Rise in this? Flood barriers up to protect nearly everything (3,5)
I believe the answer is:
sea level
'rise in this?' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'flood barriers up to protect nearly everything' is the wordplay.
'flood barriers' becomes 'levees'.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'to protect' is an insertion indicator.
'nearly' means to remove the last letter.
'everything' becomes 'all' (I've seen this before).
'levees' written backwards gives 'seevel'.
'all' with its last letter removed is 'al'.
'seevel' placed around 'al' is 'SEA-LEVEL'.
(Other definitions for sea level that I've seen before include "reference height?" , "Altitude is usually measured as height above . . . . . . . ." , "Standard for measuring map heights" , "Calm conditions" , "From which altitudes are measured" .)