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Author Topic: Why did my flood gate get washed away??  (Read 3751 times)

daggaz

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Why did my flood gate get washed away??
« on: January 12, 2018, 06:16:27 am »

I am filling my castle moat with hot molten magma, which comes from a pipe that extends many z-levels above my fort and the layer of my moat.   I am of the understanding that, if I were to simply tap a channel straight into this pipe with no cut-off, then the magma will keep pouring out until it fills my moat and then overflow and destroy the world, no? Or is the lack-of-pressure thing enough to keep that from happening?

Regardless, in the interests of !safety! I decided to put in an extensive cut-off system, all of it made from gabbro or alunite, including the mechanisms.  I built a raising draw bridge raising up towards the pipe, and raised it.  In the space next to it, I built a wall-grate.  In the next square, I built a flood gate.  I then built a second draw-bridge raising up away from the pipe.  Now once my system is full of magma, I can raise both bridges and make the gate-system impervious to building destroyers. 

But it didn't work that way..  I dropped the bridges and opened the grate and the floodgate, and used the busy-to-leave method to mine out the last square, opening the pipe.  My legendary miner high-tailed it out of there, and the magma was hot on his trail.

But it SWEPT THE FLOODGATE AWAY!!!  There is a gabbro floodgate with an alunite mechanism making its way down my chamber.  Is this fort lost?  Can I ever seal the chamber again?  Especially in light that draw-bridges are not supposed to block fluid for much longer (if they still do).

WHY did the magma sweep away my flood-gate??  For Armok!  >:(

I will add that I cleared the chamber of stones first... 

« Last Edit: January 12, 2018, 06:19:00 am by daggaz »
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PatrikLundell

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Re: Why did my flood gate get washed away??
« Reply #1 on: January 12, 2018, 07:36:37 am »

Unless you use screw pumps magma isn't pressurized, so magma flowing out of the middle of a magma pipe will not reach above the breach (but still flood everything lower that can be reached by normal flow from that breach, unless it evaporates). Thus, your world is safe (and everything flowing off an embark just disappears anyway).

Drawbridges block fluid indefinitely when raised. If they're not made completely of magma safe material they'll get destroyed while lowered, and a magma safe bridge with a magma unsafe mechanism is said to get destroyed if the mechanism is exposed to magma, which I understand to mean the bridges' lengths is either 2+ or 3+ (not sure if 1.5 counts as safe or not).

I have no idea about the floodgate question, though, as I use bridges exclusively. The obvious guess is that the flood gate was just dropped there, rather than actually built there, or possibly that the building was broken off partway through so it was half built.

You can plug the breach relatively easily by obsidianizing it with water either dropped from two Z levels above or flowing from the level above or beside (this case is probably not relevant, as most cases would have the tile beside being obsidianized instead).
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daggaz

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Re: Why did my flood gate get washed away??
« Reply #2 on: January 12, 2018, 08:34:57 am »

Ok, thanks.  But yeah, I definitely had built the floodgate (and used a lever to open it). 
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daggaz

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Re: Why did my flood gate get washed away??
« Reply #3 on: January 12, 2018, 10:18:35 am »

Just did it again, this time with a grate (set to open so you could wak thru the space).  Im just not gonna bother with these items if the magma is going to keep knocking them to pieces.   Drawbridge exploit all the way. 
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Loci

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Re: Why did my flood gate get washed away??
« Reply #4 on: January 12, 2018, 02:01:29 pm »

WHY did the magma sweep away my flood-gate??

Note that *any* non-magma-safe mechanism attached to a magma-safe floodgate will cause deconstruction when the mechanism is destroyed. You can view a list of all the mechanisms attached to a building using 't'. The only way to remove an attached mechanism is to remove the building and then rebuild it.
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daggaz

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Re: Why did my flood gate get washed away??
« Reply #5 on: January 12, 2018, 04:04:27 pm »

Sorry, but please note that i used magma-safe materials for the mechanisms as well as the flood-gates (unless the wiki is wrong?). 
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martinuzz

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Re: Why did my flood gate get washed away??
« Reply #6 on: January 13, 2018, 04:25:23 pm »

The wiki could be wrong, at some point during the updates the melting temperatures were redone to be more accurate.

Your safest bet to look up magma-safe stones is in game. Stocks >> stone screen.

EDIT: checked ingame, both gabbro and alunite should be magma safe, so no wiki error there.

No idea why your things got desconstructed. Perhaps a building destroyer magma creature made it's way to it? That, or you have found a bug.
« Last Edit: January 13, 2018, 04:31:35 pm by martinuzz »
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daggaz

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Re: Why did my flood gate get washed away??
« Reply #7 on: January 14, 2018, 02:38:33 am »

I found an old reddit thread on google, that suggests the problem occurs because a single loose stone (formed from digging out the last tile) is pushed by the magma into the floodgate and the !physics! destroys (deconstructs) the floodgate and its mechanism, even tho the floodgate is open. 

I think this is supported by the fact that I went back to my earlier save and removed the floodgate manually, then pierced the magma chamber, and that time it was the wallgrate (which was also opened and also of the same material) which got deconstructed.  Not sure tho why the grate didnt get wrecked the first time, it came first in line towards the magma, but maybe i just didnt see it in the depth of the flow. 

I would say its a bug tho, or at least bad design, if boulders pushed by magma can destroy open gates.   It just incurs a lot of unnecessary tedium as you would need to pierce the chamber, shut off the flow with a bridge that isnt affected by the problem, let the magma evaporate, remove any stone if it formed, then install the floodgates and grates further downstream before opening it all up again. 

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Quietust

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Re: Why did my flood gate get washed away??
« Reply #8 on: January 14, 2018, 09:02:27 am »

If you upload a copy of your save to DFFD, someone here could analyze it and figure out exactly why your floodgate and/or wall grate mysteriously deconstructed itself.
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P.S. If you don't get this note, let me know and I'll write you another.
It's amazing how dwarves can make a stack of bones completely waterproof and magmaproof.
It's amazing how they can make an entire floodgate out of the bones of 2 cats.

daggaz

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Re: Why did my flood gate get washed away??
« Reply #9 on: January 14, 2018, 09:08:43 am »

I already deleted it unfortunately :/

Easily reproducible tho if its not a super rare thing.  Dig a two-wide tunnel, leave the stones in.  Wall up one side of it (because I was dumb), then install a flood gate and a wall grate using those two materials, set them both into open position, and let the magma floooow.

For !science!.
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Larix

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Re: Why did my flood gate get washed away??
« Reply #10 on: January 14, 2018, 02:24:00 pm »

Grate and floodgate were not harmed or deconstructed (built of galena, with galena/sphalerite mechanisms). A dozen carefully-placed rhyolite and one obsidian got magma-washed through.

Reproduction failed; more detailed instructions required.

And i wouldn't trust random reddit threads any further than i could spit them; they tend to produce even more unfounded guesswork than bay12.

PS: i ran the basic floodgate function test, too: built it, opened it, dumped some junk in its square, ordered it closed. Floodgate gets stuck open and instantly closes without further lever-pulls required once the blockage is gone.
« Last Edit: January 14, 2018, 02:34:11 pm by Larix »
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daggaz

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Re: Why did my flood gate get washed away??
« Reply #11 on: January 14, 2018, 03:10:39 pm »

How close were they to the point of breach?  Mine were on the 3rd and 4th tile, respectively (first grate then floodgate).  Just saying because if its some kind of physics, the depth of the lava hitting the gates might change the force exerted. 

Also I used gabbro and alunite, but I suspect you changed those to see if you could get a possitive occurance using another magma-safe material. 
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Quietust

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Re: Why did my flood gate get washed away??
« Reply #12 on: January 14, 2018, 03:21:58 pm »

How close were they to the point of breach?  Mine were on the 3rd and 4th tile, respectively (first grate then floodgate).  Just saying because if its some kind of physics, the depth of the lava hitting the gates might change the force exerted.

I'm fairly certain that there are no "special physics" of that sort in the game.

Also I used gabbro and alunite, but I suspect you changed those to see if you could get a possitive occurance using another magma-safe material.
Larix probably used different magma-safe materials because they were the only ones conveniently available - without access to your fortress where the problem happened, it's the only reasonable option.

You say that you used magma-safe mechanisms in both the floodgate and the wall grate. Are you 100% certain that those were the only mechanisms in there? Not too long ago, somebody else reported a bug where drawbridges were melting even though they used magma-safe mechanisms, and it turned out that they had also been linked with non-magma-safe mechanisms to levers that were subsequently deconstructed, leaving the unsafe mechanisms still inside the bridge (where magma could melt them and cause the bridge to deconstruct).

Extraordinary claims require extraordinary evidence - unless you can provide that evidence in the form of a save file demonstrating the problem, all we can do is assume that you did something wrong (which is very frequently the case for Dwarf Fortress players).
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P.S. If you don't get this note, let me know and I'll write you another.
It's amazing how dwarves can make a stack of bones completely waterproof and magmaproof.
It's amazing how they can make an entire floodgate out of the bones of 2 cats.

daggaz

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Re: Why did my flood gate get washed away??
« Reply #13 on: January 14, 2018, 03:41:59 pm »

Positive I only used one mechanism on each building. Confirmed by finding only one mechanism and one building in each instance of breakdown. Positive both buildings were installed correctly, given that they are built in the closed position and I had to open them with the levers in order to access the magma tile.

I'll have a look later in my deleted files and see if I can't find it.
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Quietust

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Re: Why did my flood gate get washed away??
« Reply #14 on: January 14, 2018, 03:51:58 pm »

Positive I only used one mechanism on each building. Confirmed by finding only one mechanism and one building in each instance of breakdown.
That isn't necessarily definitive - if there was a second unsafe mechanism in the building, it would've turned into a "magma" item when it melted (showing up on the map as even with SHOW_FLOW_AMOUNTS turned on), which you could have easily overlooked.
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P.S. If you don't get this note, let me know and I'll write you another.
It's amazing how dwarves can make a stack of bones completely waterproof and magmaproof.
It's amazing how they can make an entire floodgate out of the bones of 2 cats.
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