Hey JK...
Let's get outta this box, eh?
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What if....
You set the pier on permanent concrete footers in the shallows that are accessible by equipment. Then, build a hinged section that attaches to the end of the last permanent section. Attach the other end of this hinged dock section (with another set of hinges) to a floating dock. It will always be at the perfect height. The drawback will be if/when you get a hard freeze. I don't know how much abuse the various floatation units will take, let alone the shear of moving ice floes.
