Bay 12 Games Forum

Early in my current fort I accidentally flooded it due to being new and not having an understanding of the water pressure mechanics at the time, as a result I had to build a tunnel down to the first caverns to drain the water into, now, several dorf years later the river is noticeably draining, is there anyway I can block off the drainage tunnel to stop the caves from filling up and keep the river up. This problem's also caused the water pressure in some other things to be lower, should I just pump water back up from the caves or is there another way to stop the water flowing from the river into the caves?
Edit: And yes I was stupid/forgetful enough not to put a master floodgate at the first point where the river water comes into the fortress.

I'm relatively new to the game but understand most of the mechanics fairly well (I think). But when I'm under siege by goblins and I station my troops so as to force the goblins through trap ridden corridors to capture/kill as many as possible without my dwarves getting harmed some of my military dwarves simply walk all the way out of the fortress and try to kill the goblins themselves, this usually results in death unless the dwarves in question are some of my higher level military dwarves, how do I keep them closer to their station and stop the unnecessary deaths?
And secondly I've recently built a 19 z-level death pit yet all the goblins and most of the animals that I've thrown into it have survived and sometimes not taken any damage at all, does the pit simply need to be deeper or is there something more to it?
And finally this is my first post on the forums, so apologies for any idiocy or failure to understand basic game mechanics and/or the workings of the forum, thanks for any help!