Brainstorming River Worldgen

[Perdido Street]

Maybe another approach to generation would be starting with the water-table (the underground plain at which moisture collects because it can descend no further). This, with seasonal variation, usually happens where the deepest soil layers meet bedrock *(though Aquifers -layers of porous Carbonate or Basalt rock types- can also absorb water, and Aquitards -soil rich with clay or too steeply angled- tend to resist absorption).

Since terrain generation already takes into account geology + biome, it should be possible to generalize where its water table forms: in a desert chunk, for example, it would be a single block thick at bedrock level, whereas in a jungle chunk the table could be several blocks tall from bed rock. Any open air spaces that intersect the water table would fill with water (be they caves or river beds).

 

Implementing the water table creates a basis for saying where rivers should start (a chunk with a higher water table abutting a lower elevation chunk). That wouldn't in itself solve the issue of creating realistic erosion paths or consistent volumetrics, but, assuming that (due to gravity) water always wants flow down to be, or fill up to, as close an elevation with the water-table as possible, that provides us a context (alongside knowing what materials form Aquafers vs Aquitards/Can vs can't be easily eroded) for where the river would wear a channel through the land vs where (having reached the local water-table, or erosion resistant barrier) it would spread out into a pond/lake. 

Going further, with the Water table's height tied to seasonal variation (temporarily up during rainy season, or down during a dry spell), it would be possible to simulate flooding and drought. There is already a water saturation mechanic for cropland, by averaging this measure at a chunk/layer level, it could even be possible to track the change in the water-table day by day as a result of rainfall + temperature. (Maybe it's a pipe-dream, but imagine seeing puddles in the ditches after a rainstorm, then watching them vanish as the saturation transfers block layer by layer down to the water table)

Besides its benefit to the river generation project, the water table (specifically being able to dig down to it) is the entire basis of making wells, which would, as is the case in real life, significantly open up inland/dry-region living.

Edited June 2 by Perdido Street
grammar + better explanation

[DeanF]

On 3/26/2026 at 1:38 PM, Bruno Willis said:

I would say, I'm pretty sure rivers almost never split once they start flowing, it's more likely you get streams converging as they flow down hill (which your model also does).

Yes, this is true.  The folks at cartographersguild.com, where they make fictional maps, are quite dedicated about criticizing this mistake.  They call them the River Police.  With extremely rare exception, rivers combine, they don't fork.  Another thing that trips up amateur cartographers for some inexplicable reason is the fact that water flows downhill.  I still get boggled when I see that one violated.

Given the way that VS worldgen proceeds in chunks, I can see a lot of difficulties with generating rivers.  They sort of have to flow downhill, and how can that be predicted for a downstream chunk that hasn't generated yet?  You might have to recreate the whole worldgen process to include an erosion mechanic.  Steal it from a program like Wilbur?.  (Wilbur works by moving voxels downhill scaled for slope and rainfall.)  I suspect that is why all of the mods that add "rivers" result in some pretty odd geography, like holes punched through mountains.  That's just a problem with any game that descends from that other voxel game, y'know?  The basic worldgen that got inherited is problematic.  It really should be erosion-based instead, but crap that's practically starting development over again completely.

The little streams and rivulets that we have now are a lot easier- they just need to end in ponds in low areas instead of magically dissipating.

Edited May 31 by DeanF