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 pursuant to the budget appropriations. The Commission 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 reappropriated during the next fiscal year.