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[lionrt60]

Well, I've just got to the point in the game where i'd want to drain a river/aquifer for a well and for general purposes, thing is I have no idea what-so-ever on how to do it without drowning dwarves or flooding my fortress :/ Please help! lol

[Em3rgency]

Floodgates! You dig out wherever you will want the water to be, and ALMOST link it to your water source. Make a way to drain the water, most commonly with a screw pump (or pumps if you need to go up several levels). Then you build all the floodgates where you will need them. That would be where your water would soon come from. Link the floodgates to a lever, test it if it works, build walls to close any connections to your fort and finally mine out the remaining bits connecting your reservoir to the river/lake/ocean and watch the water flow. Close the floodgates when its full or half full or whatever and test out your draining system if you bothered to make one.

Tl;dr;
Floodgates.

[Xinael]

To get you started faster, you can even use doors to hold back water. Just dig some tunnels, use doors to hold the water where you want it, and then mine the last bit out (channeling from above is usually safest for the miner - do the last tile from the surface, at the bank of the river, if it's a river you're using) and the water should go where you want. If not, try again - using dfhack's quicksave command is helpful for this kind of experiment, or doing your experimenting away from your fortress until you know what you're doing. The only thing that might catch you out is water pressure, which will make water go upwards in some situations. You can make the water pass through a diagonal gap to remove the pressure.

The walls are important for safety in permanent structures rather than playing around, though - creatures that are building destroyers will happily knock down floodgates and doors in their quest to enter your fort, and if they can swim the water is no obstacle. Not only will you have nasty monsters in your fort, but a massive flood as well.

[wierd]

A fortification slit or two will allow liquids through, but block most larger creatures.

Notable exceptions are things like magma crabs, carp, and the like. They go right through the slit.

A few of these constructed in the sluceway will help to filter out swimming invaders in some circumstances, but isn't a magic bullet. It should be enough to keep building destroyers off the floodgates, however, if done right.

[Xinael]

A fortification slit or two will allow liquids through, but block most larger creatures.

Notable exceptions are things like magma crabs, carp, and the like. They go right through the slit.

This is actually a bug - once the fortification has 7/7 water on it, any creature can path right through. Pretty much renders fortifications useless for liquid purposes. Definitely up there as one of the most annoying bugs for me.

[jez9999]

To get you started faster, you can even use doors to hold back water. Just dig some tunnels, use doors to hold the water where you want it, and then mine the last bit out (channeling from above is usually safest for the miner - do the last tile from the surface, at the bank of the river, if it's a river you're using)

Isn't that a bit of an understatement?  If you mine the last wall out instead of channelling, the miner would get swept away?

[Starver]

Isn't that a bit of an understatement?  If you mine the last wall out instead of channelling, the miner would get swept away?

Not long ago I made a post (here) which demonstrated using a zig-zag (later expanded to be a wider channel) behind a floodgate to mitigate water-flow that in this case was introduced by the fortification method, but could equally well have been by mining.

This other post dealt with channelling from above, which of course is much simpler, but not always possible. Or safe (e.g. from hostiles/nasty wildlife traipsing outside).

However, to expand, draining a river might best be done by setting up a whole lot of floodgates alongside a river (one still-undug tile between them and the water) with sufficient draining behind and then either mass connect the floodgates by channelling that remaining line of tiles out or (with individual lever-control on each floodgate) breaching each individually through a temporary zig-zag.  I could let you work out the logistics on how you do that...

Spoiler: ...but my suggestion is (click to show/hide)

(The following being plan view, not side-views, BTW...)

river/watersource
~~~~~~~~~~~~~~~~~
#################
##XXXXXXXXXXXX##
##.............##
##.............##
##.............##    <- prepared open area
##.............##

~~~~~~~~~~~~~~~~~
################# <- dig/fortify this tile
##XXXXXXXXXXXX### <- while opening this floodgate
##..........OO.##
##..........O.O##
##..........OO.##    <- some temporary walls for zig-zag pressure-reduction/escaping
##..........O.O##

Shift your zig-zags (note you can re-use some walls, in fact can not bother removing them until the end).

~~~~~~~~~~~~~~~~~
##############~## <- Then dig/fortify this tile
##XXXXXXXXXXXX### <- while just this floodgate open
##.........OO.O##
##.........O.OO##
##.........OO.O##    <- new temporary walls for zig-zags
##.........O.OO##

...eventually

~~~~~~~~~~~~~~~~~
####~~~~~~~~~~~## <- Final clearing
##XXXXXXXXXXXX### <- for the last floodgate that needs opening
##O.O..........##
##.OO..........##
##O.O..........##    <- new temporary walls for zig-zags
##.OO..........##

Then, when you're ready, get rid of all zig-zag remnants (which might well be filling almost the entire flood-cavern you've just created, if you wanted not to hold things up too much)...

~~~~~~~~~~~~~~~~~
###~~~~~~~~~~~~##
##XXXXXXXXXXXX### <- open them all
##~~~.~~~~~.~~~##
##~(whoosh!).~~##
##~.....~.....~##
##.............##

[Xinael]

Isn't that a bit of an understatement?  If you mine the last wall out instead of channelling, the miner would get swept away?

I meant that channeling isn't always an option depending on how dangerous your surroundings are and what water source you're using. Sometimes other options like Starver's method, using the dig-from-below bridge exploit, or building up-stairs where the miner will stand and praying he's fast enough end up being better. But yes, in most cases channelling is easiest and safest.

[jez9999]

Spoiler: ...but my suggestion is (click to show/hide)

(The following being plan view, not side-views, BTW...)

river/watersource
~~~~~~~~~~~~~~~~~
#################
##XXXXXXXXXXXX##
##.............##
##.............##
##.............##    <- prepared open area
##.............##

~~~~~~~~~~~~~~~~~
################# <- dig/fortify this tile
##XXXXXXXXXXXX### <- while opening this floodgate
##..........OO.##
##..........O.O##
##..........OO.##    <- some temporary walls for zig-zag pressure-reduction/escaping
##..........O.O##

Shift your zig-zags (note you can re-use some walls, in fact can not bother removing them until the end).

~~~~~~~~~~~~~~~~~
##############~## <- Then dig/fortify this tile
##XXXXXXXXXXXX### <- while just this floodgate open
##.........OO.O##
##.........O.OO##
##.........OO.O##    <- new temporary walls for zig-zags
##.........O.OO##

...eventually

~~~~~~~~~~~~~~~~~
####~~~~~~~~~~~## <- Final clearing
##XXXXXXXXXXXX### <- for the last floodgate that needs opening
##O.O..........##
##.OO..........##
##O.O..........##    <- new temporary walls for zig-zags
##.OO..........##

Then, when you're ready, get rid of all zig-zag remnants (which might well be filling almost the entire flood-cavern you've just created, if you wanted not to hold things up too much)...

~~~~~~~~~~~~~~~~~
###~~~~~~~~~~~~##
##XXXXXXXXXXXX### <- open them all
##~~~.~~~~~.~~~##
##~(whoosh!).~~##
##~.....~.....~##
##.............##

I don't understand why you'd do the zig-zag method (sorry if this is a dumb question).  Why not just do this:

~~~~~~~~~~~~~~~~~
################# <- dig/fortify this tile
##XXXXXXXXXXXXX## <- while opening this floodgate
##...whoosh....##
##...whoosh....##
##.............##
##.............##

[Starver]

1) More whoosh!. Without the zig-zag behind the digger/fortifier the water doesn't lose what little pressure it has and may well fill the void from any copious-enough water source (like a river) before the dwarf concerned gets around to escaping via the stairwell at the back.  (Actually, a couple of wall-contained diagonals should be enough, on top of the diagonals from the removed barrier to the floodgate and into the temporary section.  I went overboard.)

2) By letting the water through orthagonally to the floodgate you open (as opposed to diagonally to one side) you can't now open either adjacent floodgate without the water (albeit with the pressure taken away) leaking through the tile that you now want your digger to stand on to de-barrier the adjacent tile.

With the latter situation, especially, you probably wouldn't get anyone to stand on either adjacent floodgate's spot.  Which is why I started at one side and made it a matter of working diagonally away from the yet-to-be-dug barriers.  Close the open floodgate and open the one next to it and you still have 'safe ground', albeit through a route finally offset by one tile (not a big problem on anything wider than a single tile, and decreasingly so the longer it is until it doesn't matter much at all).

(Also, to add, that with floodgates you can set the floodgate control to "close" as soon as the dwarf concerned is working in that spot (or sooner, if the lever-puller isn't going to beat the floodgate-stander to his or her task position).  As soon as the job is complete and the dwarf moves back away from the floodgate[1] then the floodgate is free to close and very little liquid flows through.  I find this method useful when breaching magma (with magmaproof floodgate/etc, as appropriate!), for the obvious reasons, and can't remember the last time I had any problem with losing a fortification-carver.)






[1] Noting that I normally do this with fortification-carvers, so if for some reason the dwarf has an urge to walk through the gap he's just mined out, he's now trapped on the wrong side of the floodgate.  Probably not going to happen unless a pretty good swimmer encountering some strange momentary pathing anomolies, but I'll leave this in as a caveat so you can't say I didn't see it coming, if it ever does.

[jez9999]

2) By letting the water through orthagonally to the floodgate you open (as opposed to diagonally to one side) you can't now open either adjacent floodgate without the water (albeit with the pressure taken away) leaking through the tile that you now want your digger to stand on to de-barrier the adjacent tile.

You've really lost me here.  Sorry, I'm a newb.  Could you use a diagram to show what you mean about which tile you'd want your digger to stand on and why the water would leak through it?

[Starver]

water
##### <- dig here
XXXXX <- from this floodgate
.....
.....

...gives you...

water
##~##  <- that 'bank' tile is now a water-tile
XXXXX  <- assume you got the marked floodgate closed quickly enough
..~..  <- seepage (probably more than this), but will dry out
.....

Now if you want to dig from an adjacent floodgate

water
##~##  <- Want to clear this tile
XXXXX  <- so you open this floodgate
~~~..  <- but water immediately flows through open flood, diagonally, from the gap in the 'final wall'.
.~...  (In reality, there'd probably be enough water on the opened-floodgate tile to cancel your #-clearing job...)

water
##### <- but dig here
XXXXX <- from this floodgate (diagonally)
.....
.....

water
###~#
XXXXX
..~..  <- seepage (and probably far less, as well, due to the hydrodynamics of the diagonal), but will dry out
.....

water
###~#  <- But now this tile
XXXXX  <- can be reached by opening this floodgate
.....  <- Without any immediate water, because you've got three walls (until breached) between you and the watersource.
.....


Now obviously if you offset by one, you can only go one direction across the floodgates, hence starting at the side, and unzipping the bank/zipping back up the floodgates over to the other.

[jez9999]

Hmm, I see... but this is only going to apply if you can't channel those wall tiles from above?  It looks like a strategy designed to deal with only being able to mine the wall between dry and wet from the same z-level.

[Starver]

Yes, that's the approach.  Otherwise you'd just...


Set it up
≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈
#################
##XXXXXXXXXXXXX##
##.............##
##.............##
##.............##
##.............##

Then from the level above channel the whole front-line

≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈
##▲▲▲▲▲▲▲▲▲▲▲▲▲##
##XXXXXXXXXXXXX##
##.............##
##.............##
##.............##
##.............##

Then open all the floodgates
≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈≈
##▲▲▲▲▲▲▲▲▲▲▲▲▲##
##XXXXXXXXXXXXX##  |
##≈≈≈≈≈≈≈≈≈≈≈≈≈##  | (whoosh)
##~~~~~~~~~~~~~##  v
##.............##
##.............##


No messing about, really (except for maybe reflooring over the ramps, at ground level, to avoid 'misunderstandings').  Just not always convenient.


(If your river freezes in winter, BTW, just do all the work up to the edge when frozen... As long as you keep track of time and get enough done before it thaws...  Easy to get caught out.  Assuming you can avoid that, however.  And you might find it easier to replace a whole set of emplaced floodgates with a wide (but 1-deep) raising drawbridge, if your architect isn't otherwise occupied.  Not that you might need the floodgate-analogue for the connecting, but sometimes it's good to to have a disconnecting mechanism.

But then if you've got a freezing river then you can probably do most of what you want with the river, whilst frozen, without having to actually drain it first.  Shucks, it all depends on what you want to do...  Just giving the major options, and there are plenty more not so far mentioned.)

[jez9999]

Which ramps are you referring to?