I think Dwarven one-step-at-a-time thought processes must be contagious. Last evening I had a wonderful idea. The fortress I am working with at the moment has a brook that falls five levels through a notch in the landscape. It is also fed by some aquifers that are cut by that notch, so there is "muddy brook (7/7)" on top of the "brook (7/7)" in the lower section. The layers in between have the occasional 1/7 or 2/7 next to the face of the waterfall cliff due to the gel-like properties of DF water. There was lots of mist in that little (four tiles wide) canyon. I cut out a circular room halfway down, centered on the canyon. It is about 28 tiles across. I floored most of the canyon gap and did the part closest to the waterfall cliff-face with alternating grates and floor, and left an open gap right next to the cliff-face for the gel to ooze down. Mist was coming both from the waterfall above the floor and from the turbulant water below the floor.
I put a statue on the far side from the entrance from the delvings, and made the entire room a statue garden. The Dwarves loved it. Lots of room to socialize, some overhead light so they did not get cave-adapted (their previous gathering place was 8x8 near the outdoor gardens), and a waterfall on one edge. Pleased with myself, I went to bed.
This morning I began playing again. The first wake-up call was a goblin seige that looked down into this canyon and said "Hey guys! Fish in a barrel!" I only lost one dog to that, mostly because the goblins got more interested in the fact that some of them had been impaled at the gate.
After the seige, I set my masons to walling off the access to the top of the canyon. Everything looked rosy again. Then winter arrived. Dwarfsicles! I actually only lost one child but, because the ice hides the bodies, I was not able to tell where she had been standing. However, I saw that some of the tiles now covered with solid ice were ones that only had 1/7 water on them part of the time and the rest of the time only mist.
Panicking, I immediately set the Dwarves to removing the grates and the flooring in the icy area. I guess I don't panic quickly enough, or else I had spent too long looking for the body of the frozen child. At any rate, the ice thawed and two idiot Dwarves, who did not understand that unconnected grates don't support Dwarves, pulled the supports out from under another two dwarves who fell into the now melted "muddy brook (7/7)". I did manage to get them out, along with various dogs and horses, and have now walled off the waterfall from the meeting area.
Oh well, at least now they are not trampling the aboveground crops on their way to their statue garden.