Dwarf Fortress Bug Tracker - Dwarf Fortress
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0011127Dwarf FortressDwarf Mode -- Environmentpublic2019-07-23 12:112019-07-24 08:36
Windows10 Pro
0011127: Shallow (1/7 and 2/7) water on vegetation tiles turns into ice walls during winter
According to the wiki, 4/7 water is the "Minimum height to make an ice wall when frozen": http://dwarffortresswiki.org/index.php/DF2014:Water [^]
I have a drowning hallway on my map which is in the process of being drained during the winter. The water drains onto my aboveground farm where the tile depths are mostly 1/7 and occasionally 2/7. When frost sets in, many of these tiles turn into Ice walls.
Uploaded save here: http://dffd.bay12games.com/file.php?id=14472 [^]
Current date in the save file is moonstone 26th. The frost sets in on moonstone 27th.
- open the save, it should already be on the farm level. Otherwise shortcut F2 will go there.
- leftmost room is where the water is draining
- let the game run for a short while and notice how the shallow water tiles turn into ice walls

This makes me think that either the wiki is wrong or that this is a bug. Considering that 1/7 water is less than knee-deep, seeing 1/7 water turn to a tile-high ice wall makes me lean towards it being a bug. Note: not all water tiles turn into an ice wall. Many of them turn into Muddy ice.
The only mention of this phenomenon I found on the bugtracker was in the comments of this bug http://www.bay12games.com/dwarves/mantisbt/view.php?id=1562#c6392 [^]
It was posted back in 2010. Maybe nobody ever bothered reporting this bug?
My other searches on the bugtracker did not yield anyone else reporting this.

Another somewhat related odd behaviour which might be a bug is that when the thaw sets in it turns all the "Muddy Ice" tiles into 1/7, 2/7 and 3/7 water.
I took the time to pause the game and step through until the first tick when the thaw sets in. It occurs around roughly 3/4th of the 2nd Obsidian (so about a month after the frost sets in). I don't know if this is intended behaviour or a bug. If it's the latter then it may deserve its own report.

Screenshots are included with the save.
- have an aboveground basin that contains water levels of 1/7, 2/7 and 3/7 but not higher
- wait for the temperature to drop so that water freezes
- you should see many of these water tiles turning into Ice walls
No tags attached.
related to 0001562confirmed lethosor Frozen shrubs display incorrectly when the ice melts 
Issue History
2019-07-23 12:11kermatNew Issue
2019-07-23 13:51LociNote Added: 0039447
2019-07-23 13:51LociAssigned To => Loci
2019-07-23 13:51LociStatusnew => acknowledged
2019-07-23 13:53LociSummaryShallow (1/7 and 2/7) water turns into ice walls during winter => Shallow (1/7 and 2/7) water on vegetation tiles turns into ice walls during winter
2019-07-23 13:54LociRelationship addedrelated to 0001562
2019-07-24 08:36kermatNote Added: 0039450

2019-07-23 13:51   
Thank you for the save. The tiles which freeze to ice walls all contain vegetation -- either shrubs or saplings. Just designating a (suspended) farm plot over the water tiles prevents them from freezing to ice walls.
2019-07-24 08:36   
Thanks for the reply. It never occurred to me that the vegetation was causing the ice walls to form. And thanks for the tip on preventing them to form.
I did some more testing and I think there are more factors that can cause an ice wall to form than the vegetation. If you go 1 z-level up, there are 2 hallways that drain onto a platform that's made of green glass blocks. When the frost sets in, (damp) ice walls slowly form on this platform as well.
I tested it by pausing the game as soon as I saw the river freezing, then stepping through and watching how the water behaves when it forms on the platform's surface.
a) if the platform tile was muddy ice with mud on top, a 1/7 water tile forms on it and on the next tick will turn into an ice wall
b) (uncommonly) if the platform tile is still a muddy green glass block floor with a pile of mud on top of it, a 1/7 water tile will form onto it and on the next tick turn it into a muddy ice tile (like the starting scenario in a). This can then continue until an ice wall has formed on this tile. This scenario happened once for me to test it. I guess the water randomly evaporated off one of the floor tiles right before the frost, leaving time for a new 1/7 water tile to form onto it and turn it into a muddy ice tile. Unfortunately I was not able to record or save this.

It doesn't bother me while dorfing but it seems like something worth mentioning nonetheless.