.