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[Rekov]

I was reading the dwarf fortress wiki and I came across something I hadn't considered before:

One of the first challenges presented by a freezing climate is the lack of water in any conveniently drinkable form. Along with trees, water may be the hardest resource to obtain. The ice chunks left behind while digging through ice cannot be melted into drinking water. There are several ways to approach a freezing area. One of them is embarking with a volcano in site, utilizing the natural obsidian surrounding it to create magma-safe floodgates and mechanisms to effectively melt ice.[1]

I hadn't realized that Dwarf Fortress' temperature calculations where actually this sophisticated. Is this even possible? Assuming it is...

How close to the frozen water tiles do I need to get the lava for it to melt? Is it possible to 'reactivate' a river so that new water flows from off map? If not, any water on the surface would basically be finite, unless you had some way of thawing it, then freezing it when it iss at 3/7 depth or whatever, and thawing again.

[Khalari]

I know magma does melt ice, not sure exactly how close it needs to be.

[Pirate Santa]

I once tried melting a frozen river by digging a replica on the next level down and filling it with magma.
Some of it thawed, the rest did not. Couldn't figure out why.

[gchristopher]

I just did this in 0.42.04 and the answer is: "kinda, but not the way you hoped."

Magma flowing 1 z-level under a frozen river will thaw the river above it, but not the floor of ice 2 z-levels above. That presents some problems:

- It has to be flowing to trigger the temperature recalculation that thaws the water. "Flow" is when liquid from one tile moves to an adjacent tile with a lower liquid level. So just filling it up to 7/7 magma won't do it. It has to be partially filled so magma is flowing somehow. Filling halfway between two levels will do it, so you have 5's and 6's of magma level moving around randomly under the river. Otherwise, the water thaws once when you pump in the magma, then refreezes and stays frozen. Also, this will probably be a big FPS drain.

- The floor of ice over the river won't thaw, so you can't get at the water easily. You can channel down through the ice floor to the water underneath, but the shell of ice over the water will re-appear with the freezing cycle.

[Bumber]

It has to be flowing to trigger the temperature recalculation that thaws the water. "Flow" is when liquid from one tile moves to an adjacent tile with a lower liquid level. So just filling it up to 7/7 magma won't do it. It has to be partially filled so magma is flowing somehow. Filling halfway between two levels will do it, so you have 5's and 6's of magma level moving around randomly under the river. Otherwise, the water thaws once when you pump in the magma, then refreezes and stays frozen. Also, this will probably be a big FPS drain.

Fluids can also flow while moving off the map under pressure. If you seal off the intake and outtake, the isolated section gets stuck flowing with no FPS drain. I'm unsure if it triggers temperature changes or not.

[PatrikLundell]

If you can thaw the river from beneath, you should be able to drain the water sideways. Before you let the magma in below, you'd dig a drain to your cistern from beneath two tiles beside the river and then dig out the tile beside the river while keeping the roof. Water will flow sideways and down, and since the tile beside the river is "underground" it shouldn't freeze.

Will the alternative approach of having the magma on the tile above the river work to melt it as well? I'm thinking about making a floor on top of the river and then walls on top of the banks to make a trench for magma to flow in.

[gchristopher]

Fluids can also flow while moving off the map under pressure. If you seal off the intake and outtake, the isolated section gets stuck flowing with no FPS drain. I'm unsure if it triggers temperature changes or not.

You're talking about permanent flow flag for the affected tiles? That's a really interesting question. I've only ever used permanent flow to keep water wheels powered, and never tried to get perma flow on magma. I'll try it!

Will the alternative approach of having the magma on the tile above the river work to melt it as well?

It should. I think temperature calculations are applied to all adjacent tiles, including up and down.

[Plex]

I thought about trying this, but I was worried that the water would evaporate into steam.

I'm an old noob that hates trying new things, probably why I get tired of my fortresses quickly.