40d:Dam

A dam can be built across a river or brook. This has several uses:

• Stop a river from flowing altogether
• Modify a river's path
• Create a pretty lake or functional reservoir
• Create water-based traps

Dam construction

There are two easy ways to construct a dam. The first, and quickest, method is only possible if your map freezes during winter. Simply dig out a thin section across the river and build a wall out of wood or stone, blocking the path of the river.

The harder way is to drain the river (e.g. by building a sizeable lake which the river will take some time to fill). Once the river has been drained you may have to dig into to river bed to be able to place buildings. It will look a bit like this:

Once the dam has been built, when the water comes back it will fill up the gap as far as it must to let the blocked water flow further. If you build your dam up to the level of the river the water will stop at the dam (it will not overflow). Since this defies logic it may be fixed in future releases.

You can create a massive flood if you build a dam out of floodgates and open them all at once.

An alternative method to this is to use a large number of pumps to move more water out of the river than can be replaced using screw pumps. For a river with a width of 4 tiles, you will need three on either side pumping it into channels or tunnels, ideally off the map, a waterfall, or somewhere where flooding will not be a concern. While the pumps are operating, it will be drained enough to build the dam.

A similar technique can be used to create water "holes" in large bodies of water, such as lakes or even the ocean. Build a ring of floors at the water's surface, and line it with an immense number of pumps, facing out of the area you wish to drain. The pumps should be able to push out water faster than it can come back in, allowing you to build a dike in this area. This is hazardous if the water is more than one z-level deep, since it's highly likely a dwarf can drown.