Iowa Code § 468.4: General rule for location.

The levees, ditches, or drains herein provided for shall, so far as practicable, be surveyed and located along the general course of the natural streams and watercourses or in the general course of natural drainage of the lands of said district; but where it will be more economical or practicable such ditch or drain need not follow the course of such natural streams, watercourses, or course of natural drainage, but may straighten, shorten, or change the course of any natural stream, watercourse, or general course of drainage.