From the effective date of the budget, the several amounts stated therein as proposed expenditures shall be and become appropriated to the several objects and purposes named therein. Except as provided in this Article, no funds of the City shall be expended, nor shall any obligation for the expenditure of money be incurred, except pursuant to the annual appropriation ordinance provided by this Article. At the close of the each fiscal year any unencumbered balance of an appropriation shall revert to the fund from which appropriated and become available for reappropriation for the next fiscal year. The City Council may transfer any unencumbered appropriation balance or portion thereof from one office, department, or agency to another, at any time. The City Manager shall have authority, without City Council approval, to transfer appropriation balances from one expenditure account to another within a single office, department, or agency of the City.