The City Manager may prescribe such general rules and regulations as he may deem necessary or expedient for the general conduct of the administrative departments and the care, control and use of all City property, provided such rules and regulations are not inconsistent with the Charter and City ordinances. The head of each department shall in like manner prescribe such rules and regulations as he may deem necessary and expedient for the proper conduct of his department, not inconsistent with rules and regulations prescribed by the City Manager.