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Author Topic: River section freezing into ice dam  (Read 1565 times)

Paralyzoid

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River section freezing into ice dam
« on: October 30, 2021, 04:11:54 am »

I dug my new fort's entrance down at water level in a river in a canyon under a waterfall, on a 3x3 embark across three biomes. The map marked it as a hot region; so far, so good. When I embark two weeks into the first month, the river is flowing, as expected.

Come winter, a small section of river downstream freezes. But since I'm under a waterfall, the liquid upstream part keeps dumping water on the dammed lower section. I was able to stop my fort from flooding with a bridge, and eventually the rest of the river froze, stopping the flood.

I'd like to avoid burying my fort in ice every winter. Is there anything I can do to stop it? If I could stop the initial river section from freezing, I could avoid it, but I don't know how to do that.
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Moeteru

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Re: River section freezing into ice dam
« Reply #1 on: October 30, 2021, 07:40:53 am »

There are a few ways you could tackle the problem.
The simplest is to dig a diversion so that the river can flow to the map edge while staying within the same biome (so it all freezes at the same time). You could also dig under the freezing biome, since the temperature underground is always above freezing. You won't be able to dig the tiles right at the map edge so you'll need to designate them to be smoothed and then carve fortifications to allow the water to escape.
Another simple option is to dam the river upstream of the waterfall. If you use a raising bridge then you can link it to a lever and toggle it on and off seasonally. Since the whole river freezes this is very easy to do. Just make sure you raise the bridge before the water on top of it freezes, otherwise it will probably destroy your bridge.

If you want to keep the waterfall going during winter another option is to add an overflow drain to the canyon -- either a tunnel leading to the map edge or a minecart portable drain. The engineering involved in this approach is a bit more complicated, so for notation we'll say the bottom of the canyon is z0 and your fort's entrance is currently at z1. Build a wall across the canyon on z1 between the waterfall and your entrance, above but not blocking the water at z0, then put the portable drain on the waterfall side of the wall at z1.
The steady state side view looks like this, where # is a natural or artificial wall, numbers are water, E is your entrance, and D is the drain:
Code: [Select]
z4                     1234567777777
z3                     1############
z2                     1#
z1      EEE      #55D555#
z0  77777777777777777777#
z-1 #####################
I'm at least 80% sure that won't be able to flood your fortress.

EDIT: One more very dwarfy option is to use magma to stop the water from freezing. If there's magma 1z below the water it will stay above freezing. The only part I haven't figured out properly is how to get magma under the water at the map edge.

If you're feeling really dwarfy, both burning artefacts and caged creatures made of fire will also work as portable drains. They're too hot for your dwarves to handle though, so you can't easily move them once you've created them.
« Last Edit: October 30, 2021, 07:51:12 am by Moeteru »
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Thisfox

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Re: River section freezing into ice dam
« Reply #2 on: November 01, 2021, 09:05:45 pm »

I had it happen in one of my favourite forts, Alligator Creek. When the river froze downstream, the water would rise and the alligators would follow the flow into the fort....

My method was just to install doors over the lower entrance, and put in an upper entrance above the flood level which didn't necessarily need doors. So long as you forbid the doors in time each year, no problems eventuate. And it makes for some great stories. One year I didn't remember to forbid the doors (fun was happening) and really very little water was let in, the doors automatically close after the entry of each wandering fisherdorf. A few cleaners came through and removed the mud a few months later, and it was fine.
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Hans Lemurson

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Re: River section freezing into ice dam
« Reply #3 on: November 02, 2021, 02:26:20 pm »

I think that's pretty bad-ass, and am not certain it's a problem that needs to be solved.
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Garfunkel

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Re: River section freezing into ice dam
« Reply #4 on: November 04, 2021, 12:54:55 am »

This reminds me, can I make a functioning entryway through a waterfall? I really want to make a glass floor that goes through a waterfall as the entrance to my fort. I don't care if few dorfs die while building it but as long as I put bars at the point where the water is falling down, there shouldn't be any pathing problems or dwarves being swept away?
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PatrikLundell

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Re: River section freezing into ice dam
« Reply #5 on: November 04, 2021, 04:37:08 am »

Dorfs can't path through water that's more than 3/7 deep, and a waterfall probably generates more than that. Also, even temporary changes to a deeper depth can obstruct pathing (which means you have to calibrate the amount of water when building your dwarf washer [in my case I've used grates as floors]).
There is a risk of dorfs being pushed in all non blocked directions by flowing water, so to avoid death you'd need to block all potential falls within the area the water will spread to (and if the amount of water is too high you might still cause drowning, but at that point the entrance isn't functional at all).
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Thisfox

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Re: River section freezing into ice dam
« Reply #6 on: November 04, 2021, 10:17:13 pm »

I make bridges through home-made underground aquifer-fed waterfalls regularly. They're a full-body dwarfwash and mist machine. The walkways are actually not bridges, just 1-wide constructed floor footpaths, with a row of floor grates down each side, so that they are 3-wide altogether. They go right through the flow of the waterfall, and I've not had a problem with dorfs making it through the waterfall, and they love the mist. That said, my waterfall is only a few steps wide. Under the footpath and grates is a 2-z-deep channel (floored with statues for extra mist) which I make flow off the map. When I can, I make the walkway the only path to the tavern and food prep areas, so everyone gets a bath when they want food or drink. This is additional to a good clean aquifer-fed well with plenty of soap in a stockpile. Cleanest dorfs in history!
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Garfunkel

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Re: River section freezing into ice dam
« Reply #7 on: November 05, 2021, 08:24:35 am »

Thanks guys, sounds like floor grates are a better option than bars. It'll be two-tiles wide so not too massive.
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A_Curious_Cat

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Re: River section freezing into ice dam
« Reply #8 on: November 05, 2021, 01:23:08 pm »

I don’t really know what to tell you.  I’ve embarked several times in tropical broadleaf forests, and I’ve never encountered a situation like what you describe…
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Bumber

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Re: River section freezing into ice dam
« Reply #9 on: November 11, 2021, 05:59:14 am »

I don’t really know what to tell you.  I’ve embarked several times in tropical broadleaf forests, and I’ve never encountered a situation like what you describe…

Presumably the area that freezes is actually part of a temperate biome.
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