There is hereby vested in the State Docks Department power of eminent domain in carrying out the provisions of this article, which power shall apply not only as to all property of private persons and corporations, except as limited in Section 33-2-3, but also as to property already devoted to public use; provided, that the State Docks Department shall have no authority to acquire without consent of the owner thereof by condemnation any property now operated and used for port purposes or such purposes as the State Docks Department is authorized to acquire and use property for, unless the necessity therefor be alleged and proved.