Appropriations for current operation of the organization units of the city government shall become available for encumbrance only when allotted by the city manager, based on currently valid work plans for each agency made in conformity with the appropriation ordinance and submitted to the city manager by the agency head at least five days before the end of each calendar quarter for the succeeding calendar quarter. The allotments made by the city manager shall be filed with the director of finance on or before the first day of the quarter to which they relate and shall authorize the director of finance to accept, from the organization units involved, purchase orders, contracts and payrolls for encumbrance, and payment to an aggregate amount not exceeding the quarterly allotment for each item. The total annual allotment to any agency may not exceed the total amount appropriated for the use of such agency during the fiscal year. Any unallotted balance of any appropriation item and any unencumbered balance of any allotment at the end of the fiscal year shall be lapsed into the municipal treasury.