Points produced by manuscript about old flood defence (5)
I believe the answer is:
marks
'points' is the definition.
(I've seen this before)
'manuscript about old flood defence' is the wordplay.
'manuscript' becomes 'ms' (abbreviation for manuscript).
'about' is an insertion indicator.
'old flood defence' becomes 'ark' (I can't explain this - if you can you should believe this answer much more).
'ms' placed around 'ark' is 'MARKS'.
'produced by' acts as a link.
Can you help me to learn more?
(Other definitions for marks that I've seen before include "Symbols" , "Stains" , "Targets" , "Goals" , "Grades assigned to school work" .)