40d:Irrigation

Irrigation is the process of making rocky ground suitable for farming. This is usually done 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.

Dwarf Fortress uses reasonably-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 1/7s.

Dryland Farming: farming without irrigation

Some locations have layers of soil a few z-levels thick. It is not necessary to irrigate soil in order to grow crops on it; it is possible to build a farm plot directly on any soil tiles, although the dwarven crops such as plump helmets can only be grown in a subterranean plot. Likewise, a farm plot built on any tile marked Above Ground can be used to grow outdoor crops such as prickle berries. This method obviates the need for irrigation entirely, so is recommended for newbies.

NOTE: Sand is a type of soil in Dwarf Fortress, so you can build farm plots on sand.

Easy Irrigation

dig from the farm plot to any source of water, but keep a single tile of wall between the newbuilt passage and the water.
Dig a passage from the plot towards lower ground or a pit, to serve as a water drain (this stage is not 100% necessary, but means you don't have to worry about having too much water and so is recommended).
Build a floodgate, and three mechanisms. (If you're worried about delay, use doors instead of floodgates.
Place the floodgate in the passage. The idea is that it'll block the water from coming through when it's closed.
Build a lever and link it to the floodgate.
If you are building a drain, follow steps 3-5 again and place the second floodgate at the entrance to the drainage channel, linked to the second lever.
Pull the first lever so the gate opens.
Send a miner to dig that last wall keeping the water from rushing in.
Alternatively, have the miner dig a channel (d,h) on that last wall from the Z-level above. This is much safer, since the miner will dig out the wall without actually having to stand in the way of the water.
Use the first lever to close the channel once you've got enough water to spread over the area. If you have a drain, you can now let any excess drain off using your second lever.
The water should now cover (or have covered) 1/7 of each tile.
Wait for the water to evaporate and/or drain off (Dwarves can built farm plots in 1/7 water, so you don't need to wait).
Enjoy your newly irrigated land.

Reservoir Irrigation

The reservoir method involves building a small reservoir between two floodgates and a farming chamber about 7 times as large as the reservoir. A reservoir of 12 tiles, for instance, can water a 70 tile 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.

The reservoir may be built above the plot to be irrigated with a hatch or bridge in the floor, to one side using floodgates, or below and pumped upwards. Note that bridges, in their default state, will block water from falling between levels. The large surface area you can get this way can make the water spread over your farm area much faster than by using floodgates.

It is possible to achieve the same result using a natural pond as the water reservoir. Doing so is easier in the short term but it is not advised if you want to keep replenishing your reservoir for other uses, such as well(s), for natural ponds have a very finite amount of water available. On particular maps, natural ponds can replenish themselves at the beginning of each spring.

Worked Example

To create this irrigation system, you need:

A large growing room.

The large room can be any size. (For this example, we will use a 24 by 24 size room.)

An adjacent smaller filling room that will be filled with exactly the right amount of water.

To calculate the size of this room, see below.

A water supply line such as a tube leading to a water source.
Lever-controlled doors or floodgates connecting the large room to the smaller one, and the smaller one to the water supply. Doors are preferred as you don't need levers for your dwarf to pass. (However, if you're paranoid or your dwarves are particularly dumb, you might want to lever them anyways. The creator of this method (GreyMario) recommends using doors because they have no delay when triggered.)

Calculating Room Size

There are 576 (24²) floor tiles in the large room (L). The small room (S) must hold enough water to cover the large room, the small room, and the space occupied by the door(s) (D) in between with 1 unit of water. Each tile of the small room can hold 7 units of water, so:

S = (L + S + D) / 7

-or-

S = (L + D) / 6

577/6 = 96 1/6; rounding up, this gives 97. This is the number of floor tiles in the smaller room: a 9X10 room with 7 extra tiles. Be aware, however, that if you make your "large" room too large, some of the water from the "small" room will evaporate before reaching the other end, and you will not have enough water to coat the floor. This behavior was observed in a room of 42X35 tiles.

Now, get digging. The water supply connects to the smaller filling room by a 1-tile hole where a door or floodgate will go. The filling room connects to the growing room the same way, and the growing room needs a door too. Remember to have the doors in place before breaching the water source and flooding the water supply line!

When you do breach the water source, immediately forbid the first door your miner runs through (see, this is why we use doors), which should be the door closest to the water source. Don't bother forbidding the other two. Link all three doors to three separate levers and test the system. Close the door between the filling chamber and main farm area and open the door that leads to the water source. When the filling chamber is full, close the door to the water source, close the door leading to the farm, and open the door between the farm and filling chamber. The water should spread out and coat the entire farm in a thin layer of water. At this time, plant your farms and begin the wait until they yield products.

Pond Irrigation

Dig a ramp down from a tunnel, preferably near a well or other water source, and dig a farm room next to the ramp on the lower level. Create a zone above the ramp, 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. It's especially slow if you don't have 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. It works great with constructed staircases for creating outdoor farm plots where there's an occasional stone in the ground though.

NOTE: Digging a ramp or channel down from the surface will mark the tile below Outside. This means that cave plants will not grow there.

Pump Irrigation

If you have access to wood, stone floors can be irrigated conveniently from a water source on the level below, by use of a screw pump. Simply dig a channel to access the water on z-1, install a Screw Pump and set to Start Pump Manually (Enter). Any dwarf with the 'Pump Operating' duty active will quickly pump enough water to irrigate a large area (so rapidly that irrigating other rooms becomes a concern!). This can be improved by installing a second pump to draw water out of the room, allowing you to rapidly drain the room in the event of over-filling.

Wave Irrigation

Although seawater is unfit for carrying to your farm in a bucket, areas muddied by seawater seem to be farmable. My favorite method of achieving this is building a farm room under a beach and making a hole in its roof, closable with a hatch, to let waves in. Also pumping water seems to desalinate it, so pumping it to your farming room seems to work fine.

Outdoor Irrigation

As of v0.28.181.40d, outdoor irrigation doesn't quite work. You can turn outdoor rock into mud, and you can build a farm plot on it, but the resulting plot won't allow any seeds to be planted in it. The specific message is "No seeds available for this location". An "outdoor" plot can be built on indoor soil by opening up the ceiling, and optionally flooring it over again, but this won't work on indoor mud.

Underground River Irrigation

Underground rivers are often what makes living in freezing climates possible, because they don't freeze over. Its very easy to tap one if you know what you're doing. Once you've located it, pick out a good spot for your farm room and dig it out. Make sure you're on the same level as the water; that is, where the actual water is located, not where the 'Open Space' is. Channel out one tile in the farm room and replace it with a floor hatch. Dig a narrow tunnel to the underground river and put a wall grate and a floodgate in it. Link the floodgate and hatch to seperate levers. Dig one level down and dig a drainage shaft from the tile below the hatch to the point where the river 'drops'; you'll see a 5x5 area of 'Open Space'. When your ready, dig a small tunnel and channel out the floor so you breach the river below and send it into your grate and floodgate. Open the floodgate to water your crops, close it when you're done and open the hatch to drain.

NOTE: The grate is necessary to filter out nasty creatures that might otherwise come in with the water.

De-Irrigation

On soil, building a wall and then removing it results in furrowed soil. However, on mud, the process results in rough but dry rock. This may be a bug in v0.28.181.40d, however.

Further Testing

The type of rock is changed(at least in v0.28.181.40d) - perhaps to that of the rock wall below? What if there is no rock wall below?

- it would seem this only affects the non-native stone of a layer, and changes it into the native stone, it definitely does not turn it into the rock type in the layer beneath if it is another non-native stone. (non-native means stone like orthoclase or microline)