40d:Channel

A Channel is a method of digging mostly to aid the moving of liquids, such as water and magma, from one point to another. While it is a convenient way to move liquids, it can be used for other creative purposes.

Building Channels will remove the floor of the current Z-level AND mine the walls in the Z-level below. See the digging article for a more detailed explanation.

Dwarves can not walk across a channel (as there is nothing to support them). However, you can refloor over a dug channel using b -> C -> f to allow dwarves to walk over it, while still maintaining the tunnel beneath. If you want to allow fluids to flow into a channel from above and dwarves to walk over it, you can put a grate on top of a channel, which only fluids will pass through.

In layman's terms: digging an area will carve out a tunnel in the rock to crawl through, whereas channelling an area will remove the bottom of the tunnel as well, creating a Trench of sorts.

Designating channels over existing downward stairs will make the dwarves remove the staircase, working from the level below.

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.

Hint

When building channels diagonally, a single line is enough - water, like creatures, moves in all 8 directions (+ z-axis).