Approval of the preliminary plat by the Council does not constitute approval of the subdivision but is merely an authorization to the subdivider to proceed with the preparation of the final plat. Specifications and engineering construction drawings, including profiles, cross sections and details applicable, of all public improvements, including streets and alleys, water systems, sanitary sewerage systems and storm drainage, shall be in accordance with preliminary plat and shall be submitted to the Engineer not less than seven days prior to the commencement of any construction. A maintenance bond guaranteeing all improvements for a period of four years from the time of city acceptance, against defective materials in workmanship, shall be provided before construction is undertaken.