The user charge system shall generate adequate annual revenues to pay the costs of annual operation and maintenance of the sewage works, replacement fund, and pay portion of costs of annual debt retirement of bonded capital improvements of sewage works which the city may by ordinance designate to be paid for by the user charge system. That portion of the total user charge which is designated for operation and maintenance of the sewage works and replacement fund shall be established by this chapter. [Ord. 374 § 2, 1982; Code 1975 § 3-3.0504.]