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[Locksoli]

I'm a little new to DF in general, but I've gotten most things down so far except for complex projects like this. But I tweaked my rivers to have bull-sharks, and I want to make a drowning chamber to catch some for my meat industry. I have a little square spot channeled out, and I wanna know if I could feasibly make a drowning chamber out of it and use it to bag me some sharks, and how to do so.

image for reference

Spoiler (click to show/hide)

 

[KevinM]

I think it looks good so far. You'll want several more things though.
1:  a floodgate or bridge (usually a bridge), connected to a lever (where the lever is in the main base).  You'll probably want to create a corridor (without opening to the river yet) by channeling one square either in the top or the bottom left corner of your chamber, building the bridge or gate in that square, and close it to seal off water from getting in, then which after you finish linking and building the rest of the chamber, you can then channel the last square to the river.  This way it'll allow water and creatures in when you open the gate/bridge.   https://dwarffortresswiki.org/index.php/DF2014:Floodgate and https://dwarffortresswiki.org/index.php/DF2014:Bridge#Floodgates 

2: A way to get water out, usually a pumpstack powered by a waterwheel or windmill, also with a gear connected to a lever to turn it on and off.  I usually have mine going off the map after some mishaps where the excess caused some dwarves to go into the river and drown.  I'd consider creating an aqueduct to a walled off chamber that opens above the river but I'm not entirely sure how the water pressure works and what issues it can cause.  I did it once but my fort stress died.
3:  cage traps if you want to trap the sharks/fish

[Quarque]

You need:

1. A channel to let the water in, which can be sealed off.
Build the `sealing off part´ first. It can be a raising bridge connected to a lever, or a floodgate connected to a lever, or even a door connected to a lever. The raising bridge is safest and easiest. Build any type of seal and close it.
Then dig out walls to let the water stream unto your closed seal. The safest option is to channel them out from above. Careful if you channel out multiple tiles. Do them in the correct order. If a dwarf is able to get stuck or drown, he will.

2. Now build a screwpump to pump the chamber dry. The wiki has good detailed instructions on how they need to be build and how they work. Basically, you pump from a hole above your chamber and back into the river. Be sure the water you pump out can only move back into the river, not into your fortress.

[Locksoli]

You need:

1. A channel to let the water in, which can be sealed off.
Build the `sealing off part´ first. It can be a raising bridge connected to a lever, or a floodgate connected to a lever, or even a door connected to a lever. The raising bridge is safest and easiest. Build any type of seal and close it.
Then dig out walls to let the water stream unto your closed seal. The safest option is to channel them out from above. Careful if you channel out multiple tiles. Do them in the correct order. If a dwarf is able to get stuck or drown, he will.

2. Now build a screwpump to pump the chamber dry. The wiki has good detailed instructions on how they need to be build and how they work. Basically, you pump from a hole above your chamber and back into the river. Be sure the water you pump out can only move back into the river, not into your fortress.

I think it looks good so far. You'll want several more things though.
1:  a floodgate or bridge (usually a bridge), connected to a lever (where the lever is in the main base).  You'll probably want to create a corridor (without opening to the river yet) by channeling one square either in the top or the bottom left corner of your chamber, building the bridge or gate in that square, and close it to seal off water from getting in, then which after you finish linking and building the rest of the chamber, you can then channel the last square to the river.  This way it'll allow water and creatures in when you open the gate/bridge.   https://dwarffortresswiki.org/index.php/DF2014:Floodgate and https://dwarffortresswiki.org/index.php/DF2014:Bridge#Floodgates 

2: A way to get water out, usually a pumpstack powered by a waterwheel or windmill, also with a gear connected to a lever to turn it on and off.  I usually have mine going off the map after some mishaps where the excess caused some dwarves to go into the river and drown.  I'd consider creating an aqueduct to a walled off chamber that opens above the river but I'm not entirely sure how the water pressure works and what issues it can cause.  I did it once but my fort stress died.
3:  cage traps if you want to trap the sharks/fish

Alright, what I have so far is this

the above area isn't undergound, it's actually on the surface.

Spoiler (click to show/hide)

 

So my plan is to build a screw pump on that surface z-level, just where the blue line in the pic below is marked, in hopes that I'll be able to use it to pump water out.

Spoiler (click to show/hide)

 

the plan is that I'll be able to attach a lever to the door below so I can open and close it, and I'll have the entire floor covered in animal traps for anything that swims in.

[KevinM]

Just for clarification, You'll want cage traps, and not animal traps, since animal traps are only for vermin.   Though I think just not having any traps and making dwarves go fight could work too.

I really don't recall the water pressure thing on rivers, so someone should mention how that goes.  I think it still creates a water level above the river surface which can wind up sweeping things in or getting mud in the surrounding surfaces, so walling off next to the pump may help.  I just can't accurately recall.  But if you're using a waterwheel and gear with a lever to power/unpower the pump, you won't have to worry about your pumpdwarf drowning.

[Locksoli]

Just for clarification, You'll want cage traps, and not animal traps, since animal traps are only for vermin.   Though I think just not having any traps and making dwarves go fight could work too.

I really don't recall the water pressure thing on rivers, so someone should mention how that goes.  I think it still creates a water level above the river surface which can wind up sweeping things in or getting mud in the surrounding surfaces, so walling off next to the pump may help.  I just can't accurately recall.  But if you're using a waterwheel and gear with a lever to power/unpower the pump, you won't have to worry about your pumpdwarf drowning.

The animals I want to nab are fully aquatic, so they'll air drown the moment I've pumped the water out. I don't plan on powering the pump with a water wheel/windmill, so I'll just have a pump operator handle it, but I'm hoping that it wont cause problems.

[anewaname]

I agree with what KevinM says about the risk of water from the pump sweeping things into the river. Dwarfs drown when the outflow from the pump reaches the tile where the pump dwarf stands.

[mightymushroom]

the plan is that I'll be able to attach a lever to the door below so I can open and close it, and I'll have the entire floor covered in animal traps for anything that swims in.

The animals I want to nab are fully aquatic, so they'll air drown the moment I've pumped the water out.

Never tried personally but word is that they will NOT air drown if you have them in cage traps before pumping – imagine that when the cage is used underwater it shuts tight and keeps the water inside. (Breathing status is 'locked' to whatever it was when the creature entered the cage.) If that's what you want, cool. Bonus points if you now make a glass-floored throne room with live sharks swimming underneath.


RE: wall
For performance reasons, liquids do not check for gravity as often as in real life. Pumped water is likely to spread a surprising distance horizontally, including backwards into the pit and/or operator's station if there is no safety barrier. Once gravity does happen the water should fall into the river and disappear off the river's downstream edge, and is unlikely to cause other problems from this kind of temporary pumping unless you have something else that connects to the river and suddenly gets excess water.

[Quarque]

To make it more clear, here is the basic idea of how you can use walls (and floors) for safety as suggested:

~~#....
~~#....
~~÷÷×..
~~#....
~~#....

~ = river (1 z level below)
÷÷ = screwpump pumping from east to west
# = walls to protect pump operator from outflow
. = drowning chamber, covered by floor
x = floor hatch

The pump can suck water up through a floor hatch as in the picture, to protect dwarves from fishes in the chamber before they drown.

[Locksoli]

So, I have the prototype set up

Spoiler (click to show/hide)

 

As you can see, it's currently crude in design and lacks quite a few safety measures mentioned, but installing a floor hatch shouldn't be an issue in the near future. So far, I know it works, but the dwarf I designated for pump operating is not trained and has easily exhausted himself in his endeavors.

For context, the "miner" in the hole is actually my king. In all my previous worlds (read: Me constantly regenerating the same world if I suddenly experiences an overabundance of bugs) my rulers were female, so I was wary of having a male ruler as I was not familiar with kings in general. But he proved himself to be of good use to our fledgling fort, and many a dwarf had their morale boosted by the presence of their ruler...right until he mandated the crafting of "Pond Turtle Leather boots".

I decided then and there that perhaps his lack of knowledge might leave him prone to an...accident?

[Quarque]

yikes, I was sleepy when I posted that reply. I meant to say a floor grate, not a hatch. Sorry.

The safety measures may not be strictly needed in this case, but once you know them, you can build a magma chamber too (of course you need magma-safe materials then).

The left tile of the pump acts like a wall, impassable to dwarves and fluids. The right tile can be passed by both.

Sounds like the king dug his own grave. :p

[PatrikLundell]

Did the king actually issue such a mandate, or was it actually a demand?

The former results in the harming/death of a random dorf when not met if the injustice system is active, while the only result of failing to meet an (impossible) demand is a grumpy monarch.
Impossible demands are not uncommon (in particular non wooden beds), while I haven't heard of mandates specifying exact materials (Leather Boots, yes, but not the specific type of [non existent] leather).

[Locksoli]

Did the king actually issue such a mandate, or was it actually a demand?

The former results in the harming/death of a random dorf when not met if the injustice system is active, while the only result of failing to meet an (impossible) demand is a grumpy monarch.
Impossible demands are not uncommon (in particular non wooden beds), while I haven't heard of mandates specifying exact materials (Leather Boots, yes, but not the specific type of [non existent] leather).

It was a demand if I'm remembering it, but the stuff he mandated as well isn't really useful either (He ordered the construction of fuel of all things) but since I don't have a justice system in place, I'm not worried just yet. So I tried the drowning chamber on him...and my test was a moot point, since he's a competent swimmer. I checked him, and it turns out he has a reason to be pretty stubborn: he doesn't have any heirs whatsoever. I'll just have to keep him around and ignore his useless demands until he has kids to replace him.

Still, my shark killing chamber works. I might add a bridge if I ever need to get rid of some goblins or any agents if they decide to come after my future artifacts.

[PatrikLundell]

It doesn't matter if a monarch has an heir or not. You'll most likely get a new randomly selected dorf in the fortress as a replacement. In theory you could kill them off until you happen to get one who's not a mandate spewer, but expect to lose maybe 20 dorfs in the process (and probably a number of those you don't really want to lose).

[KevinM]

Did your pump work? I can't tell but I don't think you have a ramp on the inlet which is needed to draw water into the pump.