drainage vs outfall

drainage

noun
  • A system of drains. 

  • A downward wind. 

  • A natural or artificial means for the removal of fluids from a given area by its draining away. 

outfall

noun
  • The point or place of discharge of a river, drain, culvert, sewer, etc.; mouth; embouchure. 

  • A quarrel; a falling out. 

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