40d:Irrigation

Irrigation is the process of making rocky ground suitable for farming. This is done by flooding it with water; when the water evaporates, the tiles are labeled as "muddy". This is also called muddying the floor, as the dry floor tile is then a "muddy <type of stone> floor". Inside caves, rock cavern floor tiles that are covered with water instantly become muddy tiles, which you can then build farm plots on.

Once muddied, ground never needs to be re-irrigated, unless the muddying is removed by dwarven construction (see below). "Muddied" tiles are not technically wet once any actual water is gone, and damp stone or soil (from nearby water sources) will not cause muddying.

There are several methods for getting the water onto (and then off of) the floor tiles. 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, so it will evaporate to muddy. Usually it can't be avoided that part of the section will be flooded with higher levels, but water will disperse and eventually evaporate. If the water level gets too high and no 1/7 tiles exist (or not for long, replaced by shifting 2/7 tiles), the water will not evaporate.

Smoothed floors that are muddied will remain smooth, however if/when shrubs or tower caps grow, that tile will then revert to a rough stone floor tile. Constructed floors that have been muddied will not prevent the growth of shrubs or tower caps.

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 whip vine. This method obviates the need for irrigation entirely, so is recommended for newbies.

(* Note: Any type of soil is the same for this purpose in Dwarf Fortress, so you can build farm plots on sand, mud, ooze, clay, whatever.)

Once the proper requirements are met, Tower caps will grow on any unimproved (i.e., non-irrigated, non-farm plot) underground soil, but very sparsely - irrigating is always recommended for tower cap farms.

Pump Irrigation

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 pump and set to Start Pump Manually (q + 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, or by other creative designs.

Pond Irrigation

Dig a channel tile down from a tunnel, preferably near a well or other water source, and dig a farm room below (and preferably around) the channel tile on the lower level. Create a zone on the channel tile above, and make it a pond. Your dwarves will automatically attempt to fill it with water carried in buckets. As they dump water in, it will muddy the floor on the lower level, spreading out to surrounding tiles once the second bucket load drops. After it has been sufficiently muddied, disable or remove the pond zone. Since dwarves can build farm plots in 1 unit deep water, you can place your plot right away once all desired tiles are covered.

Due to the low demand in infrastructure, items and water management, this is one of the fastest and the safest way to irrigate a floor. Dwarves carry 1/7 unit of water per trip. It's slower if the water source is far away, but still very manageable compared to digging an aquaeduct and building floodgates or even pumps.

If you need to irrigate a larger area, larger than 3x3 - depending on distance to the water source - you may need to dig several channel tiles. The method also works great with constructed staircases for creating outdoor farm plots where there's an occasional stone in the ground.

NOTE: Digging a ramp or channel down from the surface will label the tile below as "Outside". This means that underground plants will not grow there.

Wave Irrigation

Although seawater is unfit for carrying to your farm in a bucket, areas muddied by seawater seem to be farmable. One favored method of achieving this is building a farm room under a beach and making a hole in its roof, closeable with a hatch, to let waves in. Alternately, water is desalinated by pumping, so pumping it to your farming room will work if the water does not pass through an aquifer.

Outdoor Irrigation

Outdoor irrigation of rocky locations is possible using similar techniques, though you may have to construct walls to make water channels, pumps to get it out of rivers, and/or stairs up to pour water down on top of a pond zone. This will serve to make muddy tiles suitable for a farm plot; however, be warned -- in mountain biomes (where you are most likely to feel the need to irrigate outdoors), no outdoor seeds will grow in rocky locations anyway. (The specific message is, "No seeds available for this location"). However, these techniques do work just fine for muddying individual rocky tiles breaking up your farm in a non-mountain biome.

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^[Verify]. If the farm plot includes at least one soil/grass tile, this does not appear to happen.

De-Irrigation

Muddy soil can be cleaned up by building a dirt road on top of it. Muddy stone can be cleaned by building furniture (such as a bed or statue) or a paved road on top of it.

Design Examples

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.

Easier, safer irrigation

Here's a relatively safe and simple irrigation plan. As shown it's set up for an underground tower cap farm, but can easily be adapted to any level, surface or deep underground.

This is a passive system - it's never connected to the river, so it won't do anything unless manned by a dwarf, and it doesn't need any levers or floodgates to work - or to stop working. Unless you forget about it, no flooding should occur - and even if you do and it does, it's foolproof to stop.

Dig a tunnel from next to your river (don't breach!) to roughly the middle of your future TC farm, and up to it. 2-3 tiles wide should provide a good, controlled rate of flow from one pump, and ramps or stairs work fine for connecting levels.

Now, the trick is to use a pump on the surface level to provide the water, the pressure, and the control. Build your pump next to the river - (if it's a brook you'll have to channel 1 tile of the brook for the inflow - don't breach the tunnel!). For the outflow, build a retaining wall around the start of your irrigation tunnel.

It will look something like this:

surface level      __   xX(   )__________________________________ 
river water level    ~~~   |_|== |            ____TC_   _Farm____ 
water -1                       |_|===================|_|          
 
       ~~~ = river/brook*
        xX  = pump (pumps from left, from west in this diagram)
      (  ) = small walled retaining area on surface, to contain outflow of pump.
       |_| = channels, ramps, and/or stairs up to next level
       === = underground tunnel for water flow

(* This can work from a pool, but that is not an infinite source of water. Plan accordingly.)

Order the pump to "start pump(ing) manually" (q + Enter), a dwarf will respond, the retaining wall will try to fill but will drain down, the tunnel will fill, and the water will start welling up out of the far end.

When at least 1/7 depth has covered almost the entire area (yes, you have to keep half an eye on it, so you are the sole point of failure!), go to the pump and tell it to stop pumping - order it deconstructed and then cancel that, and/or Activating the dwarf will do fine and be immediate, no lag.

The water settles out and evaporation begins immediately. You can then seal up the tunnel or ignore it as you choose (even if you later, accidentally, breach the river/brook, the u-bend won't cause flooding if the irrigation is on the same level, as shown above.)

If the layout of your underground rooms prevents a one-level tunnel, you can easily drop it down additional levels - it's the difference between the inflow and outflow that matters. Avoid single-diagonal paths - keeping the tunnel 2-3 wide will always provides pressure and flow.

One drawback is that the lower tunnel will stay full of water, which can be a small problem if you ever, later wish to expand the tunnel for other purposes. One or more drawbridges, acting to block the passage, will allow you to seal it later for easier expansion projects, and, if your first effort, is a good safe opportunity to practice in a non-critical situation. (See also: fun.)

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.

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.

An easier method is to find a location where the cave river falls for more than three z levels and simply build a screw pump to suck the falling water from midair.

        <- Empty room which will be used to farm.
##╬%╬## <- Screw pump with doors on each side to keep the water from possibly washing the pumping dwarf into the river.
###%###
##~~~## <-- Water is falling here.
#     #
#     #
#     #
##   ##
#######

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 microcline)