Iowa Code § 468.634
Upon receipt of a petition, signed by the owners of the lands served by a mutual drain, requesting that such drain be combined with an established drainage district, the board shall hold a hearing with due notice to the owners of all lands affected by said mutual drain, and if the board finds it desirable it may by resolution make such mutual drains a part of the established district. Such hearing and resolution may be continued as the board deems necessary for the collection of additional information as provided in section 468.633. Such combination with an established district shall constitute dissolution of the mutual drain, and shall be so recorded, after which such mutual drain shall be a part of the district drain in all respects.
Iowa Code § 468.634
89 Acts, ch 126, §2