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[WanderingKid]

So I tried something new and went after a site with a huge Aquifer... there's one in all three biomes on my embark.  I'm double slitting through so that's not a huge concern since I've got tons of wood and it's apparently only 2 layers deep.

However, I was wondering if anyone has ever found a successful way to mine out a seam in the aquifer layer?  It'll be a while before I dig for magma and a coal seam (or 10) would be really nice to have.  If the seam was at the top layer I could probably just channel it but it's in the second layer, and digging 'up' into an aquifer along a seam just seems silly... amusingly FUN, but silly.

[Pootis]

Unless you want to use pumps, I don't know of any way, and with the way aquifers are now pumping it out seems like too much trouble just for part of a coal seam.

If groundwater was implemented so that you'd get a much more gradual, realistic flooding then it'd be different.
Sorry.

[Sutremaine]

Since you've gotten through the aquifer, you could try bringing magma up and rebreaking the aquifer in the same way that you would on a freezing biome, creating an open quarry.

[WanderingKid]

Since you've gotten through the aquifer, you could try bringing magma up and rebreaking the aquifer in the same way that you would on a freezing biome, creating an open quarry.

Not quite sure what you mean there, Sutremaine. Why is Magma important in this case?

[Sutremaine]

To seal off the edges of the dig area. On a freezing biome, the aquifer water turns to ice as soon as it's exposed to air, holding the aquifer water at bay. Casting obsidian will have roughly the same effect. Then you can make stairs out of the first layer, pump it out (the stairs will no longer be able to produce water, and the water from the edges of the pit can't get past the obsidian), and move onto the next layer.

You'd need to do a lot of digging to get all the coal seams, and your energy may be better spent creating a tree farm. If your aim is fuel and not carbon, digging for magma would be even better.

[WanderingKid]

Ahhh!  Okay, now I get you.  Yeah, it's mostly as a fuel source.  I made a mistake breaching the aquifer thinking I could use the pumpers to dig a bit of the coal loose and... errr... yeah.  It's gotten interesting.  I may end up digging another ditch for pumping into because of a single extra dig point.

Ah well, my own fault.

Thanks for the idea, but yeah, once I hit magma I won't need most of the coal.

[laularukyrumo]

It'll take you a long, long time to do this, and require several pumps, some careful planning, and probably either a source of clay or enough stone blocks that you don't mind missing, but.... you CAN dig out the edges of the map, build walls (or exploity raised bridges) at the extent of the map edge permitted, and then once you've surrounded the entire z-level with walls, strip mine the entire level. Once you mine out a tile, it can't produce water anymore, ever. If you do this, I highly, HIGHLY recommend you pick a few portions of the aquifer and leave them unmined, and just surround them with walls. Having an infinite source of water, as well as an infinite drain, is incredibly useful for various projects--especially obsidian farming.

Alternatively, just go get magma. It won't help you make steel, but you can burn trees for that. If you're willing to go to the trouble of building a magma pump stack, you can use the magma to cast obsidian over the aquifer and then dig that out.

If you have multiple z-levels of aquifer, it's possible to strip mine the entire z-level and make it drain into the level below it. It'll take you a long, long time, though.

[vanatteveldt]

This won't be easy, but I think you can you completely drain and strip mine the aquifer by

#1 prepare a drain on the z level below to the map edge
#2 dig a channel around the zone you want to mine. First level can drain into the second level (just like with the slit method), second level can drain into the map edge. Build/smooth walls around the mining zone
#3 Completely channel out the first level. It should drain into the slit and off the map. Once the level is gone no more water is created inside the enclosure
#4 Channel out the second level. The water will drain into the prepared drain.

Mind you, I've not tried this, but it would be nice to test this on a small (say 7x7) square and see how easy it is to extend...

You could even try not walling it off and just letting it drain permanently, also a nice source of power / waterfalls and you could build your entire fortress within the drain zone and have a permanent waterfall all around the fortress. Pretty bad for FPS but good for megaconstruction bonus points :-)

[kingubu]

I have a method for digging out large areas in aquifer by dropping the water with up/down stairs.  But only if there's more than one layer with aquifers.  And you can only mine the upper layers.

Dig a channel and down stair two squares apart and put a pump between them.  Hmm, let me make some screenies.
Pump

Start the pump and dig up/down stairs around the ramp and up/down stairs on the layer below to drain.  One at a time N,S,E,W, then the corners and get this.

And below

From here you can turn off the pump and just dig up/down stairs in all directions till you get bored.
It's best to designate every other stair and the stair below it.  Like this.

If you only designate the walls and right below you never get "damp stone" warning because you can already see it's aquifer before you dig.
And we're done.  Big room in the aquifer.  This took about two weeks.

If it's more than 2z's of aquifer, it's best to keep the room small and go down to the bottom layer, then expand out from there.
Rebuilding the pump and channel on each floor down I'll leave as an exercise for the reader. 

Edit:  Woops, late night posting strikes again.  As soon as I posted I noticed you said coal is in the bottom half.  So all this is useless to you.
I had a similar problem with iron only being inside the aquifer layer in my fort and had to do this to get to it.
But mine was 6z deep, so I was only sacrificing 1/6 of the iron to get to the rest of it.

[kingubu]

After some thought I decided to try to drop the bottom out of the big room.
Dug a drain 2z below the aquifer.

And walled off the second to the bottom layer and built some pumps to make a dry spot to start draining.

  Probably should have built those in two rows facing each other north and south.
Dug three drain holes up from the bottom.  Two by the pump outlets to give the water some place to go, otherwise the water just splashes around and pushes the pumpers off the pumps, I've learned from previous attempts.  And one by the pump inlets to help dropping the water enough to work.

  Could only dig three starter holes because I only had three starting miners.  The water dropping through makes it impossible to dig more than one time before they have to flee.

  Fortunately, the first wave of migrants arrived in time to work the pumps.  I started digging a 3x3 in the stone under the aquifer and expanded outwards from there one row at a time.
Once all the drain stairs were dug, it was trivial to wall the last aquifer wall.  No cancellations at all.

  In retrospect, it probably would have been faster to dig a smaller room and a smaller drain then expand it.  And I have a thought that pumping the edge out first instead of the center might work better, but I'm tired so that may be nonsense.

[WanderingKid]

I appreciate the thoughts, Kingubu.  I'll have to try them out if I get the chance, but this fort is about to go down in flames fun.  The aquifer I'm dealing with is spastic.  It's inconsitent as to when a material is an aquifer block so even over-pumping areas just jams up some of the drainage areas, I've got layers in the middle of the aquifer that aren't aquifers (gypsum/very fat coal veins), and I royally banged up trying to get the level I'm working on done when I tried to make some 'shortcuts' to the doubleslit after I was 10 levels down and still going. 

As an example, I've got one layer... you know, a screenshot makes this easier.  Before you read them understand that after I removed the composite I didn't realize the Kaolinite was also aquifer capable, so I thought I was done flooding that area and was prepping to move down.




Because of all the time I spent fighting with it... I never got around to arming my dorfs or getting up defenses, and an ambush just landed when the last migrant wave of nearly 30 dwarves pushed me over 80.  My own fault (kept waiting for stone/metal), but it's not going to help matters.

One odd thing I found was that you don't want to try to double-pump from the same source square.  It doesn't end well.

So, I appreciate all the help.  Depending on what happens during this raid (it appears I've also got a siege coming, a force of vile darkness) will depend on if I can even recover from this.  But it will hopefully help for next time.

EDIT: Screwed up my links.

[laularukyrumo]

Important information for your future: Kaolinite does not, in fact, support aquifer. What you're seeing is the aquifer on the z-level above. While aquifer tiles don't spew water vertically upward, they DO leak on the z-level below. So, y'know, be careful of that.

[WanderingKid]

Important information for your future: Kaolinite does not, in fact, support aquifer. What you're seeing is the aquifer on the z-level above. While aquifer tiles don't spew water vertically upward, they DO leak on the z-level below. So, y'know, be careful of that.

RAZZLEFRAGGLESOGGYSAUCEPANTS!

Errr, um... thank you for that.  I'll correct some things immediately.