Maybe I'm just dense, but I can't seem to imagine how putting an anchor and chain/cable out in the water attached to the pond end of the dock allows for high and low tide (so to speak). If the chain is loose enough to allow for high water then it's not doing anything at normal level (it's too loose). If the chain is tight at normal level, the dock has to pick up the anchors or be submerged when the level rises to the emergency overflow and the anchors hold it down.

What am I missing here?

Now, I could attach to the corners of the first cross walk with chain or cable and anchor them to the bank at the same elevation as the hinge...this would allow for the dock to rise and fall but still resist the side to side forces. This option is a little unattractive to the eye, but would work.

I hope to convince myself that the hinge can be made stout enough to do this job by itself. It is made of 2-1/2" OD, 3/16" wall tubing and 1/4" plate and 1/4" angle iron. It's my ability to construct the concrete foundation that I'm fuzzy on.

Fish on!,
Noel