a.   If the City Manager certifies during the fiscal year that there are available revenues in excess of those estimated in the budget, the Council by ordinance may make supplemental appropriations up to the amount of such excess revenues.
   b.   If it appears probable to the City Manager during the fiscal year that the revenues available will be insufficient to meet the amounts appropriated, the City Manager shall report to the Council without delay, indicating the estimated amount of the deficit, any remedial action taken, and recommendations as to other possible steps.  The Council shall then take such further action as it may deem necessary to prevent any deficit, and for that purpose it may reduce by ordinance one or more appropriations. 
   c.   At any time during the fiscal year, the City Manager may transfer part or all of any unencumbered appropriation balance among programs within a department, office or agency.  Upon written request by the City Manager, the Council may transfer by ordinance part or all of any unencumbered appropriations balance from one department, office or agency to another.
   d.   No appropriation for debt service may be reduced or transferred, and no appropriation may be reduced below any amount required by law to be appropriated or by more than the amount of the unencumbered balance thereof.  The supplemental and emergency appropriations, and the reduction or transfer of appropriations authorized by this section, may be made effective immediately upon adoption.