The reason this megaproject idea was unnecessary, and stupid, is not necessarily that the idea was flawed, but that I attempted it on a completely unreasonably large scale. And that it did not involve magma.
So I got this idea to drain a lake (a big lake) and pump it into a giant cistern suspended in the air over the lakebed. Invaders would have to come into the lakebed to get to the fort, and I planned to drop the entire lake on top of them when they did.
First, I had to drain the lake. I figured out how to use floodgates to shut off the rivers feeding into the lake (see my post "water dam" on the DF map archive). As for the lake itself, rather than build the overhead cistern and pump the water up to it, I decided to build a secondary cistern underneath the lake and drain down into that first. So I'd actually have two reservoirs: the top one for dumping water into the lake, and the bottom one for quickly draining the lake in case I needed to let in a caravan or something. A pump stack would take water from the bottom reservoir back to the top reservoir to reset the trap.
So I dug out this absolutely enormous cubic volume under the lake, something like 100x100x13. And that's when I hit the first problem: the huge number of stones killed my framerate. I decided to dig out another floor and drop it on the stones to destroy them. Unfortunately, this just made more stone. I had misread the wiki and thought floors destroyed items, but actually that requires dropping walls on things.
Digging out such a huge area uncovered lots of gems, resulting in a legendary gem cutter and a large created wealth disproportionate to the rather small population of my efficient work crew. This attracted notice by the local goblin nation...
Throughout multiple seiges, I managed to get almost, but not quite, to the point where I would drain the lake. I had to build the pump house at the bottom of the cistern first, because I would not be able to access it again after the cistern was full of water. Anyhow a final, large goblin seige came and decimated everyone just before it was completed, except for my mayor and the human liaison. I didn't want my human liaison to die because I didn't think if he'd be replaced even if I reclaimed. I discovered that since the liaison was trying to meet with my mayor he'd follow him anywhere, so I drafted the mayor and sent him to the only place the goblins hadn't yet overrun: the cistern.
There was actually one other dwarf who managed to survive on the surface for a short time while the mayor was leading the liaison down into the cistern. I ordered that dwarf to operate a special pump that took water out of the lake and flooded just the access corridors to the cistern, right on the heels of the mayor, so that it would be impossible for the goblins to follow him. (The fact that I happened to have a pump that specifically floods the workers' access shaft is not due to foresight, but merely hints at the depths of ridiculosity that arise by patchwork fixes of logistical planning errors...) Anyhow that dwarf died valiantly operating the pump. The pump was left "on" (in the "start pumping") state. This will become important later.
The mayor and liaison were now safely sealed in the cistern, specifically on the narrow catwalk running along the top of the cistern overlooking a 14 Z drop and room of mind boggling empty volume. Not to worry, the mayor was also a miner and was still carrying his pick. I would dig a secondary tunnel up to the main encampment and undermine the food stockpile to safely drop barrels of food and booze out from under the goblin's noses. I would carry on the megaproject alone, solitary survivor of a mad obsession, and finish the pump house and drain the lake with one dwarf if I had to.
Unfortunately, the mayor was stuck in the "attend meeting" bug. He wouldn't dig, he wouldn't build bridges, he wouldn't do anything except "attend meeting" with the liaison - but the liaison is right there, and he's not meeting with him. Drafting, undrafting, job orders, cancel, it didn't matter. There's not much you can do in Dwarf Mode when you don't have anyone who will obey your orders. So I had to abandon the fortress.
On reclaim I came back to find the mayor and liaison had somehow gotten back to the surface and made buddy-buddy with the goblins too, who were now friendly. The human liaison must have been scared completely out of his mind by the whole ordeal, because now he just stands at the side of the lake and stares off into space. So much for preserving trade agreements with the humans. It would have been more humane to let a goblin arrow take him.
I decided to finish the work and popped down below for a look. O... M... G... Whereas the cistern had been empty when I abandoned, it was now full of water. Now instead of just getting rid of the water in the lake (the lake was still full), I had to figure out how to get rid of the water in the cistern too!
What happened? Well let's examine the facts:
1. A pump that takes water from the lake and floods (a portion of) the cistern was left on.
2. The mayor made it to the surface somehow during the time the fortress was abandoned
3. The mayor also had the pump operating labor on.
Imagine, if you will, years of fortress time passing while I, the player, am absent, during which the mayor has no mission except to operate this pump that puts lakewater into a cistern while rain refills the lake behind him...
To fix this, I built eight atom smashers in a room adjacent to the bottom of the cistern, connected the atom smashers all to a repeater, and waited years of fortress time for all the water to be atom smashed. During this time I kept mysteriously losing dwarves. For the longest time I couldn't figure it out but what was going on was no matter how many doors I installed and forbid, the little buggers would find some way to path under the atom smashers. There was some pile of picks or socks or little pieces of gear that was on the far side of the gauntlet of eight atom smashers, and if someone miraculously managed to do a Mr. Magoo walk between all of them, he would certainly be caught on his return trip. So I lost about a dozen dwarves but eventually all the water was let out of the cistern and smashed.
Finally, the big day had arrived: everything was finished. I instructed a miner to dig the ramp that would drain the lake! Clink! Clink! Clink! At last the stone gave way, allowing the water to come rushing past, and...
My computer froze. Minutes passed. A frame. Then, another frame.
I left the computer on for 24 hours straight, and the cistern is only half full, with a wall of water falling at a diagonal. And that, my friends, is why this is the least necessary/stupidest megaproject ever: because even if I finish it, this is how long it's going to take every time I spring that trap.
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Topic: What was your least necessary\stupidest megaproject ever? (Read 3168 times)