Sudden inundation’s well over western parts of Tewkesbury (5)
I believe the answer is:
spate
'sudden inundation's' is the definition.
(I've seen this in another clue)
'well over western parts of tewkesbury' is the wordplay.
'well' becomes 'spae' (I can't explain this - if you can you should give a lot more credence to this answer).
'over' means one lot of letters goes inside another.
'western parts of' suggests taking the first letters (left most letters).
The first letter of 'tewkesbury' is 't'.
'spae' placed around 't' is 'SPATE'.
Can you help me to learn more?
(Other definitions for spate that I've seen before include "Rush, flood (of river)" , "Fast outpouring" , "A sudden flood or rush" , "A torrent of tapes" , "Flood; sudden burst" .)