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[Notere]

I've spent a few attempts on getting it right thus far, and after another stupid (fun!) mistake in the steps, I finally knuckled down and read the wiki article five times. There's a series of actions requiring flooring over up/down stairs and building the screw pump, then repeating the process on the opposite side. The problem with this is it doesn't account for what floors do to up/down stairs. I'm assuming it hasn't been updated because the steps show the up/down stairs still being there when removing the floor. What I keep seeing in this version is the floor removes the up portion of the stairs, which opens up new problems.

Is there a way around this? A new method? Mostly I just want to get this right and flee the sandy hell in which I am currently trapped. Didn't quite count on the aquifer being the size of the entire map. I mean, it's been fun, but I want some rough gems before a solid dozen dwarves have gone insane from unfilled fey moods and possessions.

[anewaname]

Yep, constructing and then deconstructing the floor will remove the up portion of the stairs, but after you deconstruct the floor, you just construct an up/down stairs on top of the down portion of the original stairs. I'm not sure if it says that in the article, but it works.

[Notere]

After attempting this repeatedly (just in case), designating the stairs for U/D stairs after removing the floor does not work either.

[Hans Lemurson]

Interestingly, with all the different ways I've tried getting through aquifers, I've never actually given the "Double Slit Method" a real try.

Making sure that there is always a path to/from the worksite can be very tricky, since you often have to build and deconstruct things many times.  It's nice when you can preserve the original soil/stone for the staircase, but I often end up with whole layers where I've had to build my Up/Down stairs out of wood.

[Notere]

So if the original soil is destroyed in the process, could I theoretically reconstruct it out of wood? This I am now attempting...

It works. You can construct up/down stairs from wood after the floor destroys the up portion. Thanks for that.

[Sarmatian123]

Double slits is little finicky. It requires little finesse and practice. It looks like this from side:

_<>_ _<>_ <- 2 pump rows from side view, which need to be reversed. The empty space between can be 1+ walls thick, depending on what you are doing. I use personally in each row 3 pumps.

I think the trick was to get the path down, when channeling the 2 levels bellow. I think I used the wall bellow between pump rows somehow for up/down stairs for underground access, instead of messing with walls under pump rows. Just make sure to remove stones and other items from hole first, before using it for dumping water from other side. It should work even in soil just fine.

The thing worth figuring it out with double slit, time after time is... it chews through 10+ levels of aquifer, even in soil, very rapidly. It is extremely safe, when 2-3 pumps in each row are used in comparison to 1 pump. You just need 6 pumping engineers. I go with 10 mechanics for cage traps service and I just enable pumping on them all. It is in borders of their guild profession. Also it does not spam so many cancellation messages.

I was using this method even to dig 3 levels of 11x12 underground mass pit (3 on 3 pits) and mass cancellation messages due constructing in water were noticeable again when clearing aquifer walls 2 spaces further then what double slit is designed for.

You should end on last level of aquifer like this ->

AWAC_XXX_CAWA

, where A-aquifer, W-water, C-constructed wall, X<-constructed up/down stairs, _ channel down.

From above it looks like that: https://imgur.com/a/BFN7tDs

Also I am little confused about checking the level bellow for being aquifer, because if you do it in some peculiar way, you don't need to check it.

For building materials you could use logs or more fancy, but still needing 1 log for 1 block in a process, green glass blocks. I make my pumps always preferably out of green glass, as it is very light pump and can later be used on pumping magma as well. However sand is like flux, sometimes not accessible. You can buy sandbags from caravan for the pumps though. Clay bricks are a fail, as you need 2 logs to make 1 water-safe clay brick.

[Notere]

After working on this for a while, the phrase "your dwarves will start to get pushed around, expect job cancellations" has to be a meme. A fun meme. 3 drownings later, it's legitimately not worth pursuing the method anymore. I don't know how anyone gets this to work once the pump slits start to overflow.

[Hans Lemurson]

It's a very careful dance between leakage rates and drainage rates.  The more aquifer soil you expose, the faster the water pours out.  Pumps can handle a nearly unlimited amount of water, but it still takes time for the expelled water to fall down and get drained away, so you can end up with flooding if you dig too quickly.

The "Double Slit" method is not the easiest method, but it is the one that with the least material requirements.  You have to really understand how aquifers work as a simultaneous "Inifinite Source" and "Infinite Drain", and how water makes things slosh around to understand the how and why of the Double-Slit method.

I've recently experimented with trying to see if I can use water-wheel powered pump-stacks to drill through aquifers without access to stone or metal for mechanisms. (The thread in my sig used mechanisms, and discussion there lead to the creation of the "Double Slit Method"). 

It turns out you can use Screw-Pumps as makeshift gear-boxes to make power turn corners and even connect down to lower levels.  The geometry of an "All-Wooden Pumpstack Drill" however is...complicated (if you want it to be traversible too) and you have to deconstruct and rebuild your pumps after each level in order to remove a floor section to ensure they can connect down below too.

[Notere]

I find that once it comes time to open the center tiles and carve UD stairs for drainage, the entire situation becomes untenable. If the other section is properly walled off on the cardinals and now the diagonals, there's not enough drainage, and overflow is an immediate problem, at which point water starts pushing back to the original side. The volume and violence of the water actually makes it supremely difficult to get anything done. A tile might get mined once a month, but building is just insanely difficult and costs actual lives.

[PatrikLundell]

I suspect you're doing something wrong (see next paragraph), because there isn't that much of an issue if you do it right (and definitely not any overflowing water beyond the occasional wet 1/7 tile). I had to read the instructions several times and follow the instructions religiously step by step to get it working properly for quite a few fortresses before I got the handle on it.

One very important realization is that aquifers do NOT leak diagonally, so you don't dig out the diagonal tiles (which DO leak water diagonally if dug out) to install walls there. If you do that, you're getting the kind of problems with excess water you have, because there are too many exposed aquifer water leaking tiles to handle the drainage.

[Notere]

Yeah. That was sorted out and the latest attempts avoided it entirely.

[Hans Lemurson]

The main trick of the "Double Slit Method" is that when you carve U/D stairs beneath you, you create a drain below which dwarves will not get swept through.  The purpose of the pump is not to allow you to build the retaining walls, but to let you dig the drain beneath.  Once the water is draining below, then you can build the walls in peace.

When you reach bottom, though...that's where the real trickiness is.  Is that the part that has you stuck?

[Sarmatian123]

I tried this method once with 1 pump. I got 3 dwarves killed and job cancellation spam was merciless. All to get through 1 level of aquifer.

Then I got smart. Got 3 pumps on the job and played symmetry game with digging, wall constructing/smoothing.
Then I got even smarter. Got 6 pumps on the job and put the up/down stairs on finished levels between the pumps.

From above it looks like that:

https://imgur.com/a/BFN7tDs

This is also lowest level of aquifer. I am using one side as bottom level of my 2 levels water reservoir for 2 wells way way higher up.

[Notere]

The main trick of the "Double Slit Method" is that when you carve U/D stairs beneath you, you create a drain below which dwarves will not get swept through.  The purpose of the pump is not to allow you to build the retaining walls, but to let you dig the drain beneath.  Once the water is draining below, then you can build the walls in peace.

When you reach bottom, though...that's where the real trickiness is.  Is that the part that has you stuck?

Not really. I suspect, maybe, that the issue was that there was no UD in the other side to act as a drain on the diagonal while working the other side. The bottom, honestly, has nothing to do with anything just yet. Getting one clean setup is the first goal.

[Loci]

The Double-slit method is a well-developed technique that has been used successfully by many players.

The problem with this is it doesn't account for what floors do to up/down stairs. I'm assuming it hasn't been updated because the steps show the up/down stairs still being there when removing the floor. What I keep seeing in this version is the floor removes the up portion of the stairs, which opens up new problems.

Now we need to move the pump onto the other pair of stairs, but must be careful to not lose access to this level from above. We proceed this way:
*Deconstruct the pump and the floor.
*Construct up/down stairs to keep this level accessible. Make sure they connect to other stairs in the level above.

After working on this for a while, the phrase "your dwarves will start to get pushed around, expect job cancellations" has to be a meme. A fun meme. 3 drownings later, it's legitimately not worth pursuing the method anymore. I don't know how anyone gets this to work once the pump slits start to overflow.

The aquifer *should* be draining into the lower level at that point. If your aquifer isn't draining then you didn't follow the directions. Assuming you carved stairs to the level below, that level must not be an aquifer (which should have been indicated by the single-stepping test). If you don't have another aquifer level below you should be performing the "last level" process, not the "upper level" process.

A single orthogonal aquifer tile can absorb *all* water you throw at it; it will *never* overflow.

I suspect, maybe, that the issue was that there was no UD in the other side to act as a drain on the diagonal while working the other side.

Diagonal drains don't work (they block the pressure-teleportation of water), and the double-slit method certainly doesn't use any.