The difference between wharfage and dockage

There is not much difference. "American Heritage Dictionary [Double Interpretation]" wharf: A landing place or pier where ships may tie up and load or unload. Pier: A landing place or pier where ships can berth and load or unload cargo.

dock: A pier; a wharf. Pier; berth.

Often used as docks: a group of docks in a commercial port used for ships to dock.