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[Jeoshua]

My suggestion for the next (or near future) release of Dwarf fortress is:

Have rivers not run uphill... not cut through sheer cliff faces because they can't run up-hill.  I know it would take more processor power to more accurately simulate where the rivers are going, but it's really only once that they need to be generated... I've grown very tired of seeing 15z sheer canyon walls on EVERY river, stream, and brook that goes through the high drainage areas on my maps.

It seems to me the algorithm used for river flows is similar to the one used for drainage: Take a 3x3 grid from the region map, Find the high area and the low area, then run a river in the center area that connects those regions.  It works well enough, but when you're dealing with a map that is not just 16x but (16x48=) 768x more complex than that, it just doesn't look right anymore.  And you get the weird rivers that seem to plow right through anything they touch, uphill or not.

Instead, what if DF took a moment and generated a height map for the top Z layer AS IT WOULD BE SEEN IN ADVENTURE/FORTRESS mode, then ran the rivers downhill on that (ONLY ever downhill or straight ahead, never up-hill even one Z, please!).  Then at the bottom of drainage pits, it could form lakes (as it does now).  Once the lake fills up to a certain point, it could spill over and start flowing downhill again.  This might cause rivers to "back up" and widen out, too... which would be very awesome for lakes to do.

Then once the hydrosphere is set up, the erosion calculations could be computed... and then back to running the rivers downhill again.  This could start over from brooks only, or maybe river sources only.  The water would flow downhill again, and this time take a slightly different path due to the terrain being eroded a bit.  The key here is there should be a maximum of erosion possible.  Rivers should NEVER be able to cut into hard rocks.  It should be computationally trivial to figure out how much sediment is there.

Anyways, that's my 2 bits.  But it seems, Oh Toady One... that you are very much into depth of realism for the worlds your program creates, and in my opinion the hydrological systems need quite a bit of work in the world-gen aspect.  Thank you for your time.

[ikkonoishi]

Rivers don't run uphill. They run downhill, and wear away the cliff where they fall. Eventually they form a canyon.

[forsaken1111]

Rivers don't run uphill. They run downhill, and wear away the cliff where they fall. Eventually they form a canyon.

That is true in real life, not so much in DF. Oh and thanks for linking to canyons, I had no idea what one was. 

[zwei]

Rivers don't run uphill. They run downhill, and wear away the cliff where they fall. Eventually they form a canyon.

Problem is that DF rivers sometimes run such way that they would have had ran uphill to form canyons we see ingame. Sometimes they split hill in half.

[Max White]

Ok, this is understandable. A quick search will not bring this thread up, so it's not your fault for not knowing about it, but we have some what of a water megathread. It includes this suggestion with many others.
http://www.bay12forums.com/smf/index.php?topic=39662.msg681877#msg681877

[blizzerd]

there is one other way rivers can create canyons that could explain it to be seemingly running uphil before it cuts the canyon

sometimes underground rivers run over plateaus of impenetrable rock with soft rock on top of it, a hill can be on top of this river as long as the flow underground goes down overall (due to pressure and suction it can even be going up small parts) then when the river starts cutting in the sides of the soft rock the layers above slowly crumble down, untill the underground river becomes open, and seemingly has cut a canyon straight trough a hill or even small mountain

[Draco18s]

there is one other way rivers can create canyons that could explain it to be seemingly running uphil before it cuts the canyon

That's great and all, but I somehow doubt that every river ever does that.  In DF it's the defacto standard.

[Jeoshua]

I realize this must have been brought up time and time again, but like many suggestions it gets buried under a mountain of "oh and I would like this, too".  I figured this suggestion, as irking as it is to me, should get it's own category.

I did find a partial workaround, tho.  If you set the number of rivers in worldgen to a high number, say 800, then the number of rivers AFTER erosion to a lower number, along with a low erosion count, DF seems to cull the rivers that make little sense.  The erosion still happens, but one is left with dry canyons instead of rivers cutting across every hill.