Desert embark. I need a lot of water for a project near the surface and the oasis I've built my fort around can't provide that much.
Luckily I have hit the caverns!
Cavern 1 has water, but it is rather inconveniently placed in an out-of-the way map corner.
Cavern 3's lake is in a nice spot, but ever since the venomous undulating glass frog incident I've been wary about doing anything on that layer.
Cavern 2's water is directly underneath my fort, making it an ideal source. So that's where I set up my pumpstack. Lots of pumps.
So my pumps start working and the cistern starts filling...
Goblin siege!
I hotkey to the surface and start ordering civvies to their emergency shelters, get the militia in position, double-check if the marksdwarves actually picked up their ammo for a change and then went about opening trap corridors to whittle the goblin numbers down...you know, normal stuff.
By now most of you probably realize what happened.
For those who didn't, here's a helpful hint:
When you turn a pumpstack on, make sure you do not forget to turn it off again. 4 dead dorfs, one more who'll probably be leaving us soon due to alternating periods of depression and random violence...and mud all over the floors of three levels, including the main dorms and the primary stockpile. There's trees growing everywhere.
At least some of them are tower-caps...