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[Albedo]

Standard perimeter defense has a 2-3 wide ditch channeled out (to prevent jumpers), and under-cut below it (to prevent climbers) and then fortifications overhanging from the wall, something like this...

Code: [Select]

  F
 W___   ___ -> (outside fort)
   |_____|
But if you want access to a river inside your walls, that creates a problem spot - can't channel it out without flooding the entire ditch (and allowing swimmers across) - so... how to deal with that?

I suppose you could terraform the river to flow down, under the wall, and then back up - but that could take years, and meanwhile you need ~something~ in place...

Do you just build up more overhangs over the river area, and call it good? Any other tricks or strategies?

[Loud Whispers]

The ideal would be to draw the water through an underwater channel and a pump, drawing the water through a grate (which cannot be destroyed from underneath). This would allow you to access the river without compromising the ditch at all.

[Albedo]

I suppose you could terraform the river to flow down, under the wall, and then back up - but that could take years, and meanwhile you need ~something~ in place...

[Drokles]

Are you really that desperate to have a river inside your fortress? Sure, building a through-way for the water to travel might be kinda-sorta complicated and lengthy (embark with 2 miners, 2 masons, and engineer and carpenter and you can probably complete it within 6 months) and it leaves a hole in your defenses, but it seems like a purely aesthetic choice.

You can't have both a river throughput and a perimeter ditch without a little effort spent on engineering and fortifying, so if you need a river underneath your walls be prepared to spend some time in a risky position.

So I seem to be misunderstanding what you are asking and I suspect there was poor communication, considering your classic "quote myself because I don't respect your reading comprehension and wanted a snarky way to say it" move.

Code: [Select]

0 = Wall
R = River
. = ground/floor
_ = open space/channeled tile


Z+1

000RRR000
..0RRR0..
__0RRR0__
..0RRR0..

Z+0
000RRR000
000RRR000
..0RRR0..
000RRR000



Is this what you were thinking about? The river is allowed to pass through both your channel and your wall, and because you constructed walls within the channel itself the river won't flood. You're essentially trading the ability to having flowing water run past your gates with the need to fortify a new weak spot in your existing masonry (since the walls flanking the river itself need to be made-anti climber).

[Loud Whispers]

I suppose you could terraform the river to flow down, under the wall, and then back up - but that could take years, and meanwhile you need ~something~ in place...

You wouldn't be diverting the river, you'd be siphoning from it. All you need is one tunnel going into the river, which takes a few days of mining to to.

[Albedo]

@ Loud W - I want the river, not just some water from it.  Siphoning would not achieve what I'm aiming for. If I just wanted drinking/fishing/pump-power water there are easier ways, of course.

@ Something like that, yeah.  I can see how I'd do it, just wondering if there was a more elegant way.  But overhangs and traps on top of walls it is.

Are you really that desperate to have a river inside your fortress?...  it seems like a purely aesthetic choice.

And yet it's not.  Small embark site (to avoid fps death), and the river goes dead-center, so kinda has to happen if I'm going to have anything above-ground.  And since I have plans to (eventually) make more complex traps for water-creatures to try to trap some of the wildlife that I hope to see there, that has to happen one way or another (not eager to construct/operate the traps outside the safety of the walls).


Can climbers path sideways along a wall, to a section not overhung? Or climb around the corner of a wall to get to a different face?

[Eldin00]

Climbers can definitely path sideways along a wall, or from one wall surface to another across an inside corner. I'm not certain if they can path from one surface to another across an outside corner, but I suspect they can.

[Immortal-D]

Should only be a minor engineering challenge.  Make some pumps at the portion of the river where your wall will extend, then install Grates in the now dry space.  Alternatively, if your river freezes in winter, you can wait and avoid the pumps.  The final option is to create an artificial river going through your above-ground base.  This will allow you to install the grates without a fuss, then you can simply channel the river to your base at your leisure.

[Sanctume]

Standard perimeter defense has a 2-3 wide ditch channeled out (to prevent jumpers), and under-cut below it (to prevent climbers) and then fortifications overhanging from the wall, something like this...

Code: [Select]

  F
 W___   ___ -> (outside fort)
   |_____|
But if you want access to a river inside your walls, that creates a problem spot - can't channel it out without flooding the entire ditch (and allowing swimmers across) - so... how to deal with that?

I suppose you could terraform the river to flow down, under the wall, and then back up - but that could take years, and meanwhile you need ~something~ in place...

Do you just build up more overhangs over the river area, and call it good? Any other tricks or strategies?

Code: [Select]

  F
 %%GW___   ___ -> (outside fort)
cWW_______|
You can add a pump through a grate and into c = cistern as the source of your river for however you want to do with it inside, safely?

[infrequentLurker]

If the river freezes during winter, dig a hole large enough for the river under  the river, with an access door at either end.  When winter hits, dig out the riverbed on either side, channel out all the river in between, build any retaining walls you need, then extend your fort wall / moat bits to where you  need them across the ex-river sections.

I'll edit in some demo code or something when I'm not typing on mobile, but the winter work shouldn't be too bad

[NW_Kohaku]

A brook is simple - stop digging a trench near the brook, and build a wall, instead.  A wall 2zs high with an overhang is just as good as a trench, it just takes longer to construct than it does to dig. 

A river is more complex, as you're going to need to drain it, first, to build up the defenses.  A simple-ish way to do this is to drain it like an aquifer into the caverns temporarily - in the spaces in front of the river, carve a shaft straight down to the caverns, and let that drain the river while you rush in and build your drawbridges or walls, then close off the drain to revert it to its new state.  With a drawbridge and a wall over the river, you can shut off inflow and outflow to stop building destroyers. 

(Also, keep in mind horizontal grates can be destroyed by building destroyers like Titans, so you don't want those to be your sole method of defense unless you grated the WHOLE inside area of your river, it's easier to stop them at the gates...)

Alternately, just do what I do, and get your water from aquifers.   I like rivers for the critters they tend to spawn, and the deep chasms they can create, but I don't touch them except to put bridges across them until I have completed a robust fortress defense, and only tackle them with things like obsidian-casting a dam so I can start putting drawbridges and cage traps in a natural riverbed.

[infrequentLurker]

Opted to make a new post instead, as it will be a little wordy and I made terrible Paint-quality pictures to go with everything.  Here goes.  As this is really only helpful if your river freezes during winter, here's hoping it does.  Otherwise it's kinda a waste of time 

The way I understand your embark to look is a bit like this:

Spoiler (click to show/hide)

a teeny embark area with a river running more or less dead center through where you want to build.  You seem to want an above ground fort with a nigh impenetrable moat despite the river.  On to that.

Spoiler (click to show/hide)

Build your walls as planned around the entirety except over the river.  You can build the walls OVER the river, but careful not to make things harder on yourself later.  Gather a few stones in stockpiles near the river, both inside and outside the fort, at any effected wall sections.  You have as long as you need to build these other wall sections.  Bear in mind that, other than the stone stockpiles near the river, basically none of this step NEEDS to be done by winter, which is not the case in the following part.

Spoiler (click to show/hide)

Dig a hole that stretches under the river AND under the planned ditch area.  Planned ditch area in that picture is based on a 2 wide gap, as shown in your opening post.  It is marked with red dots.  This ditch should be as wide as the river is, and the floor grates shown should be as well.  They will be above the head of any swimming building destroyers, so they cannot be broken there.

Spoiler (click to show/hide)

Once the water freezes, work begins in earnest.  Designate ramps from inside the ditch to breach the river bed.  Channel out the ice between the ditch entrances and build walls where shown to act as your ground tiles.  Be sure to wall off your ditch entrances and the channeled out river tiles before spring, or Fun will happen.  Less time sensitive after those critical bits is channeling out the overhang area for your ditch, so it will operate.

Spoiler (click to show/hide)

Come the spring thaw, the ice will melt.  The river will flow up to the wall you built near the ditch, pour down the ditch, then water pressure will push it back up the other side to the same Z level, and it should continue to flow from there through your fort.  Doing the same on the other side of your fort should have similar results, with the river flowing out.

Hope this helps! 

Spoiler (click to show/hide)

No seriously if i'm badly misunderstanding something here someone please correct me because it's been years since i played with water pressure and diverting rivers and i'm not 100% sure they keep their flow if you drop them through a U bend and I don't want to be telling someone wrong info and wasting a bunch of their time 

[Insert_Gnome_Here]

You could make the ditch 2z deep and only fill the bottom level, or do I misunderstand the situation?

[NW_Kohaku]

You could make the ditch 2z deep and only fill the bottom level, or do I misunderstand the situation?

Well, for starters, this person wants a natural riverbed, so if you dig 2z deep into a river, you're going to have the river flood the whole thing up to ground level. 

A 2z tall wall with fortifications on the second floor to prevent climbers (and probably some paved roads out front to stop trees) can be built over the river, which is a help, but not entirely enough, as all titans are amphibious building destroyers, if I'm not mistaken. 

Now, some people have suggested filling in walls through the water, and having an underground connection such that there is a z-level shift that lets hydrostatic pressure refill the riverbed at appropriate points, which could work except that if there is an alternate path to the grates, it can still be destroyed from underneath, which will be the case if the player does not completely cut off the entrance within which the player wants to fight the titan from the courtyard that has the grate in the first place.  (Although possibly, one could make a deeper underground bypass, and have a grate completely surrounded by walls on that z-level, which may prevent swimming building destroyers, but may not.)

Hence, again, the best bet may be to simply find a way to dam the river (if it freezes, this is easy), and build a drawbridge (and possibly a grate behind the drawbridge) at every point that the river crosses the walls, since those are at least guaranteed building destroyer-proof, although they may require some manual cut-offs, or else something clever, like a bait animal behind a window right beside the river that trips a pressure plate upon water contact as a "building destroyer detector".

[infrequentLurker]

Curious - if, in the design I posted, you put a second floor grate above the second ramp, such that the only path to the floor grate in the picture went through the hypothetical second floor grate, would that fix anything?

Also, while opening post did mention Albedo realized he could do what I suggested and I only realized that later, this would at least be a single year solution as opposed to the multi year project he was worried about.  _{I seem to be that bad combination of eager to try to help and really bad at the actually being helpful in any way}