!WARNING! Mistakes were found in this arrangement, I'm revising it and posting an updated version on page 2, please do not use this version for piercing multiple aquifers. All mistakes were my own, and all credit is due Tanelorn for the original idea on how to pierce multiple aquifer layers in a minimal amount of space.
It's possible to drill down through any number of aquifer layers, if you're careful, without needing any extra space on each level. You'll need some wood and glass if you have access to it, to make mechanisms. Without glass, you'll need at least enough stone to make the mechanisms for four screw pumps and (possibly) some gears. To begin with, I should say this idea isn't mine, I tweaked it a bit to make it work for what I needed, but the basic idea came from someone else (unfortunately I can't remember who it was, or I'd give credit where credit is due). (Edit: Found it, the original idea came from Tanelorn.)
X = up/down stairway
H = Channel
* = Gearbox
@> = pump, with water pumping in the direction of the arrow/caret
- | = horizontal axles
WWW = water wheel
. = empty square
o = Damp Stone
~ = Water filled square
To start with you need to cut a stairway down into the aquifer, then channel out the a square on each side of the stairway from above, like this...
.....
..H..
.HXH.
..H..
.....
These four channels will allow you to pump out water from around the stairs, giving your miners a place to stand while working on the aquifer level. Before you get to that though, you need a place to pump the water to, and a power source. The way I usually do it is to place the pumps like this...
.......
....^..
.<@H@..
..HXH..
..@H@>.
..v....
.......
Then cut a channel in front of each pump, allowing the water to drop back into the aquifer.
....H..
....^..
H<@H@..
..HXH..
..@H@>H
..v....
..H....
Now you just need a power source, I attach one waterwheel to each pump, and use the flow of the aquifer into the drainage channels to run the wheels, which, admittedly, is a bit
excessive dwarfish, but the extra power can be useful running whatever you need later on, and it saves on gearboxes, which depending on what sort of terrain you have access to, may be hard to manufacture.
I usually lay them out like this...
...........
..WWW......
...|..H..W.
...|..^--W.
..H<@H@..W.
....HXH....
.W..@H@>H..
.W--v..|...
.W..H..|...
......WWW..
...........
When you're ready to go, just channel out the tile separating each water wheel from the pumps drainage channel, like so.
...........
..WWWH.....
...|..H..W.
...|..^--W.
..H<@H@..W.
.H..HXH..H.
.W..@H@>H..
.W--v..|...
.W..H..|...
.....HWWW..
...........
If one of the pumps doesn't quite kick in, just run it manually for a few cycles, once the whole system is going the waterwheels should keep moving on their own.
Ok, deep breath. So the setup is a bit complex, but once you have your waterwheels in place, you can start drilling. Please be sure to save first! I haven't lost a miner doing this, yet, and if you do each step exactly this way you
shouldn't either, but it's seemed close a few times, so be careful about it.
Once you're ready to start drilling, drop down to the aquifer level, and you'll see this...
ooooooooooo
oo~~~~ooooo
oooooo~oo~o
ooooooooo~o
oo~oo.ooo~o
o~oo.X.oo~o
o~ooo.oo~oo
o~ooooooooo
o~oo~oooooo
ooooo~~~~oo
ooooooooooo
The tiles just on either side of the stairs might have 1-3 water in them, and will fluctuate around there as the pumps above drain the water coming in from the aquifer away, but they should be safe to work on. If you didn't use an up/down stairway, cut a down stairway now to get a look at the next level. Every aquifer level you cut through will be the same, except the last one. On the last level you just need to wall in the 4 squares next to the stairs and then continue down at least one level before you cut out to the sides. If you don't notice you're on the last aquifer level you may inadvertently flood the level below, making it more difficult to proceed, so always check first.
Assuming there is another aquifer layer below, begin by channeling eight tiles away, as follows:
ooooooooooo
oo~~~~ooooo
oooooo~oo~o
ooooHHooo~o
oo~oo.oHo~o
o~oH.X.Ho~o
o~oHo.oo~oo
o~oooHHoooo
o~oo~oooooo
ooooo~~~~oo
ooooooooooo
Now dig out the 4 tiles that are diagonal from the stairs, like so..
ooooooooooo
oo~~~~ooooo
oooooo~oo~o
ooooHHooo~o
oo~o...Ho~o
o~oH.X.Ho~o
o~oH...o~oo
o~oooHHoooo
o~oo~oooooo
ooooo~~~~oo
ooooooooooo
And channel out 4 more tiles, extending the trenches you've already dug like so...
ooooooooooo
oo~~~~ooooo
oooooo~oo~o
oooHHHoHo~o
oo~o...Ho~o
o~oH.X.Ho~o
o~oH...o~oo
o~oHoHHHooo
o~oo~oooooo
ooooo~~~~oo
ooooooooooo
Now this next part seems to be the mildly dangerous one. One at a time, digg out the 4 remaining tiles bordering the central stairs area. This will give you access to the square immediately below where each pump drains, so go ahead and cut a channel down to the next aquifer layer, when you're done, you should have this.
ooooooooooo
oo~~~~ooooo
ooooooHoo~o
oooHHH.Ho~o
ooH....Ho~o
o~oH.X.Ho~o
o~oH....Hoo
o~oH.HHHooo
o~ooHoooooo
ooooo~~~~oo
ooooooooooo
You'll get a rush of water each time, and if you have multiple miners working below one may be accidentally swept into the aquifer, so take your time and do each tile individually. Once you have the channels cut though, the center section should no longer be receiving water from the aquifer, since aquifer tiles don't fill nearby tiles with water diagonally.
To pierce another aquifer level, just disassemble the pumps above, cut a channel through the floor at the end of each axle, then build 4 gearboxes over the channels, and reassemble the pumps on the first aquifer level. With the pumps in place on the aquifer level just channel out the 4 tiles around the stairs, feeding the pumps. When you're done, you should have the following...
Waterwheel Level: Aquifer level:
........... ooooooooooo
..WWWH..... oo~~~~ooooo
...|..H..W. ooooooHoo~o
...|..*--W. oooHHH^Ho~o
..H*.H...W. ooH<@H@Ho~o
.H..HXH..H. o~oHHXHHo~o
.W...H.*H.. o~oH@H@>Hoo
.W--*..|... o~oHvHHHooo
.W..H..|... o~ooHoooooo
.....HWWW.. ooooo~~~~oo
........... ooooooooooo
From there, just repeat everything one level down. You'll need to add a vertical axle for each pump if you have more than two aquifer levels to punch through.
Again.. on the last aquifer level, just wall in the 4 squares around the stairs and leave at least one dry level between you and the aquifer.