Multiple Aquifer Pierce II: Electric BoogalooAll credit for this idea is due Tanelorn, I've just done my best to spread the idea around and make it common knowledge (along with a bit of testing and a few tweaks).
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 a good bit of wood. At the minimum you'll need enough for one waterwheel and 6 axle segments plus 1 additional axle segment per aquifer level. I'd suggest assuming the worst and keeping more wood on hand for extra axle segments.
At least one unit of stone would be useful, though not necessary, for making a mechanism for a gear assembly and you'll need enough Wood, Stone, Glass, or Metal to build the components for 5 screw pumps (If you have no stone, you'll need enough for 6 screw pumps, one of which will be used to transfer power to a vertical axle in place of the usual gear assembly.)
Lastly, you'll need some material to build 16 walls per level of the aquifer, this can be stone, wood, glass, whatever works, and depending on what sorts of material your aquifers run through, you may be able to recover some of this from the stone left behind as you mine. (but don't count on it).
So in the end you'll need:
12+ wood
5 Blocks (6 if you have no stone)
5 Enormous Corkscrews (Again, 6 if you have no stone)
5 Pipes (Also 6 without stone)
16 Miscellaneous material per aquifer level, for walls.
And if you do have stone, one Stone Mechanism.
Examples provided below use the following:
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
+ = Constructed floor
o = Damp stone
~ = Water filled square
Part I: Preparing to mine and powering the pumpsThe first step is to dig out an up/down stairway into the aquifer, channel out the 4 squares on each side of the stairs from above, like this:
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.........
.........
.........
.........
.........
.........
....H....
...HXH...
....H....
.........
.........
.........
These four channels will allow you to pump out water from around the stairs, giving your miners a place to work from safely on the aquifer level. Before you can begin though, you'll need a power source and a place to pump the water to without flooding your fortress. First, place 4 screw pumps around the stairs in a spiral, like this:
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.........
.........
.........
.........
.........
.....^...
..<@H@...
...HXH...
...@H@>..
...v.....
.........
.........
Then cut a channel in front of each pump, allowing you to pump water back into the aquifer...
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.........
.........
.........
.........
.....H...
.....^...
.H<@H@...
...HXH...
...@H@>H.
...v.....
...H.....
.........
Now you just need a power source. Originally I attached one waterwheel to each pump, and used the flow of the aquifer into the drainage channels to run the wheels, but there were problems piercing multiple aquifer levels using that arrangement. Any power source will do, as long a it supplies sufficient power, but for the purposes of this guide I'm going to use a single waterwheel/screw pump generator nearby. The first step in preparing for this is to cut a channel for the waterwheel like so:
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.........
.........
..HHH....
.........
.....H...
.....^...
.H<@H@...
...HXH...
...@H@>H.
...v.....
...H.....
.........
Then extend one end of the channel by one tile, and add a hook at each end, like this:
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.........
.H..H....
.HHHH....
.........
.....H...
.....^...
.H<@H@...
...HXH...
...@H@>H.
...v.....
...H.....
.........
The hooks will be the input and output tiles for a screw pump driving the waterwheel shortly. (And yes, this is a cheap perpetual motion exploit. For those that find that undwarvenly, well, privately I agree with you. You'll need a nearby river, a windmill farm, or sufficient dwarven labor to provide an alternate supply of power if you choose not to use this trick, and I leave the details of that to you.)
Before you build the waterwheel, you'll need to place the screw pump to support it:
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.........
.H<@H....
.HHHH....
.........
.....H...
.....^...
.H<@H@...
...HXH...
...@H@>H.
...v.....
...H.....
.........
Then you can add the waterwheel and a three tile horizontal axle connecting it to the first screw pump.
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.........
.H<@H....
.HWWW....
...|.....
...|.H...
...|.^...
.H<@H@...
...HXH...
...@H@>H.
...v.....
...H.....
.........
Don't worry if the waterwheel/screw pump kicks on and you start getting some 1/7 or 2/7 water moving around, that's normal, and the aquifer channels will prevent it from flooding, though it's going to get a bit muddy around each screw pump regardless of what you do.
If the pumps don't quite kick in, just run the pump adjacent to the waterwheel manually for a few cycles, and the whole system should kick on. Once you have the waterwheel going, everything should keep moving on it's own.
To power the other three screw pumps, just build three single tile horizontal axles over the "input" channels adjacent to the stairs. These axles won't interfere with the pumps picking up water from below, and they'll transfer power between each of the pumps. When placing a horizontal axle running north/south between two pumps, be sure to to change it's orientation by hitting (s) before placing it. When you're done, you should have something like this, with all four pumps working.
.........
.........
.H<@H....
.HWWW....
...|.....
...|.H...
...|.^...
.H<@-@...
...|XH...
...@-@>H.
...v.....
...H.....
.........
More to follow in Part II: The First Aquifer Level...