After the budget has been adopted, no money shall be drawn from the Treasury of the City nor shall any obligation for the expenditure of money be incurred except in accordance with the budget appropriation. The Council may transfer any unencumbered appropriation balance or any portion thereof from one department fund or agency to another. The balance in any appropriation which has not been encumbered at the end of the fiscal year shall revert to the General Fund and be re-appropriated during the next fiscal year.