Iowa Code § 468.540: Refunding bonds.

The board of supervisors of any county may extend the time of the payment of any of its outstanding drainage bonds issued in anticipation of the collection of drainage assessments levied upon property within a drainage district, and may extend the time of payment of any unpaid assessment, or any installment or installments thereof. The board may renew or extend the time of payment of such legal bonded indebtedness, or any part thereof, for account of such drainage district, and may refund the same and issue drainage refunding bonds therefor subject to the limitation and in the manner provided in this part.