No work shall be done by the city until the estimates of the engineer have been filed with the city clerk. The work may be done by the city by day labor or by contract. No contract shall be entered into for an amount exceeding the estimate of the engineer. If the work is done by contract, the contract shall be let upon competitive bids after not less than five (5) days' published notice. The work shall be done under the supervision of the overseer of streets and the city engineer. (Prior code § 9-1-10)