Appropriations may be made pursuant to this chapter for the following purposes:
(a) To reduce special assessments and special assessment bonds levied and issued against real property fronting upon the public improvement or in the district estimated to have been benefited thereby.
(b) For the payment of any portion of the principal or interest of, or for the purchase and redemption at a discount of, or the transfer to the interest and sinking fund for the discharge and payment of bonds, the proceeds of which have been used for the acquisition of rights of way or easements for, or for the construction, maintenance, improvement, or repair of streets, bridges, or culverts within the city.