Whenever the Council determines that it is necessary to borrow money under M.S. Chapter 429, as it may be amended from time to time, for the financing of any local improvement the cost of which is to be paid in whole or in part from special assessments, the borrowing shall be affected by the issuance of improvement bonds of the city under that chapter, for the payment of which bonds and interest thereon the full faith and credit of the city shall be irrevocably pledged.
(’77 Code, § 303.13)