Recently I finally started to really begin playing DF in earnest.
I have used LNP and followed some tutorial but with a world of my own, doing things roughly in the order of the tutorial's suggestions. My fortress lies relatively near its parent civilization's holdings, in a hill next to a forest. The temperature is hot.
Everything's going relatively well. The LNP's population cap doesn't seem to do anything, and now I have 280 zwergen in my fortress, in year 7 or 8 by now. Luckily I have a relatively good PC so I can run it relatively fine. No goblins or other invaders have ever appeared. One minotaur showed up, and promptly got caught in a cage trap.
Thus my biggest problem has been the lack of water. There is no river, no aquifer (due to following tutorial's "don't get aquifer" orders) and the few murky pools on the surface dried out on first summer - they eventually watered up again in year 4 or something, but for many years I had no water anywhere. For some reason even though I am damned certain we never were at "0" drinks, alcohol ran out at one stage, and something like 60 dwarves dehydrated to death, which made some interesting carvings.
Amazingly, there was no tantrum spiral or no sort of collapse of my fortress at all, which everyone always speaks about.
Eventually I dug down to the caverns, and there was water. I remembered I could finally do a well, and after checking the guide that the distance to the water doesn't matter, I dug an extension to my dining hall, and marked up a spot that was directly above a source of water.
This source of water in the caverns was about 55 z-levels down from the dining hall.
I channeled out the marked spot once. A dwarf made a hole, and now I had a downwards triangle and a hole on the lower floor. I paused the game and in one go, did a series of channels down that one single square all the way down to the water. I figured the dwarf would do the row of holes from up all the way down, and fall to the water one floor down, swimming out (the place was one square away from shore)
This all seemed like a good idea at the time.
I unpaused and focused on something completely else. Suddenly I get a message "Rimtar Damngoodblacksmith is too injured to continue digging" (or close to that). What the Armok? I check combat reports. "Gabbro hits Rimtar to the head, breaking his spine etc." "Spinning Gabbro attacks Rimtar and hits him in the neck, severing a motor nerve" etc.
I go to the dining hall - there's no hole there below the first one I made, just the channel placemarkers. I go down z-levels. I find out that in three occasions, the chute downwards is next to a mining tunnel. From the topmost of these, the dwarves have, apparently, started channeling down. I go down more z-levels, and lo and behold, Rimtar and another dwarf are unconscious / dead / paralyzed all the way down in the cavern river. No one saves them and they die.
Moving up to the dining hall, another dwarf has started channeling, finally from the top. I know I should stop this, but with morbid curiousity I watch as he digs and digs down, eventually reaches the floor from where the other dwarves started - and promptly plummets down the chute to his doom at the bottom of the river and dies.
I am not sure what exactly went wrong. Is it plausible, that since the channel places were reachable from mining tunnels below in three spots, that one dwarf dug one channel in one of these tunnels and worked his or her way down, and when Rimtar and the other guy started from above, they eventually hit an empty floor and plummeted down, as happened to the dwarf who started from up? Or something else?
How should I have done this without fatalities?
At least it was a very interesting moment and added some deaths to my memorial hall that weren't "fetal position from dehydration" or by being killed by vampires.