No I doubt very much the flooding has killed them.. Turkeys can fly and will head up into the trees if the need arrises. I think they all headed up to higher ground. There is no need for them to hang around the streams or rivers if there has been a lot of rain or snow melt. They will surely find water pockets up on the higher ground to drink from. So I would start checking the ridges more or farther back from the areas of flooding..