Whenever any new work, repairs or improvements in the streets, bridges, sewers, culverts, alleys or public places within the city limits are contemplated, and before any such work is begun, the city engineer shall formulate plans and specifications therefor and shall submit the same, together with an estimate of the cost thereof, to the board of aldermen. When such work is authorized, it shall be carried into effect under the direction of the city engineer. The city engineer shall carefully preserve the plans, estimates and specifications for any and all public work executed, also the plans, estimates, etc., of all proposed public work that may be in contemplation, or shall have been proposed and rejected, and keep them on file for ready reference. (Code 1953, § 2.19)