|This article is about an older version of DF.|
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.
Because it has the potential of removing two layers of wall and one of floor, channeling has the potential to be the fastest mining method. However, be careful to ensure that multiple miners working in the same area do not cause each other to become stranded.
Open the esignation menu and select cannel. Mark out the area you want to create as a channel - be careful to check the z-level below too! When building channels diagonally, a single line is enough - water, like creatures, moves in all 8 directions (+ z-axis).
The channel designation can be used to dig upwards. If a square is designated to be channeled and the z-level below has either a ramp or upward stair the miner will stand on that and remove the roof. In the same manner, designating channels over existing downward stairs will make the dwarves remove the staircase.
Designating a channel on the level underneath an existing channel is the way to dig deep pits or well shafts. Designating an adjacent up/down staircase is the easiest way to give access to the miner who will dig the shaft.
To swiftly channel out large areas multiple Z-levels deep, the fastest way is to designate it level by level as ramps from top to down. After it finished you'll need to remove leftover ramps at the bottom with remove stairs/ramps designation. You may consider leaving a single column of stairs leading back to the surface, removing it the once you're done, to aid miner access; in any case, this method requires that you give your miners a way out of the bottom level once they've finished.
If the area you wish to channel is many Z-levels deep, it can be more efficient to build a construction shaped like the hole you would like to create on top of a support at the highest level. If the support is linked to a lever, and the lever is pulled, the constructions will fall through every floor until hitting solid material. Be sure to keep dwarves and valuable items clear of the falling debris.
Dwarves simply *love* to stand on the wrong side of the channels and dig themselves onto isolated islets. To avoid this, find the longest bisector of the tunnel, channel along it, and then continue expanding by adding one line at a time to each side of the initial trench. They appear to want to stand to the left of the channel being dug, if possible. Consider this if collapsing the floor.
To move liquids simply connect one end of the channel to the liquid source, and the other to your desired destination. You will probably want to leave digging through the last square prior to the liquid until all your floodgates etc. are finished. An unexpected flood can set your fortress back several seasons.