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[smeeprocket]

Okay, so I have another thread going about my quest to capture and breed giant sperm whales as a food source.

I went to build my two level tanks and hit the aquifer on the z level below the beach surface. This is obviously a problem. because I can't use a screwpump to fill the tanks above ground, since the animals I want to trap would not be affected.

I know kind of how to do the double slit method of drilling through an aquifer, though this was my first embark with one and I didn't have to do it.

I need some advice on building larger chambers at aquifer level. Specifically two z levels worth. This also involves things like stairs, and somehow a way to drain the tank. Since it's at the aquifer level, I'm not sure how to do that. I could drain the top room, but it's the bottom room I need drained.

Just checked it again, only two chambers are in the aquifer, but they cover an important area, and I'd like to solve this if possible.

[Absentia]

Aquifers give me a headache. The simplest solution is to cart/pump magma to the surface and use it to cast a nice obsidian ring on the aquifer level.

The other option is to build your ring out of constructed walls, one pumped-out tile at a time. But that's going to take forever if you're building anything large, and you risk drowning your builder(s).

[Panando]

You would need to use drainage from below and it is fairly simple, that is, go under the aquifer using twinslit or whatever, then build a drainage shaft to the map edge (carved fortification), build an off valve (floodgate or hatch) and link it to a lever, and then punch an up/down stairwell into the bottom of tank. You will probably need a larger than 1x1 shaft, probably a 3x3 shaft at minimum - but it only needs to be that wide for 3 z-levels below the aquifer, just enough height to give dwarves access from below.
The tank will continually drain down the shaft allowing you to do some work. Then when work is done, shut of the valve so the tank refills.

Unfortunately, you will not be able to (easily) seal off the shaft at any point above the valve. You might succeed in building a retracting bridge across the shaft (or might not, falling water is tricky), but the moment it is completed it will be thoroughly flooded and you won't be able to link it to a lever or deconstruct it, so if you succeed, you won't have the ability to drain the tank anymore. So this might result in your tank having a deep shaft at the bottom. Might be a problem or might not be.

There is another way, and that is to dig a full size up from the drain (i.e. at least 3-z level below the aquifer, at that point it can narrow down to a 1 tile wide drainage shaft) say you want a 10x10 tank. Dig a 12x12 shaft of up/down stairs from 3z below the aquifer, through the aquifer, to the surface. Then wall off the aquifer on the top 2 z-levels (do this from the top down, to the bottommost level of the aquifer). Once the aquifer has been completely walled off you can floor/bridge off the appropriate level for the desired depth of your tank.
This method works great and I've used it to punch large sealed shafts through aquifers (i.e. for sunlit under aquifer gardens and stuff) and it'll work for a tank in the aquifer too.

[smeeprocket]

right the idea is to go with the pumped out chambers if there's nothing better, but at that size I'm not sure the double slit method can be used as an example. I haven't hit the magma on the map yet, I am recovering from the last goblin siege and a hill titan back to back and I don't want to open that up and have to deal with forgotten beasts, as much fun as magma carting it would be.

Really I don't want to breach below until I annihilate the goblins if ever. Don't get me wrong, my steel industry eats through wood, but my goal is primarily to capture and breed giant sperm whales, and other large aquatic creatures.

thanks Panando, I'll see if I can translate that into action. The second option sounds best since I need to be able to drain the tanks as necessary.

[Absentia]

FWIW, getting to the magma sea isn't really dangerous as long as you seal off any cavern breaches. FBs can't break walls and they don't show up that quickly; the very worst thing you'd have to contend with would be something like a blind cave ogre getting in before you can seal up and even that is highly unlikely, particularly if you're digging near the middle of the map where nothing is going to suddenly spawn.

But I hadn't considered draining from below, which could definitely work. I tend to apply magma to any problem whenever possible.

[smeeprocket]

Both effective automated magma minecarting and playing with aquifers are far more than I have ever attempted before, so either one will probably involve a lot of trial and error. The other problem with the magma minecart is I would probably have to find a spot to punch another hole in the aquifer to get the carts where they need to be, so I might as well just work on drainage efforts. I found a way around the aquifer, but I don't think it's big enough for me to get the series of ramps going that I would need. Though the aquifer is two, maybe three levels deep so it isn't huge.

Okay so at any given time, I will want to be able to drain and fill these tanks. I am guessing I could drain them into the aquifer, and just avoid accidentally draining the entire ocean like that.

God I wish I could squeeze out some more fps, I've used dfhack to clean things up but I am getting maybe 23 fps regularly.

[Panando]

By the way playing with aquifers is safe if you know what you're doing, but it's really easy to make catastrophic errors which can't be recovered from short of using DFHack to plug up the holes with obsidian. An example of a catastrophic error is when one aquifer level drains into another aquifer level in an uncontrolled way, with many opened up aquifer tiles producing water and no way to pump or drain it faster than it's being produced. Methods for penetrating multi-z aquifers are very carefully crafted to have a minimal number of aquifer tiles shedding water at once, even drainage from below depends on having a perfectly vertical column of up/down stairs, and digging it from the bottom up, then sealing the aquifer walls from the top down - do something other than that and you'll get water pooling in places where it causes headaches. Note that normally what makes these errors catastrophic is the FPS hit, if the game was running at a normal speed it'd be merely tedious to recover from the error.

As such I most strongly recommend rolling a quick throwaway game to play around with aquifer concepts (minecarts too). Once all your dwarves have been killed in accidents you can roll another throwaway game . Once you've pulled off the technique in a throwaway game, only then try it for real in a fortress you're actually attached to. Note that DFhack's 'prospect all' command can be used to guestimate the aquifer depth. If you see sandstone or conglomerate or many layers of sand you're practically guaranteed a multi-level deep aquifer.

[smeeprocket]

what I'm going to do is keep a back up copy of my game when I start. I'm not afraid to kill the game and go back some. Maybe I'll play with both techniques while I am at it.

[wuphonsreach]

One guideline for forts in aquifer areas... you can never have enough doors / hatches installed.

At a minimum - hatches every 5th Z level on every single down stairway along with doors around all stairways / ramps.

[smeeprocket]

Well this won't be attached to the actual fort.

These tanks are separate from the fort, areas carved out to trap sea life, which will be released a floor above.