Refunding bonds for the purposes set out in this part may be issued to pay off and take up bonds issued in payment for drainage improvements under prior laws or to refund any part thereof. Bonds thus issued shall substantially conform to the provisions of the law relating to drainage bonds and the face amount thereof shall be limited to the amount of the unpaid assessments, with interest thereon, applicable to the payment of the bonds so taken up.
89 Acts, ch 126, §2
CS89, §468.375