It's against code to do anything that would divert rainwater to another property causing damages. Might be able to get him that way.
https://www.nolo.com/legal-encyclopedia/neighbor-disputes-over-water-damage-29724.html
this is what i was thinking. And the city might also have some thoughts on diverting drainage if it starts to adversely affect its properties (i.e. dragging gravel or channeling, etc)