Footman: " For Lodaerooon!"

Yeah I ended up putting the average height at around 70 and then making the brush a bit smaller and removing about 5 height a couple of times but not below 50. Not as deep as I'd liked but deep enough I suppose.

I assume it a modern age thousands of years after warcraft so the Dalaran hole should be already filled with soil and I never thought to digging one.
If terrain is under sea level water fills in.
If you raise the entire map to 100, and sea level to 90, the hole to 50 it's under sea level anyway.
You can lower the sea and use a bunch of water sources instead, but you have to circle the entire map with terrain so water wont flow out.

Hey Lulu, saw you was working on your version, did you manage to get much of a deep pit for Dalaran Crater? Mine kept accidently filling with water in the earlier pre-finished version.