Payrolls shall be submitted to the City Manager for approval, when prepared by the City Auditor, and upon the City Manager’s approval thereof, the City Auditor shall issue his or her warrants in payment thereof when due. It shall not be necessary for the City Auditor to encumber in advance or to certify as to the availability of funds appropriated for personal services except those obtained on a contractual basis, provided that upon issuance of such warrants the City Auditor shall immediately cause the appropriate funds to be encumbered to the extent of the warrants issued.