Iowa Code § 468.5: Location across railroad.

When any such ditch or drain crosses any railroad right-of-way, it shall when practicable be located at the place of the natural waterway across such right-of-way, unless said railroad company shall have provided another place in the construction of the roadbed for the flow of the water; and if located at the place provided by the railroad company, such company shall be estopped from afterwards objecting to such location on the ground that it is not at the place of the natural waterway.