Street location lay to impressive river's south (8)
I believe the answer is:
somerset
'street location' is the definition.
(I've seen this before)
'lay to impressive river's south' is the wordplay.
'lay' becomes 'set' (I've seen this in another clue).
'to' means one lot of letters go next to another (I've seen this in other clues).
'impressive river's south' becomes 'somer' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'set' put after 'somer' is 'SOMERSET'.
Can you help me to learn more?
(Other definitions for somerset that I've seen before include "part of the west" , "SW county" , "Cheddar Gorge's county" , "County; acrobat move" , "English territory" .)