river basin vs water parting

river basin

noun
  • An extent of land where water from rain or snow melt drains downhill into a river or series of rivers. 

water parting

noun
  • A summit from whose opposite sides rainwater flows into different streams; a line separating the drainage districts of two streams or coasts; a divide; a watershed. 

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