River Avon vs Upper Avon

River Avon and Upper Avon both are nouns.

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

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

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

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

River Avon (noun)	Upper 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