Oh, and I forgot: You can turn off anomalies and surface drifters completely by using the following command:
/worldconfig temporalRifts [off|invisible|visible]
Defines temporal rift behavior (default: visible) Off: No rifts spawn, which also means there will be no surface drifters. Invisible: Rifts are not visible to the player, make no sound and do not affect players in any way, but do spawn drifters. Visible: Rifts are visible to the player, make sound, drain stability on nearby players and spawn drifters.
In your case, I'd go with "off". Underground drifters and other hazards will still exist. And if you want them back, simply use the same command with "visible".
(From the VintageStory Wiki, which I can highly recommend: World Configuration - Vintage Story Wiki)