Krosan was an elite before, the long standing heros bug caused him to revert to just Marksdwarf. I believe almost all our marksdwarfs are elite though (Great Marksdwarf or better).
Yeah, I think I actually got that notification several times.
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As to the aqueduct, the flow from the aquifer is not as strong as I expected. So now not only has the water's rate of expansion in the reservoir reached equilibrium with the rate of evaporation, the flow from up top has slowed to a trickle. [By the end of Granite it's almost entirely dry, even though the gates are still open.]
I wish I had tested this sooner. :/
It should be relatively easy to fix, if you are feeling up to it, though by the time it is fixed the lower canals will probably need brush clearing.
1) Turn off the flow from the aquifer. The southernmost lever on floor |95|, at hotkey F6, will do this. Doing this will allow water to fill up again in the well and first stage, pushing it further before running out of pressure.
2) Wall off most of the southern end of the reservoir room on floor |0| (just below the hospital, hotkey F5), so that inflowing water is forced west to the ramps along the far wall. Pave the soil along that route (there are hidden, forbidden stones already in the room).
3) As soon as that wall and paving is finished (put a door in it somewhere for maintenance, just be sure to forbid it when done), reopen the floodgates. Or let the water build up a little bit longer, up to you. The second option is probably best, and just means you should definitely get the axes out before opening the floodgates.
Also, the flow to the wells is pressure locked, so it will not overflow once the water reaches those channels. We just have to get it that far, and remove any obstructions.
Or, alternatively, try to increase the water flow (it's low enough by the aquifer that you could probably build something there now). Or find a different means to getting water to lower deathgate after you've sealed the upper levels with magma.