At the close of each fiscal year, the unencumbered balance of each appropriation shall revert to the fund from which it was appropriated, and shall be subject to future appropriation. Any accumulated revenue not appropriated as hereinbefore provided, and any balances at any time remaining after the purposes of the appropriation shall have been satisfied or abandoned, may from time to time be appropriated by the Council to such uses as will not conflict with any uses for which such revenues specifically accrue. 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 appropriations made by the Council.