When you put your tile in, you most likely sized it to accomodate whatever water was needed to be drained from your property, including any water coming from his ground.

If he concentrates his water into a tile that dumps at your fence line, and his tile is draining more acres than what was coming across the fence at that location before he tiled,
you have a case for not allowing him to dump the new tile at his fence.

The law is that one cannot avoid taking the water that was there before.

Might be difficult to prove-------- but I would guess that drainage guys do the calculations every day when laying out tile patterns.