The appropriations made by the budget ordinance for debt service and other fixed charges shall become available for expenditure upon the filing of the certified copy thereof with the Director of Finance. Appropriations for capital improvements shall become available as Council shall provide by Ordinance. Appropriations for current operations shall become available for encumbrance only when approved by the City Manager as being in conformity with the budget appropriations. Any unencumbered balance of any appropriation item shall lapse at the end of the budget year. Upon a showing of necessity by the City Manager, Council may reduce or revise appropriations during the course of the fiscal year or make transfers.