debouch vs flowage

debouch

noun
  • A narrow outlet from which a body of water pours. 

  • A fortress at the end of a defile. 

verb
  • To pour forth from a narrow opening; to emerge from a narrow place like a defile into open country or a wider space. 

flowage

noun
  • A flowing or overflowing of liquid. 

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