aqueduct vs floodgate

aqueduct

noun
  • An artificial channel that is constructed to convey water from one location to another. 

  • A structure carrying water over a river or depression, especially in regards to ancient aqueducts. 

  • A structure conveying fluid, such as the cerebral aqueduct or vestibular aqueduct. 

floodgate

noun
  • An adjustable gate or valve used to control the flow of water through a sluice. 

  • Anything that controls or limits an outpouring of people, emotion etc. 

How often have the words aqueduct and floodgate occurred in a corpus of books? (source: Google Ngram Viewer )