Since the death of my last fortress, I started another fortress in the forest for a different experience.
Being in the middle of a forest, you build your fortress down instead of into the side of a mountain. I picked a spot near a river, and quickly built three large farm plots for different plants. My grower quickly went to work tilling the soil (rock must be wet to grow on, but soil or sand works fine if near a river), and quickly began planting. I struggled with fortress design since I was no longer building from left to right, but settled on having most stockpiles above ground, and cutting the corners out of my dividing walls to make it easy to get around the fortress quickly. After most of the digging was done, I got my miner working on connecting the many lakes in the area to the river, to make a moat for the fortress (though there weren't really any nearby threats). All the while, I was building barrels, and constantly brewing plants, which generated plenty of seeds, and kept the food and drink development working brilliantly well.
After the moat was complete, I sent the miner down to the bedrock, and had him dig patterns to reveal any veins of precious or useful metals. I returned to the workshop development, and consulted the dwarf fortress wiki to find out how to make the clothing that the trader said they needed next year. A few missteps later, I was making pants from the pig tail plants I was growing. Sweet! I've never made clothing before! Around now the elven traders arrived, and demanded I have a trade depot, which I was happy to build. But for some reason, my carpenter was selected to trade instead of my trader, and he didn't know the values of the items. After a few attempted trades, the elves were becoming testy, and began acting like douche bags. This would not do. I ordered walls built around the trade depot, and screw pump parts, and floodgates built. I surrounded the trade depot with walls, and floodgates on one side controlled by a lever. Then I devised a method of pumping water from the nearby river up a few levels, and then how to dump it into the trade depot to drown snarky traders, and "acquire" their goods. Of course, once I started planning, I wanted to make it perfect, and the traders left long before I was done, but when I finally got the waterworks figured out, I skipped down a level to check on my fortress, and found it in the middle stages of flooding.
In my haste for good waterworks I dug out a corner of one of my farm plots very near the river, and it began flooding as I worked on my sophisticated trade depot trap. Genius.
I quickly ordered everyone to ground level, except my legendary miner who could swim, and got him building retaining walls (which was difficult because you can only build in one level of water, and it was spreading fast), but wasn't able to keep up. The cut-out corners, and many shortcuts that made my fortress efficient, were also making it very hard to segment off the water. Within minutes, I lost almost all of the fortress, and stranded three dwarves who couldn't make it around the rising waters.
I quickly modified the pump, and powered it up to buy myself enough time to build a retaining wall at the source of the leak, but I couldn't work it out. Due to the liquid dynamics, and the fact that the water level was so high on both sides of the leak, any attempt to approach the leak would result in widening the leak, and I wouldn't be able to get another pump working on the approaching area. Logistically, I couldn't stop the leak. The game mechanics made it almost impossible. After a while of trying anyways, I gave up, knowing I would restore to another save I had backed up for fear of save file corruption.
I watched the water level raise, and noticed a few things. First, the water was taking longer to get through the door to a bedroom one dwarf was trapped in, this made sense, because the door is an obstruction. I might have had time to save my fortress had I just used more doors in those cut-corners that connected my fortress so well. Secondly, the dog in the same room as the dwarf drowned before the dwarf did. After thinking about this a little bit; this made sense because the dog was closer to the ground than the dwarf. Just another reminder that it's the little details that makes this game different from all the others.
Just as my dwarves began getting hungry, and thirsty (all the food and drink stores were underwater) I quit, and restored to the save which was literally two steps from digging out that fateful section of ground. Lucky, I guess. I continued playing, knowing my dwarves were living on borrowed time, and completed the trade depot flood machine. I then dug a wider moat, and built a draw bridge out of some purple stone I found in the bedrock. The first year passed quickly, and I eagerly await migrants.