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[TolyK]

Was reading the FotF (Future of the Fortress) thread and Japa, Kohaku, G-Flex and I kinda got this thought:
how would an underground river get into the surface?

The answer? Cliffs and valleys.

It would be interesting to get cavern life onto the surface (and surface animals into the caverns) through lowering in the surface of the land, i.e. exposed cavern systems showing up in a river valley, or a cave-like entrance on the side of a cliff. This could lead to underground civs actually having access to the surface being more of a norm, and might get some FB's on the surface, for example.

And so on.

This also includes rivers running into mountains (during worldgen) and at least sometimes going underground/going into a cavern. ((Sometimes completely flooded caverns are fun - pumping projects!))

Discuss!

[Greiger]

I too was thinking something like this a few months ago but figured it musta' been mentioned a thousand times in this forum and didn't bother suggesting it.

Seems kinda silly that a river in worldgen when faced with higher terrain and no other path just digs a canyon through it all the time.  Sure it happens in reality, but I imagine that the river would just become subterranean every so often too.  To either pop out farther downstream where the terrain lowers again or to feed into the cavern systems.

Though caverns weren't on my mind at that time those would make sense occasionally having larger surface accesses in areas where the water has worn down the terrain significantly.

[TolyK]

yeah, that too.

[Greiger]

Oops, I remember somebody mentioning rivers in the FotF thread but somehow didn't notice you didn't mention it here, focusing only on caverns...oh well.  Close enough, heh.

EDIT: Added acronym tag to FotF because I like being fancy.

[Girlinhat]

What's FotF?

Also, caves.  I regularly embark on caves, and practically all of them lead to the first cavern layer, and sometimes there's a large pit or a downwards shaft leading into the second or even third cavern.  My first death is always from a trog that comes up through the cave, and on rare times blind cave ogres have come up from the second layer, through the downward passage, through the cave, and right onto my front lawn.  FB also!

[TolyK]

What's FotF?

Also, caves.  I regularly embark on caves, and practically all of them lead to the first cavern layer, and sometimes there's a large pit or a downwards shaft leading into the second or even third cavern.  My first death is always from a trog that comes up through the cave, and on rare times blind cave ogres have come up from the second layer, through the downward passage, through the cave, and right onto my front lawn.  FB also!

Updated OP. FotF=Future of the Fortress.

I sometimes embark on caves too, but those are not very common in good embarks. Having those in, say, river valleys or such would be interesting.

[werechicken]

I think the reason rivers don't run into the caverns is due to flooding issues, although if it's going through a mountain and the cavern is on the same level then that would be pretty cool

[TolyK]

updating OP with info.
hmm, flooding issues...

[Girlinhat]

I upped the number.  50 caves in a pocket region, gives me plenty of options for good cave embarks, and gives a lot of places for an adventurer to hide out during night.  Boogymen don't attack you in a cave.  Advanced World Gen lets you specify cave and mountain-cave numbers.

[Artanis00]

updating OP with info.
hmm, flooding issues...

I think that's more of an issue with the flow algorithm than anything. With the right setup, you could probably build fairly stable water pyramid.

[Bohandas]

I too was thinking something like this a few months ago but figured it musta' been mentioned a thousand times in this forum and didn't bother suggesting it.

Seems kinda silly that a river in worldgen when faced with higher terrain and no other path just digs a canyon through it all the time.  Sure it happens in reality, but I imagine that the river would just become subterranean every so often too.  To either pop out farther downstream where the terrain lowers again or to feed into the cavern systems.

Good point

[TolyK]

updating OP with info.
hmm, flooding issues...

I think that's more of an issue with the flow algorithm than anything. With the right setup, you could probably build fairly stable water pyramid.

yeah, well I think flooding water off-map might not be the ideal choice though (during fort mode) but i guess the flow algorithm should be looked at...

[NW_Kohaku]

I remember someone complaining about this before - basically, local tiles just find the lowest point on the map, and path water to go in that direction, and don't bother to go around cliff faces if they happen to find some. 

(Although I must say I do kind of like having brooks that cut cliffs through hills or mountains, since they tend to make for very easily built and easily defended natural fortresses to just dig down a little, build a drawbridge across the gap, and then build my entire fortress where its only access point is across a drawbridge over running water.)

Anyway, water should simply act more naturally (even if it would take longer to generate a world, but worlds already take so long to generate, I find it's best to just go make a sandwich and come back later) which means that if they hit a low point, they should form a lake, and let the water level rise (probably swallowing up the previous river) until it hits a point higher than the surrounding land and can break over the crest and flow around. 

Underground rivers would basically occur because an aquifer has an "exit point", where it might pop up as a spring, or pour out of a cliff face.  The aquifer would of course be fed by permeable soil that has things like regular rivers or lakes or just basins where rainwater falls.  The difference between an underground river and an aquifer just being that water is actually leaving the aquifer at some point, causing water to rush towards the exit.

[isitanos]

Underground rivers would basically occur because an aquifer has an "exit point", where it might pop up as a spring, or pour out of a cliff face.  The aquifer would of course be fed by permeable soil that has things like regular rivers or lakes or just basins where rainwater falls.  The difference between an underground river and an aquifer just being that water is actually leaving the aquifer at some point, causing water to rush towards the exit.

An aquifer and an underground river are different things though. An aquifer is "drenched stone/soil", while an underground river is actual open, flowing water. Underground rivers are sometimes the cause of huge cave formations, since they form gradually through water infiltration in sedimentary stone, then dig a path, then often dig a new path below or besides the old one, and so on.
The presence of an aquifer can presumably lead to the formation of caves or underground rivers, though. You need rather permeable rock for erosion to occur in the first place.

[Jeoshua]

I remember someone complaining about this before - basically, local tiles just find the lowest point on the map, and path water to go in that direction, and don't bother to go around cliff faces if they happen to find some. 

*raises hand* That was me, I believe.  I remember this very conclusion and talking about it here on the Suggestions forum.

(Although I must say I do kind of like having brooks that cut cliffs through hills or mountains, since they tend to make for very easily built and easily defended natural fortresses to just dig down a little, build a drawbridge across the gap, and then build my entire fortress where its only access point is across a drawbridge over running water.)

It would be nice if it happened occasionally, but as it is now it happens every time two rivers meet.  Plus, in reality, rivers do not cut into mountains the way this game makes them to do.  Look at the Grand Canyon.  VERY tiny river flowing for Eons across a flat expanse, and it caused a HUUUUUGE canyon.  I'd love it if canyons like this were created.  You could have a 4-tile river flowing through a Canyon that takes up a whole embark square, with flat wide banks on either side.  Imagine the kind of fortress you could build on that.

Anyway, water should simply act more naturally (even if it would take longer to generate a world, but worlds already take so long to generate, I find it's best to just go make a sandwich and come back later) which means that if they hit a low point, they should form a lake, and let the water level rise (probably swallowing up the previous river) until it hits a point higher than the surrounding land and can break over the crest and flow around. 

That's a good thought.  Maybe a one-time "water pressure" thing could be checked.  If the pressure is enough to make it rise up one level into an intervening obstacle, then cut through.  Otherwise have the water level rise up at that point until there is either a downward escape for the growing "lake", or the whole map gets filled up, in which case the game says "F*** it" and cuts through the side of the cliff.

Underground rivers would basically occur because an aquifer has an "exit point", where it might pop up as a spring, or pour out of a cliff face.  The aquifer would of course be fed by permeable soil that has things like regular rivers or lakes or just basins where rainwater falls.  The difference between an underground river and an aquifer just being that water is actually leaving the aquifer at some point, causing water to rush towards the exit.

That's what I was thinking about underground rivers, myself.  Basically my though is that if a river source is directly above an aquifer, it should be considered that the aquifer is the source of said river.  Then cut in.  Depending upon the hardness of the rock around, the river banks coming off the sides of the river might follow the flow back into the mountainside, giving you access to the caverns... and those things in the caverns access to the overworld.