The city is authorized to issue bonds in an aggregate principal amount not to exceed twenty million dollars and to issue such bonds, from time to time, in such series and amounts as are determined by the council to be necessary or appropriate to provide for the costs of facilities approved by the council. Bonds shall be negotiable instruments for all purposes, subject only to the provisions of such bonds for registration. (Ord. 1520 NCS §1 (part), 1982.)