If the Director of Public Works, for any reason whatsoever, may not perform any of the duties or functions by this Article imposed upon him, or if it becomes inconvenient for him to perform any such duties or functions, then, in every such case, such duties and functions may be performed by the City Engineer in said Department of Public Works, as a substitute for said Director, or, in any such case, said duties and functions may be performed by anyone in said Department designated by the Chief Administrative Officer of said City and County. The duties and functions hereby imposed upon said City Engineer may be performed by anyone else in said Department designated by said Director. Whenever such a substitute shall act, either for said Director or for said City Engineer, the records of said Department shall include a written designation by said Chief Administrative Officer or said Director, as the case may be, appointing such substitute. Such designation shall indicate the period during which such substitute shall be authorized so to act. Such written designation shall be conclusive of all facts therein recited, and all acts of such substitutes, respectively, shall have the same validity as if they had been performed by said Director or said City Engineer, as the case may be.