I'd heading back to the corduroy idea.
It was suggested that I lay the logs down and then cover them with stone from nearby stone walls (of which I have plenty).
That way, even if the logs submerge, they'll provide a platform for the rock (so they don't disappear in the muck), and the rocks won't cost anything to buy or transport back there.
Lots of manual labor though. A machine with loader would help -- don't think I could get the mrs. to agree to a tractor at this point (though I'd love one). I guy offered to sell me a Kubota
L3130 with loader on the front (only owner, well maintained) for $10k. It's very tempting. But, I'm not sure it'd be good for this kind of work anyway.