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[darkrider2]

This is the kind of trap that is built as the entrance to your fort. The idea is to have a hallway that will fill up with water from the bottom instead of the side or top, but most of all it utilizes water pressure.

So build a three wide hallway with grate flooring and put raise-able bridges on each end to trap invaders. Build a cystern under the hallway and build a water tower (higher z-level) somewhere nearby.

Build a tunnel from the water tower to the cystern so it drains into it, place floodgates diagonally inside it, and connect them to a lever. Build a pump stack on the floor above the hallway that pumps water from the hallway to the water tower.

When the floodgates are on, the water pressure will not travel from the water tower to the cystern. when you pull the lever however, the water should begin to rise out of cystern via water pressure, flooding the hallway.

To drain and reset. Reactivate the floodgates, and turn on the pump stack. Just make sure the pumps aren't running while your flooding the hallway or it will keep it from fully flooding to 7/7.

I'm so using this in the DFM3 competition.

[Hyndis]

Yup.

If you embark in a freezing climate, like on a glacier or tundra, you can use this for a cryo-trap.

The water rises from below due to water pressure, and as soon as it reaches above ground it freezes solid, instagibbing everything trapped within the ice.

Once everything is dead send in your miners to dig out the ice and then collect the goblinite.

You can use pumps on either side of a corridor, though you're limited to having a 2 tile wide corridor if you do that approach, and you are vulnerable to building destroyers. They can just smash your pumps.

You could also use stairs. On the level open to the sky and the freezing weather, all of the ground will be down stairs.

On the level below will be water, subterranean so it will not freeze, and up stairs.

To trigger the trap open up the floodgates from your reservoir to use water pressure to force the water up from the lower, liquid level to the open, freezing level. As soon as even 1/7 water hits the cold air it will freeze solid, killing everything within that tile.

Cleanup is easy. The ice will stop further water from flowing, meaning that the trap would actually use very tiny amounts of water each time its triggered. Just close the floodgates to remove the water pressure and dig out the ice.

[Trigonous]

And with the frozen water method, you would pump water into the tower from a separate source (as any water pumped into the trap is now useless as water) so no machinery is exposed to invaders.

[Hishan]

An excellent trap idea, water pressure is underused.

Also (correct me if im wrong) but I dont believe that that ice trap would work, as the water rose from beneath it would already be flagged as OUTSIDE beacause you removed the floor to build a grate, and so would freeze in your tunnels. Pumping it in from the side would work however (im fairly sure theres a video of that somewhere).

[lastofthelight]

DF water pressure gives me physicist headaches, I've never understood it.


1. What is the purpose of the diagonal floodgates?
2. Why is water rising out of the cistern?

The way I would imagine this if this were real, would be I would have water from the tower push the water in the cistern up through the floor, but I'm not sure if DF works that way.

[EliDupree]

The thread title gave me a delicious idea. Put dwarven water elevators next to your entrance. Station half of your army near the main entrance and half of them in the elevators. When the enemies have entered, turn on the elevator and attack from both in front and behind! This could also be used to catch fleeing thieves, although it's an absurdly elaborate way of doing so.

[darkrider2]

water pressure is underused.

agreed. and no... if you build the grates first the tiles below will be inside and shouldn't freeze.

[Caesar]

The thread title gave me a delicious idea. Put dwarven water elevators next to your entrance. Station half of your army near the main entrance and half of them in the elevators. When the enemies have entered, turn on the elevator and attack from both in front and behind! This could also be used to catch fleeing thieves, although it's an absurdly elaborate way of doing so.

*Ping!*

'And so the bloodthirsty dwarves screamed and shouted, supported on the background by excruciatingly boring elevator music, as they charged the kobold thief, whom had been caught by surprise so great that he turned green.'

                                                                -- The story of how goblins were born. -- Telling 1

[Hishan]

water pressure is underused.

agreed. and no... if you build the grates first the tiles below will be inside and shouldn't freeze.

Ah I see, so build the grates, the dig ramps underneath to collapse the floor? I wonder if that still flags as inside or not, Im going to run a quick test

EDIT: This in fact does not work (unless im using the wrong stategy), ramping beneath the grate still causes a floor under the grate, and the grate itself cannot be channelled to allow water though.

[Caesar]

Perhaps you should first dig out the hallway (have it be underground), then dig the channels and place your grates and only then channel out the top floor to make your hallway outside.

[Hishan]

Perhaps you should first dig out the hallway (have it be underground), then dig the channels and place your grates and only then channel out the top floor to make your hallway outside.

Myth confirmed, by channelling everything, and building your grates completely underground then removing the top layer to expose it to the outside the tiles under the grates are INSIDE, and the grates are in open space. The cyro trap will work, well done sir!

This does however pose one problem, will building destroyers attack grates? If so they could irrepreably damage your trap by exposing your under-grate tiles to the outside.

[Kagus]

"Inside" doesn't change whether or not water will freeze.  "Subterranean", on the other hand, will.  And as soon as you remove the natural rock from above a tile, it becomes "Above Ground" and can never be reset. 

You can, however, send magma underneath a water chamber in order to keep it liquid.  The use of this is debatable however, as the small amounts of water that would flow through the grates would  instantly freeze before they can gain any real depth (and possibly blocking off the flow).

An alternative is to just fill a heated above-ground chamber with water and then remove the magma.  As the heat sources disappears, the water should freeze.  This can be especially interesting as (according to the wiki) even a layer of 2/7 water will freeze into a wall (thus killing anything in the tile).  This makes it possible to keep a constant "footbath" of low-level heated water in an area so that invaders can path through it on their own.  Then it's just a matter of dropping the magma.

[Hishan]

"Inside" doesn't change whether or not water will freeze.  "Subterranean", on the other hand, will.  And as soon as you remove the natural rock from above a tile, it becomes "Above Ground" and can never be reset. 

You can, however, send magma underneath a water chamber in order to keep it liquid.  The use of this is debatable however, as the small amounts of water that would flow through the grates would  instantly freeze before they can gain any real depth (and possibly blocking off the flow).

An alternative is to just fill a heated above-ground chamber with water and then remove the magma.  As the heat sources disappears, the water should freeze.  This can be especially interesting as (according to the wiki) even a layer of 2/7 water will freeze into a wall (thus killing anything in the tile).  This makes it possible to keep a constant "footbath" of low-level heated water in an area so that invaders can path through it on their own.  Then it's just a matter of dropping the magma.

You are correct, I ran another few tests and as the grates DO NOT conserve the subterranean tag they cannot be used. But the trap can still work, as long as you heat the bottom of the grated tiles with magma (i.e. have a layer of magma in a lake around your trap), they will stay as water I believe, so that even though they are ABOVE_GROUND they will not freeze, until they are pumped outside that is.

EDIT: im actually going to build this to see if it works, more updates later

[Hyndis]

An excellent trap idea, water pressure is underused.

Also (correct me if im wrong) but I dont believe that that ice trap would work, as the water rose from beneath it would already be flagged as OUTSIDE beacause you removed the floor to build a grate, and so would freeze in your tunnels. Pumping it in from the side would work however (im fairly sure theres a video of that somewhere).

Thats why I suggested up/down stairs.

You can carve stairs which will keep the area below subterranean, which means the water will remain liquid. Above the stairs is above ground where it will instantly freeze.


It also may be possible to do the exact same sort of trap, only with magma. I haven't tried it personally, but IIRC, it is possible to pressurize magma by moving it through a pump. I haven't verified this though, but thats what the rumor is.

If magma would work, you would instantly cook the entire siege using the exact same trap setup, and it would have the side effect of clearing away all of the junk, leaving only precious bones and goblinite left.

[Hyndis]

This does however pose one problem, will building destroyers attack grates? If so they could irrepreably damage your trap by exposing your under-grate tiles to the outside.

Yes. Even retracted grates will be targeted and destroyed by building destroyers.