Iowa Code § 468.80: Funding or refunding indebtedness.

Drainage districts may settle, adjust, renew, or extend the time of payment of the legal indebtedness they may have, or any part thereof, in the sum of one thousand dollars or upwards, whether evidenced by bonds, warrants, certificates, or judgments, and may fund or refund the same and issue bonds therefor in the manner provided in section 468.367.