I accidentally flooded levels 42, 41, and 40 of my Fortress, and I don't know how to stop this mess. No dwarf is going to build a wall, a floodgate, a channel, or a floor where there is water, even if it is just 1 level of water. So I don't see an obvious way of shutting off the stairs and limiting the flooding to the original level (42).

If I can manage to limit the flood to level 42, then it will be much, much easier to tackle. Which is a good way to stop this flooding?

Version: 0.50 (Steam).


One dumb Miner did not notice that the wall was damp, struck the Pickaxe there, and released all of one underground river's destructive power into my Fortress:


The water is going downstairs and flooding everything else below it:

Elevation 42 screenshot

Elevation 41 escreenshot

Elevation 40 screenshot


Elevation 43. I cannot channel on the border of the map, so CAVE-IN, is not an option.

enter image description here

  • I wonder if this helps? gaming.stackexchange.com/questions/396310/…
    – Timmy Jim
    Apr 24, 2023 at 20:01
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    @TimmyJim I've tried to figure out what the heck is that before asking, but I don't understand about the ASCII version, as I'm playing the Premium version. Apr 24, 2023 at 20:02
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    You can switch Steam version to ASCII too. Apr 25, 2023 at 20:32
  • @Revolver_Ocelot I played the ASCII version before the Steam version. The ASCII version was what made me pay for the graphical one, because the ASCII is impossible to decipher. I would never turn the paid game to ASCII. That would not be sane. Apr 26, 2023 at 0:45
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    Re: "did not notice that the wall was damp", in case you weren't aware, dig cancellations only happen when a previously hidden tile is revealed. If the damp tile was already visible (as banks of known rivers usually are) when you designate, DF assumes you deliberately meant to dig it out. (e.g. in case you intentionally want to flood something)
    – R.M.
    Apr 26, 2023 at 18:34

3 Answers 3


As this is underground you should be able to put a plug close to where the initial breach of the underground river happened. You are doing a slightly simplified version of what is described in the wiki article "Aquifer", section "Exploiting Cave-Ins". You dig around a plug that consists of several fields of solid rock and then let these drop from above into the channel north of the river. This works because on the top level of the underground river, you can safely access the water from above.

If this is successful you only have a finite amount of water left in your fortress. You can either spread it out over a large enough area that it will eventually evaporate (note that this will leave soil where underground plants can grow) or you can drain it into some hole where it doesn't disturb you.

Edit: More details on the plug. The actual plug will be a chunck of rock in its original state. For a plug a 1x1x1 block is enough, for aquifier piercing you need something bigger. To make the plug fall into the river you need to dig out every block around it in all three dimensions. So you will dig out a 3x3x3 segment of rock minus the central cube which will form your actual plug. The central block needs to be directly above the river and will fall (at least) two levels when you set it loose. For the two higher levels you first mine them out and the channel into the ground to free the plug on all sides. You need to plan ahead a bit so no dwarf gets injured from falling, gets stuck in the hole or has the plug fall on their head.

Edit 2: per qazmlpok's comment it is probably enough to dig out only the directly adjacent blocks to your plug (in all 6 cardinal direction). This requires a less space but the general idea is the same.

  • Is this what you mean? That I should go up ONE level, to Level 43; then channel around ONE tile that is exactly on top of the ONE tile that I want to shut off on the Level 42 below; and watch the ONE tile fall and shut off the ONE tile that leaks the underground river? Apr 25, 2023 at 19:02
  • @BsAxUbx5KoQDEpCAqSffwGy554PSah You also need to mine out the tile above that block, i.e. on Level 44. The goal is to have a block of unmined stone that is not connected to any walls/floors - on the four cardinal directions, and also top/bottom. Bottom is already taken care of. That will cause a cavein.
    – qazmlpok
    Apr 25, 2023 at 22:08
  • @qazmlpok Sorry, but I did not understand why Level 44 needs to be involved. The tunnel that was dug into the underground river is just one block tall. Apr 26, 2023 at 0:47
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    tiles are "attached" at their top, too. you need to remove that, too to force it to fall down since it would be a "stalagmite" otherwise @BsAxUbx5KoQDEpCAqSffwGy554PSah
    – masterX244
    Apr 26, 2023 at 8:48
  • Cave in will not work here, unfortunately. The "underground river" is, in fact, the bottom of an over-the-ground river. But the tunnel is so near the border of the map that I cannot channel around the ONE tile that I wanted to cave in. Apr 26, 2023 at 14:05

Disclaimer: Much of this is theoretical, as I've never had to actually deal with a massive flooding event. Some of my knowledge is also out of date; I've never run into an underground river before. I'm assuming that they function like an overground river or an aquifer, i.e. they produce an infinite amount of unpressurized water.

The first step is to seal off the water as much as you can. Forbid any doors that are in its path - doors are waterproof until they're opened. Forbidden doors are locked and can't be opened, so they'll act as a seal. Just make sure you don't lock anyone in.

You should be able to place constructions up to a depth of 3 units. It looks like the water is slowly expanding, so you should be able to still add doors to 1-2 depth areas. If you have narrow corridors, place doors in them to block the water and forbid them. Make two layers, just in case something goes wrong. If not, then just use walls. Doors are suggested simply because they're lighter than raw stone and usually plentiful.

There are two ways to remove water:

  1. Pump it back into a source of water (I can't guarantee this works for an underground river; it will not work for a light aquifer or for any finite source of water)
  2. Let it evaporate. Water at 1/7 depth will eventually disappear on its own. If you seal off the breach, eventually all the water will settle and evaporate from the top. This won't remove any water that has pooled into lower areas, but you can use pumps to pull this water out into a wider area where it can evaporate.

To pump the water out:

  1. Excavate the area directly above the breach: You need a channel over the breached area you want to reclaim, and another channel over the underground river.
  2. For maximum safety, place floor grates over both channeled areas, and add doors to ensure water cannot escape. Water can travel through grates, even through a pump, but dwarves cannot. Just in case I'm wrong about how pressurized water works here.
  3. Build a pump over the breached area. Have it set up so the pumped water follows a narrow corridor into the other channeled area - in other words, pump the water back into the river.
  4. An infinite source of water also acts as an infinite reservoir, so this should result in the pumped water being removed. Pumps pump faster than unpressurized water travels, so this will prevent any further water coming out, and will pick up the water that had already escaped.
  5. Once the water drains and goes under 3/7 past the pump, you should be able to install doors, actual flood gates, or walls just past the pumped area, and thus permanently seal it off, at the source.

This will not recover any flooded lower areas, but you can just install a pump on top of another channeled area and pump it into a larger area. This water will then settle to 1/7 and evaporate. Slowly, but it's going to be easier than trying to work it back into the underground river.

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    Since it is underground, an alternative to placing constructions would be dropping stone from above to block the water off. It's more complicated, but should work regardless of how much water there is.
    – Odalrick
    Apr 25, 2023 at 9:59
  • "Forbid any doors that are in its path" There is none. Sorry if the screenshots did not make this clear. Apr 25, 2023 at 18:54
  • "You should be able to place constructions up to a depth of 3 units." The screenshot "Elevation 42" shows that I ordered construction of a wall just after the Stairs, to shut it off, but construction was canceled due to water existing there. And, since it is beside a depth of 4 units, then it must be at a depth of 3 units. And could not be built. Apr 25, 2023 at 19:05
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    @BsAxUbx5KoQDEpCAqSffwGy554PSah water levels are constantly changing. Right now its depth might be 3, but it could be 4 on farame before that, and that would be enough to stop the construction. One attempt at salvaging this might be attempts to install as many doors as you can in not-yet-flooded hallways. If that fails... Well, losing is fun, and you will learn to better water-proof your fortress in the future. Apr 25, 2023 at 20:37
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    @BsAxUbx5KoQDEpCAqSffwGy554PSah: Although, IIRC, a dwarf crossing through the door can lead to the situation where the water rushing in will keep that door open, making it a poor way to stop th water. Apr 26, 2023 at 17:39
  1. Do not load the most recent active save;
  2. Load an older autosave that is prior to the flood;
  3. Be happy.
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    While I guess a solution to your problem, its not really an answer. You're not dealing with the flood by means of in-game mechanics, but instead just reverting back to before the accident.
    – Timmy Jim
    Apr 26, 2023 at 15:03
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    It was the solution I chose, after trying to deal with the flooding by following the other answers. That is, I gave up, because I could not stop the flooding quick enough. But you are right, and I will not accept my own answer as the correct answer to the question. Apr 26, 2023 at 15:18
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    I was originally going to include a tongue-in-cheek "option 2: Just give up" in my answer, but ultimately decided against it. I guess that was the real solution after all.
    – qazmlpok
    Apr 26, 2023 at 21:42
  • @qazmlpok The cave-in would be the best fix to the leak, but, since it was so near the world border, I could not do it. Apr 27, 2023 at 0:26

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