Neb. Rev. Stat. §§ 39-1818
A water impoundment structure which will result in temporary storage and flowage of water upon, across, or adjacent to a road upstream from such structure may be approved only if such road would not be inundated because of the storage in such structure of waters from a ten-year, twenty-four-hour or lesser frequency storm. A water impoundment structure which will also serve as a roadbed may be approved and constructed only if the structure would contain the runoff from a twenty-five-year, twenty-four-hour frequency storm without water overtopping such structure or being discharged through its emergency spillway, except that if the road which is subject to such inundation is classified as a local road or remote residential road with current average daily traffic of fifty vehicles or less, the containment of a ten-year, twenty-four-hour frequency storm shall be sufficient. In making the storm frequency determinations required by this section, any recognized method may be used.
Neb. Rev. Stat. §§ 39-1818