40d:Reservoir

A reservoir lets water flow into your fortress a little bit at a time. This lets you take advantage of lakes without tapping all of it at once, or get water from a river without flooding the whole fortress. You can get water from the ocean, but it's not drinkable.

Operation

Open the outer floodgate to fill the reservoir. Close it once there's enough water inside. Open the inner floodgate to release the water. Never have both open at once!

Making a reservoir

Planning

Plan carefully where you want the water come from, and where you want it to go. Building next to a body of water is easiest. You can have the water flow down a staircase, or make channels for the water. Block off any corridors that connect to the water output. A simple door right next to flow will prevent water from pooling in the corridor.

Also, you need to place two levers to control the flow of water. It is easy to forget which lever connects to what. You might want to build a lever room nearby. Build levers parallel to the floodgates.

Digging

Mine out an area like this, one level below the ground. The diagonal kink is important! The area above it will be the reservoir proper. It can be any size you like, but make sure it only connects to the rest of your fortress through that diagonal opening. Water will flow out from below that kink, so make sure there's no hallways below that you don't want flooded.

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Floodgates

Build the upper floodgate at the very end of the reservoir chamber. Since dwarves don't build on the diagonal, there's no risk of dwarves getting trapped. Once it's in place, connect it to a lever.

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Build the other floodgate just behind the kink. Dwarves don't build on the diagonal, so this keeps your dwarves from trapping themselves. Connect it to another lever.

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Input channel

From above, channel into the water source.

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Output channel

You can have the water just flow down the stairs, or dig a channel just outside the outer floodgate. This cuts off access to the reservoir, so you can't re-jigger the floodgates. Hopefully, you will not need to, but you can build a horizontal grate or bars to make the channel walkable but still allow water to flow through.

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Variations

Deeper reservoir

If for some reason you need to build a reservoir deeper underground, or further from the water source, you can connect the water source to the first floodgate by a stairway or tunnel. Add another kink before the first floodgate to avoid trapped dwarves.

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Fish-proofing

Draining from a large body of water can allow large and potentially dangerous aquatic creatures into your fortress. Installing a grate or bars across the water flow can keep them out. Note that bars will allow vermin-size creatures though, and grates do not. You can use a fortification too, but the slows down the flow of water.

Re-directing water flows

It's possible to re-configure a reservoir to channel water in a new direction. You can construct walls and floors to block water, or place doors and hatches.

Doors vs floodgates

Currently, you can use doors and floodgates interchangeably. ^{v0.27.176.38c} This is expected to change in the future, so your doors might start leaking in the future.