Crossword Genius

Turbulent river in Europe, as far as the Guardian is concerned (7)

Ross

I believe the answer is:

riotous

I'm a little stuck... Click here to teach me more about this clue!

'turbulent' is the definition.
(I know that turbulent can be written as riotous)

'river in europe as far as the guardian is concerned' is the wordplay.
I cannot really understand how this works, but
'river' could be 'rio' ('river' in Spanish) and 'rio' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'guardian' could be 'us' (the crossword setter and their Guardian colleagues) and 'us' is found in the answer.
A single letter 'o' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for riotous that I've seen before include "Wild, disorderly" , "Marked by public disorder" , "Involving wild behaviour" , "Rowdy" , "Unrestrained like crowd running amok (7)" .)

I've seen this clue in The Guardian.
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