Brute I've been researching the same issue as you. I have an area that floods out easily (water recedes fairly fast) and is generally just damp and low-lying. A lot of my reading is saying brassicas like purple top turnips along with oats and wheat. I can't say that I have personal experience to prove it works, but it seems like a lot of guys saying you can get turnips to grow in really damp or wet soil with the right pH.