So, I started thinking about how to make lots of power within dwarf fort, preferably in a small package, since windmills are rather weak and without using any dwarf power.
So, I turned to the steam turbine for inspiration.
I give you, the Stream Turbine:
Upper Level
Lower Level
This design can be effectively extended indefinitely, and should, in theory, be extendable sideways into double turbines as needed, or to conserve space.
This one has 26 waterwheels in total for 2600 power. I wanted to make it long for proof of concept test and to make sure the water would do what I want.
The pressure valves before each intake prevent the water spilling up into the fort though the turbines, they also limit flow outright, allowing water to flow down to the far end of the turbine as well as the near end.
This particular design has an entire stream redirected to power it and the junction at the top also diverts to my cistern to the left, off the map to the right to ensure flow.
If one does not have a river on the map, you can make the output flow hook back into the input via 2-4 pumps that are directly connected to the drivetrain. This would not be able to be hooked up to a cistern and would need to source the water through an indirect means (either buckets or draining a pool into it.)
The pump section would look like this:
X X X | X X
X O P P I X
X O P P I X
X O P P I X
X X X | X
X X WWW X
X X X | X X
X = wall
P = Pump
G = Gear Assembly
| = Axle
W = Water wheel
. = Floor
I = Intake (1z hole, pump takes from here)
O = Output (1z hole, pump outputs here)
Granted, there's no that much to use power for, besides mills, rollers and pumps, but this could quite easily be set up to run pump stacks from nothing, without needing to send any dwarves down to the actual pumps in the stack.
EDIT: Fixed diagram