What do you call concrete structures protecting beaches?

Solution 1:

As far as I recall there is no one unified name for concrete structures that are protecting the beach, each of the terms you have given has their own usages, in different contexts.

For example:
Sea wall: is basically used to refer to walls of concrete that are created to counter high waves and reduce the impact of a Tsunami by being the first line of defence.
E.g. Japanese Sea Wall

Meanwhile, a wharf, quay, or staith is a structure on the shore of a harbour where ships may dock to load and unload cargo or passengers. It has facilities for handling the ship, and it is generally not made with the intent of protecting beaches.