Upper Avon vs River Avon

Upper Avon and River Avon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Upper Avon	Yes	No	No	No
River Avon	Yes	No	No	No

As nouns, Upper Avon and River Avon are synonyms defined as:

Upper Avon and River Avon: a river in central England that flows through Stratford-on-Avon and empties into the Severn

Other synonyms of Upper Avon include Avon, Upper Avon River.

Upper Avon (noun)	River Avon (noun)
a river in central England that flows through Stratford-on-Avon and empties into the Severn	a river in central England that flows through Stratford-on-Avon and empties into the Severn
	a river in southwestern England rising in Gloucestershire and flowing through Bristol to empty into the estuary of the Severn