A channel is a hole dug in the ground or wall which will mine out the z-level below too. You can use long channels to act as moats, to move liquids such as water and magma from one point to another, and other creative purposes. With this option it is possible to either select floor tiles or 'full' tiles. When channeled out, the floor (as well as a wall if it exists) on your layer will be removed and the tile on the layer below will be mined out. Creating a channel could be described as "strip mining".
In layman's terms: mining an area will carve out a tunnel in the rock to crawl through, whereas channelling an area will also remove the bottom of that tunnel and make a second tunnel one level below, creating a Trench of sorts.
Digging a Channel differs from version 0.28.x.x - it creates a ramp on the level below instead of an open space. Remove the bottom ramp by esignating it to be removed ( ). Channels dug above a layer that has been dug out will not create ramps.
One consequence is that the dwarf can now channel straight down for as far as he likes. This will happen even if you don't intend it - the dwarf will walk down into the channel he's just made, and dig the next channel down, seemingly in preference to digging a tunnel to access that next channel from the side as perhaps you'd intended. As there is (usually) no surface adjacent to the channel, the dwarf stands atop it and digs under his feet (though this depended on psychiatric "confidence" in 0.28.x.x - does it still?Verify), usually falling to the next level down, usually leaving him stunned, sometimes bruised, but not greatly harmed. This can lead to fun, and it also gets your elevator shaft dug in a hurry, with the dwarf emerging at the bottom atop an absurdly large pile of stones. (Pity they haven't invented the elevator...)
Channels, once the ramps have been removed, can be used to create moats which non-flying enemies will be unable to cross. Note that if you designate a large area for channeling the ramps in the middle will be automatically removed while the ramps at the edges will remain to be removed manually. This allows you to very quickly build large artificial lakes.
Some notes on dealing with channels:
- If you want a channel with no exits at all, then you will have difficulty, as dwarves will only be able to remove the exit stairs/ramps from inside the channel. The easy option is to wall off a separate exit area. If this offends your aesthetic sense and you are willing to go to the effort, there is another solution: Make a constructed ramp to get your miners out, then collapse a tile of constructed floor to reduce the ramp to rubble (which you can then hide). Another way to create a channel with no exit is to use a staircase in the center of the moat not adjacent to the edge but accessible by a floor tile or a bridge. Remove, raise or accordingly retract it after your last miner has left.
Preventing channel access:
- You will sometimes want to dig a channel without risking your dwarves entering it (e.g. fun with magma). This can be achieved if you (ab)use the ramp access rules. If the tiles adjacent to the critical channeling tile are either impassable or have empty space below, then the ramp will not be accessible after being dug, so your dwarf will remain safely on the upper level.