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[HraTaika]

So, I'm building my drowning chambers and I'm little uncertain on the draining design. Basically, I'm going to run the water from a river to the chambers throught a couple of floodgates and a fortification. Now the drainage is harder.

Apparently, stuff and bodies will float through the fortifications, so I need to figure a mechanism which is building destroyer safe, but which can be 'maintained' easily (haul the goblinite) while still draining the water the from th chambers.

Thus, my first idea is to drain the water through a couple of fortifications on the same z-level as the chamber floor, behind which there is a pit and a hatch cover leading to a tunnel that drains to the egde of the map. This however, doesn't fit with the fortress layout as I would need to deconstruct the fortification in order to get to the loot.

The second idea is to have a pit behind the fortifications leading to the said tunnel. However this tunnel wouldn't run all the way to the edge, but rather, it would be positioned according to the fortress layout leading to the 'collection chamber'. It would have a pit and a hatch cover in the middle (to which the goblinite would get stuck yes? also when it's closed?) and a floodgate connection to maintenance corridor leading to the main fort. The water would drain yet another z-level downwards throught the hatch and along another tunnel to the edge of the map.

.. thus my question is, does this plan have any particular loopholes in it?

[Urist McSpike]

Water drains a lot slower than you want it to.    There are three things to pay attention to - your "goblin catchment" area, getting the water in, and getting the water out.  There are three design challenges - trapping a large number of invaders, flooding the area quickly, and draining it quickly.

For example, my current fort has this setup.  My water reservoir is a 4 z level pit that is about 15x15 on the bottom level, with ramps at the edges & expanding outward as it goes up.  The bottom is next to my Drowning Chamber, and lined with floodgates & fortifications.  Then, the entry hallway/drowning chamber is floored with retracting bridges (five 3x10, which I'm currently expanding).  The floor below the bridges is channeled out, to a "collection area", which is equal in size to the drowning chamber area, with many channels covered by grates.  Then below that, I have a draining area which floods a large chamber, to dissipate water & allow underground tree farming.

The big thing to understand is how quickly water will fill or drain from an area - a few drain spots will take a long time to do it, which can be very bad if it's your only entrance.  If you get a large head of water, the pressure will cause it to flood faster, and a large drain area will drain it faster.

Off to work now, but I might try to post some pics later today, if you want.

[HraTaika]

Off to work now, but I might try to post some pics later today, if you want.

Pictures would be very much appreciated!

[Thorus]

From what i've read and imagine:

Side view:

Code: [Select]

#~~~~~~~~~~~~~~~~~~~#
###~~~~~~~~~~~~~~~###
#####~~~~~~~~~~~#####
#######~~~~~~~#######
#########hhh#########
#######.F...F.#######
#######.#####.######
...b.............b..
####bbbbbbbbbbbbb####
####.............####
####.............####
####.............####
####.............[outflow / pumps / cleaning]
#####################

# = wall / stone
b = bridge
~ = water
. = open space
h = hatch cover, linked to a lever
F = fortification

1) let goblins in
2) close both bridges on the floor
3) open hatches
4) water will pour down through the fortifications and drown the gobbos
5) wait till all gobbos are dead
6) close hatches
7) open bridge to drop water + gobbo remains into the draining chamber
clean draining champer (pumping the water to the reservoir, edge of map, aquifer, caverns, dining hall, ...)

[Urist McSpike]

Lets see if I can do this right.   

The water reservoir (shown in the first pic) is the base of a 4 z-height pit.  The bottom level is 15x15, rising to 17x17, 19x19, and 21x21 at the top.  This (plus a few incidental spots) allow 1360 spaces of water, for a total of 9560 units of water.  The water pressure from this instantly floods the drowning pit, when the floodgates are opened.  It also provides plenty of water for the wells, in case of emergencies.

Spoiler: The drowning chamber (click to show/hide)

Z 0
The top left passage leads off to the wells.  All floodgates are linked to a single lever, to flood the hallway.  All five of the 3x10 (retracting) bridges are linked to a single lever, for draining.  And most important, the 3x3 bridges raise to block off the actual drowning chamber.

Spoiler: The loot room (click to show/hide)

Z -1
Bodies & other goodies are left here, for fast and safe recovery.  Be sure bridge is raised before draining the chamber above.  Lots of grates to quickly drain water into the area below.

Spoiler: The drainage area (click to show/hide)

Z -2
The ramps on the right are directly below the grates in the chamber above.  Area was calculated to allow a full load of water from the drowning chamber to spread out with a maximum 2 depth, allowing evaporation.  The flooding will also allow the growth of underground plants & trees.

Edit: Horrible sizing on Fixed the images, here is the imgur album for better viewing.

[TheBlueSteel]

Personally I've always found wall and water traps to work best when combined.

I usually make a entrance area that is a retractable drawbridge(s), then have a 5-10z level drop underneath that into the 'drowning chamber'. Once any goblins fall down they are stunned/injured, at which point I either let in my military to kill the severely wounded cretins or flood the chamber. This chamber's floor is also composed of retractable bridges, and so once everything is dead I retract said bridges again onto a layer of floor grates that feed into the caverns/a pump system to return the water to its river home.

Easy peasy, all the gobbos die and I get their loot.

[gchristopher]

I prefer bridges to atom-smash the water in the drainage area if I don't have an aquifer to absorb the water. (Also, any square at lake level will absorb water dropped from above, if you're near a lake.)

With a little planning, you can put a water-activated pressure plate in the draining area to control the water smashing bridge and it'll be fully automated with unlimited draining capacity.

[Urist McSpike]

I prefer bridges to atom-smash the water in the drainage area if I don't have an aquifer to absorb the water.

While there are plenty of ways to dispose of water, I decided to get double usage with a tree-farming area.  As long as you calculate the amount of water versus the floodable area and make sure that you close all required areas before flooding, it's easy enough to do.

In the first image, you can see my planned expansion.  As it is now, I'm limited (by pathing) on how many enemies I can trap inside - I plan on extending it around into the designated lopsided U shape, to give me a bigger area to catch enemies.  The top passage going to the right is my short-cut, for worker passage - since I have a batch of traps in it, caravan wagons are forced to go the long way around.

I think the biggest problem to this type of trap design is underestimating water flow.  The number of openings isn't really the issue - it's how much water pressure is going to act on those openings.  If you have one level of water spilling in, it will take a lot of time, but if you have multiple z-levels of water, it will flood a lot faster.  Likewise, draining can take time, even if you use pumps.  It's faster to use large area bridges over a catchment area, and then drain/pump out of that.

Also, a very important note - you have to do any landscaping before building your bridges, whether you want to construct floors or channel out under the bridge area.  Once you build the bridge, you can't raise it & do the work.  (At least it used to be that way, unless something has changed.)

[Dorf3000]

I used to be a drowning chamber builder like you, but then I took an arrow to the knee...

My advice on drowning chambers: always use at least a 2z level reservoir or have the source at least 2z above the chamber, so you can fully use the water-teleporting effect as the game simulates pressure.  If you have the water flowing in sideways it'll take a long time to fill, but if it can pass through full 7/7 blocks of water and drops at least one z level, it will teleport there instead of flowing.  The most common design I used had the water come down a very shallow u-bend and up through the floor of the chamber, it fills extremely quickly.

When draining, the collection floor should be made from grates if possible - otherwise water has to flow sideways off the floor, pushing your loot and potentially water-breathing enemies into places they shouldn't go.  It's also a good idea to build nasty bladed traps in the access corridor just in case something is able to survive your watery welcome - this happens more often than you would like, especially on the first test run when you find out something didn't quite go as planned.

Lastly, if you find that your original trap wasn't... impressive enough to hold all the eager little goblin children who want to ride in it, build your extension in parallel to it if you can, rather than lengthen the original - you never know when another schoolbus full of stinky little devils will appear and demand to be let in, and it's good to have at least some way of entertaining them for the rest of their extremely short lives.

[terko]

Easiest way to drain water: pump it into an aquifer.

[Urist McSpike]

I usually make a entrance area that is a retractable drawbridge(s), then have a 5-10z level drop underneath that into the 'drowning chamber'. Once any goblins fall down they are stunned/injured, at which point I either let in my military to kill the severely wounded cretins or flood the chamber.

I was working on a design in one fort that captured my imagination (abandoned due to upgrading, I think).  I had a large (10x20) 3 level high underground "courtyard", which was going to be a drowning trap.  Right alongside it, on the middle z-level, was going to be my grand Dining Hall/Meeting Room - with a glass wall.  I imagined my dwarves eating, drinking & just hanging out, while laughing at the antics of the drowning goblins.   Yes, I know - glass block walls do not equal windows.  But it was still an amusing thought.  (Mommy, mommy!  Look at the mer-goblin!)

Do critters drown when there is open space above the 7/7 water?  Or do they swim along, bobbing up for air?  For some reason, I thought they need a roof to keep them trapped underwater.

[Logen910]

you forgot magma. and deadly carp. aybe a drain directly into hell would be a good idea. I am not joking about this. For me it was always a source of great fun and laughter.

[Triaxx2]

Few things could be as fun as draining carp into hell and watching them tear apart the locals.

I have two suggestions. One is to not make it bigger than 20x20. Build the bottom out of retracting bridges, and the roof out of the same. Fill the area above the chamber with water, and set it up so a gobbo stepping on a pressure plate slams the entrances (I combine hatches and flood gates for both speed and the fact that while FG's have a time delay, hatches don't.

One level beneath the lower bridges the floor consists of alternating bands of grates and floors, constructed or natural. Underneath is a storage chamber with pumps to reload the water. I connect the pressure plate to a repeater to open the bridge, and close it again. That way they don't float out the top while I'm waiting for them to get dead.

[ResMar]

http://dwarffortresswiki.org/index.php/DF2012:Drowning_chamber

[Quietust]

I made a "drowning entrance" in one of my 0.31 fortresses, and the way I handled drainage was to just [url=pump it out from above - as long as you pump the water out from the center of the room (or ideally from multiple points evenly distributed from the edges), the chamber should empty out quite rapidly.