The council may establish a separate fund to be known as the "Contingent Fund". The unspent balance remaining in the contingent fund at the end of each year shall be left in the fund; the difference between the balance at the year end and the amount needed for the next ensuing year shall be obtained from general taxes each year. Contingent fund monies cannot be spent without the express approval of council, and upon recommendation of the city manager, and such monies may only be spent for expenditures which could not have been readily foreseen at the time of budget preparation.