Flooding, with one sister (not Ida) affected (10)
I believe the answer is:
Here is my best explanation:
'flooding' is the definition.
'one sister not ida affected' is the wordplay.
'one' becomes 'i' (Roman numeral).
'sister' becomes 'nun' (I've seen this before).
'affected' is an anagram indicator.
'notida' is an anagram of 'dation'.
'with' is the link.
(Other definitions for inundation that I've seen before include "Flood" and "A flood".)