I decided to try a fortress design based on someone's post about using every other layer for plumbing. So far my implementation has not been brilliant, but I've had no floods. My previous (and first) 0.31.08 fortress was an experiment in using burrows to define clan quarters. My clans in that fortress were defined by religion. In this fortress I have reverted to clans defined by productive marriages between immigrants, ie, a wedded immigrant couple is not assigned quarters until they have produced a child in the fortress (children who immigrate don't count). So far I am up to 19 clans, which is why I was using religions last time. I think I am getting the hang of burrows, though. I have one bedroom assigned to the founding couple, and a dining room with four tables and four chairs which has no owner but because it is inside the burrow can only be used by clan members (which at this point are the parents and their children). It is not as nice as one huge common dining hall decorated with engravings but they do use it and they seem happy ("dined in a great dining room lately"). When I get some more beds made, I will make build beds for the children and perhaps assign them, or perhaps not. I am also trying out some pit trap/weapon trap/cage trap defensive ideas, which I will eventually test by turning invasions on. I am not sure how to house the childless couples and singletons. At the moment they have a public dormatory, but no dining room at all. I may have to define a YDAA (Young Dwarf's Armok Association) for those Dwarves. In this fortress there are no aboveground farms. Not only that, but the seeds of any aboveground crops which are either harvested or bought, and then brewed or processed, are cooked and eaten (or sold, as they are not very tasty). No aboveground farming allowed this time.
I have only dug 9 levels under the ground so far, this time.