Utah Code § 17-8-5.5
The county legislative body may also provide by ordinance for the protection and use of flood channels and present flood plains on rivers, streams, and canals located within the county and the incorporated municipalities in the county and may establish by ordinance the boundaries of these flood channels and present flood plains. The county may acquire and hold by gift or purchase, such lands, rights of way, easements, or other interests in property within the established boundaries of these flood channels and present flood plains. Flood plain as used herein means the lands along the course of the river or stream which is periodically flooded and for which flood control protective works would normally be provided or desirable.
Utah Code § 17-8-5.5