I just pulled the lever on what I guess is my first mini-megaconstruction.
I embarked on a tropical map with a river that was around 20 tiles wide on average. Also, there's a magma pipe nearby. So I built a dam. A hydromechanical dam. Sixteen waterwheels providing 1600 units of power.
The first step was to build a magma pipeline from the pipe (which was exposed) to the river two region tiles away. Then I built a windmill-powered two-Z-level pump stack to pump the magma into the pipe … and discovered my map is apparently windless. Unless there's some issue with building a windmill one z-level above the ground? Does wind only work at ground level?
Anyway, my dwarves threw a couple waterwheels into the river and ran an 80-tile-long axle to the pump stack, dodging hippos and rhinos and fire imps. (There were two grass fires during construction. Order everybody in, wait for it to burn out. Twice. Booooring.)
I pulled that lever, and magma flowed into the river, damming it nicely. It took two years for the pipeline to drain and the magma that pooled on the surface on the dam to evaporate, though. I could've thought that one through better.
Anyway, I hollowed out the dam, installed the hardware and stuff, and just pulled the lever. I'm getting 1600 units of power … at 32 frames per second while the downstream half of the river refills. Oy.
Now I need to think of something to do with the power. Apart from driving the pumps that provide, er, "heating" to my eventual nobles' suites, of course.
Oh. My dwarves have been eating carp and tigerfish for the past two years. There was a BIG butchering party when the downstream half of the river drained.