The city council of any city of the metropolitan class shall have concurrent jurisdiction with the county board of any county having a population of two hundred thousand inhabitants or more, and the power to cause all natural watercourses, as defined in section 31-228, which are within its corporate limits or within three miles thereof, to be kept clean and free of obstructions in such manner as to permit the natural flow thereof.
Neb. Rev. Stat. §§ 31-227