Anyone know about pouring concrete footings w/ high groundwater table?

I think your over thinking it. Its a chicken run, just dig your holes drop your post in and pour your concrete dry from the bag.

Pat, I have done this with very large, elevated decks before, and it can be done safely. Wrap the sonotube in 8 mil plastic and duct tape it around the top that sticks above soil grade. If you use 9' wide plastic, you will have enough to completely encase up to a 48' sonotube.

Dig your holes and add about 4" gravel in the bottom of the tube. The plastic will keep the water out long enough for your sakrete to set. Once it's set, if moisture does get in, it will only help to cure your concrete harder.

The plastic will keep the ground water from rushing in to the sonotube, but be prepared to have your gravel and concrete ready as the hole is dug, otherwise you will float the tube out of the hole.

I have had 16'x60' decks, elevated 12' off the ground standing for over 20 years using this method with no sinking. Have had to do this many times when building around natural springs and high water tables.

Let me know if you have other questions about it and good luck to ya. Post pictures when you get foing please.