Sligh1, you can actually look at alfalfa. I was in a forage meeting all day and learned alot about different types of forages.
There is a aqua alfalfa that has been around a year or two. It really doens't grow in water, just the name they came up with for it being very tolerant of "wet feet" and very poor drained soils. From all of the info that I have on it, it can withstand a flood or two, as long as the water doesn't sit on it for a week or two. PM me if you are interested in more information on it. I can email you the literature that I have on it.