catchment basin vs watershed

catchment basin

noun
  • A topographic region in which all water drains to a common outlet. 

watershed

noun
  • A region of land within which water flows down into a specified body, such as a river, lake, sea, or ocean; a drainage basin. 

  • The topographical boundary dividing two adjacent catchment basins, such as a ridge or a crest. 

  • The time after which material of more adult nature (violence, swear words, sex) may be broadcast on television or radio, either one laid down by law or one contrived from convention (e.g. when children are not watching) 

  • A critical point marking a change in course or development. 

adj
  • Serving to mark a significant development, change in direction, etc. 

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