(a)   Except for purposes which are to be financed by the issuance of bonds or by special assessment or for other purposes not chargeable to a budget appropriation, no money shall be drawn from the treasury of the city except in accordance with an appropriation thereof for such specific purposes, nor shall any obligation for the expenditure of money be incurred without an appropriation covering all payments which will be due under such obligation in the current fiscal year.  The council, by resolution, may transfer any unencumbered appropriation balance, or any portion thereof, from one account, department, fund or agency to another.
   (b)   The council may make additional appropriations during the fiscal year for unanticipated expenditures required by the city, but such additional appropriations shall not exceed the amount by which actual and anticipated revenues of the year are exceeding the revenues as estimated in the budget, unless the appropriations are necessary to relieve an emergency endangering the public health, peace or safety.
   (c)   Except in those cases where there is no other logical account to which expenditures can be charged, expenditures shall not be charged directly to the contingency fund (or other similar fund).  Instead, the necessary part of the appropriation from the contingency fund (or other similar fund) shall be transferred to the logical account, and the expenditure charged to such account.
   (d)   At the beginning of each quarterly period during the fiscal year, and more often if required by the council, the city manager shall submit to the council data showing the relation between the estimated and actual revenues and expenditures to date; and if it shall appear that the revenues are less than anticipated, the council may reduce appropriations except amounts required for debt and interest charges, to such a degree as may be necessary to keep expenditures within the revenues.
   (e)   The balance in any budget appropriation which has not been encumbered at the end of the fiscal year shall, subject to restrictions imposed or permitted by law, revert to the general fund.