Crack open a book sometime,
While you only cracked open the book, I have read them. In fact many.
In fact if you bother to open a history book instead of the comic books you apparently feast upon for your simplistic world view, you'd find that MANY past civilizations have migrated after conditions changed where they were - this was all pre-technology. Bays receded, rivers changed - the story of people migrating to other areas because water has moved is literally as old as recorded history.
Further, it takes a certain level of technology to make use of aquifers - the level of technology that would help to enable a migration... the poor still work off shallow wells or rivers the world over.
Most of the world is unlike the fantasy world you have constructed, people are far more practical and able than you can possible imagine.
Maybe they could move to your backyard. You wouldn't chase them off with a gun or anything, would you?