Turning brown - Russian river, as is to be expected (7)
I believe the answer is:
natural
'as is to be expected' is the definition.
(I've seen this before)
'turning brown russian river' is the wordplay.
'turning' shows that the letters should be reversed in order.
'brown' becomes 'tan' (tan is a kind of brown).
'russian river' becomes 'ural' (I've seen this in other clues).
'tan' back-to-front is 'nat'.
'nat'+'ural'='NATURAL'
(Other definitions for natural that I've seen before include "Not made, normal" , "Without affectation" , "Unspoilt" , "Unaffected - musical character" , "Innate - neither flat nor sharp" .)