Periodically escaping to yonder river (4)

I believe the answer is:

tyne

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'river' is the definition.
(river in the North East of England)

I can't explain the rest of the clue.

(Other definitions for tyne that I've seen before include "Serve as evidence for" , "River of NE England" , "Geordie river" , "River of Northumberland" , "River running through Newcastle" .)

I've seen this clue in The Independent.

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