Iowa Code § 468.357
After the establishment of a drainage district, including a pumping plant, and before the completion of the improvement therein, the board or boards may, if deemed necessary to fully accomplish the purposes of said improvement, by resolution authorize the establishment and maintenance of such additional pumping station or stations as the engineer may recommend, and if a petition is filed by one-third of the owners of land within such district asking the establishment of such pumping plant or plants, the board or boards must direct the engineer to investigate the advisability of the establishment thereof and upon the report of said engineer the board or boards shall determine whether such additional pumping plant or plants shall be established.
Iowa Code § 468.357
89 Acts, ch 126, §2