Ironically, I have the opposite situation. Where I am in our marina, the depth is 7 metres under the boat - they dredged our section out really well - other areas not so deep, but deep enough. Actually, Moreton Bay being what it is, on a common trip out, unless we head up to the more northern and open parts of the bay, our berth is the deepest sounding we see.
At least if you drop something valuable overboard at the berth, you have a reasonable chance of recovery. When I dropped my bow roller assembly, (yeah….forgot to tie a line to it - I was "just seeing how it looked" - it slipped, bounced off the dock, and you guessed it), it cost me two cartons of beer to a nearby berth-holder with scuba gear to retrieve it.