For purposes of the Riverfront Development District Act:
(1) Authority means a riverfront development authority established in accordance with section 19-5305;
(2) City means a city of the metropolitan, primary, first, or second class;
(3) District means a riverfront development district established in accordance with section 19-5304; and
(4) River means the Missouri River, Platte River, North Platte River, South Platte River, Republican River, Niobrara River, Loup River, North Loup River, Middle Loup River, South Loup River, Elkhorn River, North Fork of the Elkhorn River, or Big Blue River.