Area, quiet river location, is suitable (8)
I believe the answer is:
apposite
'suitable' is the definition.
(thesaurus)
'area quiet river location' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'quiet' becomes 'p' (music symbol for 'piano').
'river' becomes 'po' (Italian river).
'location' becomes 'site' (site is a kind of location).
'a'+'p'+'po'+'site'='APPOSITE'
'is' acts as a link.
(Other definitions for apposite that I've seen before include "Appropriate, pertinent" , "Appropriate, apt" , "Suited for the purpose" , "Appropriate for purpose or occasion" , "Germane" .)