Is it now. You have measurements showing the tidally averaged depth hasn't changed an inch? Note: I am, of course, assuming you have a pier, not a dock. A dock generally is on floats for small craft, and automatically adjusts, so I assume you mean a pier, which is not floating?
Here, if it is attached to your personal property and it does not float, it is called a dock (whether it is on a pond, lake, river or salt water creek). Many of what we call docks have a smaller part (either at the end, like mine or along one side or the other that is called a "floating dock" by us). If it is big enough to have a building on it (such as a restaurant or club) or for something big, like ships, then it is called a pier.
So, using the semantics that are in common use here. My dock, which has a floating dock at the end because there are 4 ft to 7.5 ft normal tides twice a day (the amount depends on the moon, the wind, the rain and some other factors). So, when standing on my floating dock, there is an average water line from silt in the water that can be viewed on the supporting poles. Naturally we clean the supporting poles from time to time. And measurements are taken to see if any poles need to be replaced, if the dock is tilting in some manner or what have you. Over the years those measurements do vary an inch or so up or down from the other years of the high and low watermarks on the poles. But over the years since we built the dock (1964 to now), both the high waterline and the low waterline has stayed in their respective three inch zones.
