So I've become convinced that Forgotten Beasts can pass through fortifications (at least ones in water). This is not the usual water pressure pushing creatures through, they pass back and forth through them with ease. With that in mind, and since they are building destroyers, any ideas on a filter for flowing water that will keep the buggers out?
Apparently there is a bug that prevents building destroyers from destroying buildings directly above them. So a floor grate that they must pass through from beneath should 'hypothetically' stop them.
This is what I've come up with, but I'm concerned it will stop the flow of the water making it worthless for power generation:
= Tunnel
H Channel
_ Floor Grate
===H
H _===
H H
H===
The reason the second stage is lower than the first is that in my experience (40d) in those situations water has not filled all the way to the top layer, but only to one layer beneath. That might not actually be how it works but it happened to me a long time ago and I've never cared to experiment with it.
Other ideas I had included having a pump draw water off the top of a fortification, but I'm not sure if that will work. since it leaves open space above the fortification and the pump is to the side, leaving it vulnerable to flying beasts.
Note: I'm trying to avoid perpetual motion here, since it's kind of lame (even if it is dwarfy).
Any ideas?
-oso