I haven't seen any discussions about waterfalls and mountain rivers. So i don't think there would be fluid simulations on a large scale in Thrive, but how do you think that waterfalls and mountain river would works?
- The global world generator would produce a rough map of average elevation, precipitation, etc. - In a particular area (generally whatever the player is looking at), we would generate the actual terrain by putting down river paths, mountain ridges, etc.
To produce waterfalls, we'd simply have a rule where a river going down a steep enough slope could have a waterfall.
The harder step, I think, would be converting this schematic representation into actual terrain meshes. But having the schematic representation is arguably more important for gameplay -- for example, if we decide to place a waterfall on a particular stretch of river, then it's more important that, say, an AI would know that there's a waterfall there, than it is that the waterfall would look pretty.