Water may flow along this very narrow street (6)
I believe the answer is:
'water may flow along this' is the definition.
The definition suggests a singular noun which matches the answer.
'very narrow street' is the wordplay.
'very' becomes 'v' (common abbreviation).
'narrow street' becomes 'alley' (I've seen this before).
Can you help me to learn more?
(Other definitions for valley that I've seen before include "Flat area of land flanked by hills" , "one running between hills" , "in victory with large marble" , "Dale, dene or glen" , "one depressed" .)