Embankment (5)
(Other definitions for ridge that I've seen before include "Narrow raised band on a surface" , "Long narrow natural elevation" , "there's a lot of pressure in it" , "Line where two upward sloping surfaces meet" , "back of whale" .)
'embankment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for levee that I've seen before include "Flood embankment" , "Embankment holding water back" , "Riverside embankment" , "An embankment built to prevent a river from overflowing" , "Retaining embankment" .)