A river once more rises and falls (7)
I believe the answer is:
niagara
'falls' is the definition.
(Niagara Falls)
'a river once more rises' is the wordplay.
'river' becomes 'r' (abbreviation).
'once more' becomes 'again' (synonyms).
'rises' says the letters should be written in reverse.
'a'+'r'+'again'='aragain'
'aragain' in reverse letter order is 'NIAGARA'.
'and' acts as a link.
(Other definitions for niagara that I've seen before include "it's quite a height" , "US/Canadian falls" , "Famous 12" , "North American river with famous falls" , "Famous waterfalls" .)