40d:Irrigation

Irrigation is the process of making ground suitable for farming by flooding it with water. Inside caves, rock cavern floor tiles that are covered with water instantly become muddy tiles, which you can then build farm plots on. There are many possible methods for getting the farm area muddy.

Reservoir Irrigation

Dwarf Fortress uses realistic water dynamics, including measures of water depth. A depth of 7 is full, depths of 1 will evaporate, leaving the stone wet and thus suitable for farming. Your goal in irrigation is to get a section of ground to be 1's.

The reservoir method involves building a small reservoir between two floodgates and a farming chamber at least 7 times as large as the reservoir. a reservoir of 10 tiles, for instance, can water a 7x10 chamber effectively. Water is let into the reservoir by lowering, then raising one floodgate. The other floodgate then releases the water into the farming chamber. It spreads around, then evaporates after becoming 1 deep.

Oldschool Irrigation

1. Dig from the farm plot to any source of water, but keep a single tile of wall between the newbuilt channel and the water. Also, dig a passage from the plot towards lower ground that'll serve as the water drain.
2. Build a door or floodgate, and three mechanisms.
3. Place the door in the channel. The idea is that it'll block the water from coming through when closed.
4. Build a lever and link it to the door or floodgate.
5. Pull the lever so the door opens. Send a miner to dig that last wall keeping the water from rushing in. Alternatively, have the miner dig a channel on the last wall from the Z-level above. The miner will dig out the wall without actually having to stand in the way of the water.
6. Ideally, here the miner will run like hell. The water is actually fairly slow.
7. Use the lever to close the channel once you feel you've got enough water to spread over the area.
8. Wait for water to drain out to at least 1/7 per tile. You can use grates and hatches to speed up this process.
9. Make farm.
10. Profit!

Pond Irrigation

Dig a farm room, and dig a channel one Z-level above it, creating a hole down into the farm room. Create a zone on the hole, and make it a pond. Your dwarves will attempt to fill it with water carried in buckets. As they dump water in, it will muddy the farm room floor. After it has been sufficiently muddied, disable or remove the pond zone until you need to irrigate it again. Dwarves can build farm plots in 1 unit deep water.

NOTE: Even though it works, this is probably the slowest way to irrigate a room since dwarves only carry 1 unit of water per trip. Especially if you don't have a more than one or two idle dwarves and buckets, or if the water source is far away. It also probably wouldn't work very well on larger farm areas.

Footstep Irrigation

As your dwarves walk through wet ares, they drag mud around with them. This mud can be farmed on. Through a little creativity, you can get sections of heavily-trafficked areas wet near your farms and your dwarves will irrigate them for you.